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Upon completing distillation of one sample, Sample 1 proceed with a new sample tube and receiv- 2 ing flask. Titration Questions 1. Record the normality of the standardized 1. H2SO4 was used to digest the sample, how many millili- 2. How to calibrate the instrument. Put a magnetic would your results have been changed if the alkali pump stir bar in the receiver flask and place it on a timer had malfunctioned and delivered only 15 ml of the stir plate. Molarity of conc. Could phenolphthalein be used as an indicator in the Kjeldahl titration?
Why or why not? Titrate each sample and 3. Describe the function of the following chemicals used in blank to an endpoint pH of 4. Record vol- this determination: ume of HCl titrant used. If using a colorimetric endpoint, put a b Borate magnetic stir bar in the receiver flask, place c H2SO4 it on a stir plate, and keep the solution stir- d NaOH ring briskly while titrating.
Titrate each 4. Why was it not necessary to standardize the boric acid sample and blank with the standardized solution? HCl solution to the first faint gray color. Explain how the factor used to calculate the percent pro- Record volume of HCl titrant used. Data and Calculations 6. For each of the disadvantages of the Kjeldahl method, give Calculate the percent nitrogen and the percent pro- another protein analysis method that overcomes at least tein for each of your duplicate or triplicate corn flour partially that disadvantage.
The corn flour sample you analyzed was not a dried sample. Use 6. Determine the protein content of corn flour using the nitrogen combustion method.
In the assay, the the appropriate slot for the sample number. Sample and to release nitrogen gas and other products i. The other products are removed, and the nitrogen is quantitated by gas chromatography using Data and Calculations a thermal conductivity detector. Record the percent nitrogen content for each of your duplicate or triplicate corn flour samples. Calculate Chemicals protein content from percent nitrogen data, and determine the average percent protein.
The corn flour CAS No. Hazards sample you analyzed was not a dried sample. Report percent protein results on a wet weight basis wwb and Ethylenediaminetetraacetic acid, Irritant on a dry weight basis dwb. The other chemicals used are specific to each manufac- turer for the columns within the instrument. Supplies Questions 1. What are the advantages of the nitrogen combustion Used by students method compared to the Kjeldahl method?
If you analyzed the corn flour sample by both the Kjeldahl Equipment and nitrogen combustion methods, compare the results. Chang SKC Protein analysis. Springer, New York sample cup on an analytical balance. Sample weight AOAC International Official methods of analysis, will be coordinated with sample number in autosam- 18th edn, ; Current through revision 2, On-line. Remove sample from Method Hazards The phenol—sulfuric acid method is a simple and rapid colorimetric method to determine total carbo- D-Glucose C6H12O6 hydrates in a sample.
Although the method detects almost all carbohydrates, the absorptivity of the different carbohydrates varies. These compounds then react with phenol to produce a yellow-gold color. Wear gloves and safety glasses at all times, at nm. For products that are high in hexose sugars, and use good lab technique.
The concentrated H2SO4 is glucose is commonly used to create the standard curve, very corrosive e. The phe- and the absorption is measured at nm. The color nol is toxic and must be discarded as hazardous waste.
In this experiment, you will create a standard curve with a glucose standard solution, use Supplies it to determine the carbohydrate concentration of soft drinks and beer, then calculate the caloric content of Used by students those beverages.
Carbohydrate analysis. Then, pipette 1. Dilute to volume with dd water. Seal flask with Para- Instructions are given for analysis in duplicate. Then, in a test tube, combine the tubes contain 0— ml of glucose use ml 1 ml of the 1: diluted beverage and mechanical pipettor to pipet samples , in a total 1 ml dd water.
Record caloric content from label: You will ana- volumetric flask, and dilute to volume lyze for total carbohydrate content: 1 a regular with dd water. Seal flask with Parafilm and and diet soft drink of the same brand, or 2 a mix well. Before 5. Phenol addition: To each tube from Parts you proceed with the sample preparation and 1 and 4 containing a total volume of 2 ml, analysis, record the caloric content on the nutri- add 0.
Mix on a Vortex test 3. Decarbonate the beverages: With the bever- tube mixer. Shake 5. The sulfuric acid reagent should gently at first try not to foam the sample if it be added rapidly to the test tube. Direct the is beer and continue gentle shaking until no stream of acid against the liquid surface rather observable carbon dioxide bubbles appear.
If than against the side of the test tube in order there is any noticeable suspended material in to obtain good mixing. These reactions are the beverage, filter the sample before analysis. Sample tubes: So the sample tested will contain of H2SO4 to an aqueous sample. After ized. Mix on a Vortex test tube mixer. Let tubes dilution as indicated, pipette 1. Ana- for 10 min i. Vortex the test tubes again before reading the absorbance.
Dilution Volume assayed ml 7. Reading absorbance: Wear gloves to pour Soft drink samples from test tubes into cuvettes. Do not Regular 1 rinse cuvettes with water between samples. Retain this blank sample in one Lite 1 cuvette for later use. Read your standard Sample table: curve tubes from low to high concentration i. Absorbance Spectra: Use one of the duplicate 18 Soft drink, 1: 1 ml 0.
Determine the absorbance spectra from to nm by reading Sample calculation for soft drink, regular: the tube at 10 nm intervals. Construct a standard curve for your total carbo- ond table below.
Calculate the concentration of glucose in your into account the dilution and volume assayed. Note: Glucose equivalent 4. Plot the absorbance spectra obtained by measur- 11 Std. What are the advantages, disadvantages, and sources of diet error for this method to determine total carbohydrates? Your lab technician performed the phenol—H2SO4 analysis on 17 Beer, reg.
What most likely 6. Was it best to have read the absorbance for the standard caused these results? Describe what happened. Explain why a wave- 3. If you started with a glucose standard solution of 10 g length in this region is appropriate for this reaction. Show all calculations. If you had not been told to do a fold dilution of This laboratory was developed with input from Dr a soft drink sample, and if you know the approximate Joseph Montecalvo, Jr.
In: Nielsen content on the food label? Springer, New York ries explain any differences? The U. Food and Drug Administration requires approximately 50 mg ascorbic acid preferably U. The instability of Vitamin C makes it more dif- dard. Record this weight. Transfer to a mL volu- ficult to ensure an accurate listing of Vitamin C content metric flask. Dilute to volume immediately before use on the nutrition label. While this To 50 ml deionized distilled dd water in a method is not official for other types of food products, ml beaker, add and stir to dissolve 42 mg it is sometime used as a rapid, quality control test sodium bicarbonate, then add and stir to dis- for a variety of food products, rather than the more solve 50 mg 2, 6-dichloroindophenol sodium time-consuming microfluorometric method AOAC salt.
Dilute mixture to ml with dd water. Method Close the bottle with a stopper or lid and store refrigerated until used. Official Methods of Analysis, 18th ed. Method 20 ml acetic acid. Add and stir to dissolve 7. Dilute mixture to ml Pegg, R. Vitamin with distilled water. Filter through fluted filter analysis. Close the bottle with a stop- Springer, New York. Filter juices through cheesecloth to avoid problems with pulp when pipetting. Record Principle of Method from the nutrition label for each product the Ascorbic acid reduces the indicator dye to a colorless percent of the Daily Value for Vitamin C.
At the endpoint of titrating an ascorbic acid- containing sample with dye, excess unreduced dye is Hazards, Precautions, and Waste Disposal a rose-pink color in the acid solution. The titer of the Preparation of reagents involves corrosives. Use appro- dye can be determined using a standard ascorbic acid priate eye and skin protection. Otherwise, adhere to solution. Food samples in solution then can be titrated normal laboratory safety procedures. Waste likely may with the dye, and the volume for the titration used to be put down the drain using a water rinse, but follow calculate the ascorbic acid content.
Prepare blanks: Pipette 7. Record the initial and final readings and calcu- Notes late the difference to determine the amount of dye used for each titration. Quantities of supplies and reagents specified are adequate for each student or lab group to standardize Data the dye and analyze one type of orange juice sample in triplicate. Buret start Buret end Vol. Pipette 5 ml metaphosphoric acid—acetic acid Blank 1 solution into each of three ml Erlenmeyer 2 flasks.
Add 2. Using a funnel, fill the buret with the indophe- 3 nol solution dye and record the initial buret reading. Place the Erlenmeyer flask under the tip of the Calculations buret. Slowly add indophenol solution to stan- 1. Swirl the flask as you add the indophenol solution. Repeat steps 3—5 for the other two standard samples. Calculate the mean and stan- 0. Use these 0. How do results available for the juice samples analyzed 1.
Why was it necessary to standardize the indophenol Sample solution? Why was it necessary to titrate blank samples? Why might the Vitamin C content as determined by 1 this method be underestimated in the case of the heat 2 processed juice samples?
In: Nielsen SS ed Food analysis, 4th edn. This blue color is the endpoint of the Background titration. Stoichiometry of the reaction is nesium. This reaction can be used to determine the 1 mol of calcium complexing with 1 mol of EDTA. Endpoints in the titration are detected Chemicals using indicators that change color when they complex with mineral ions.
Calmagite and eriochrome black CAS No. Hazards T EBT are such indicators that change from blue to pink when they complex with calcium and magne- Ammonium chloride Harmful sium. The pH affects a com- for the plexometric EDTA titration in several ways, and must environment be carefully controlled.
Such test strips are available Ethylenediaminetetraacetic Irritant from various companies. E and Carpenter, C. Traditional methods Magnesium sulfate, for mineral analysis. In 50 ml deionized distilled dd Principle of Method water, dissolve 1. Combine complex with calcium or magnesium at pH Store in a tightly black T EBT , are pink when complexed to metal stoppered Pyrex or plastic bottle to prevent ions but blue when no metal ions are complexed to loss of ammonia NH3 or pickup of carbon them.
The indicators bind to metal ions less strongly dioxide CO2. Dispense this buffer solution than does EDTA. When the indicator is added to a with a repipette system. Discard buffer when solution containing metal ions, the solution becomes 1—2 ml added to a sample fails to give pH pink. When EDTA is added as titrant to the mineral- Transfer to a ml Erlen- meyer flask. HCl:H2O , a little Adhere to normal laboratory safety procedures.
Wear at a time, until all the CaCO3 has dissolved gloves and safety glasses at all times. The buffer make sure all the CaCO3 in the neck of the flask solution, which contains ammonium hydroxide, has been washed down with HCl. Add ml should be disposed of as hazardous waste. Adjust to pH 3. HCl:H2O , as required. Transfer by environmental health and safety protocols at your quantitatively to a 1-L volumetric flask, and institution. Dilute to 1 L Used by students with dd water.
Mix carefully. Use 1 ml per 30 ml solution to be titrated. With increasing pH, the sharpness of the endpoint increases. However, at high pH, the indi- Procedure cator dye changes color and there is risk of precipi- Modified from Method Hardness, Standard Meth- tating calcium carbonate CaCO3 or magnesium ods for the Examination of Water and Wastewater, 21st ed.
The tendency toward CaCO3 precipita- Instructions are given for analysis in triplicate. Certain inhibitors 1. Pipette 10 ml of calcium standard solution can be added before titration to reduce this interfer- into each of three ml Erlenmeyer flasks. Adjust to pH Magnesium salt of 1,2-cyclo- If possible, do this pH adjustment with the hexanediaminetetraacetic acid MgCDTA , which buffer in an operating hood, due to its odor.
However, for samples with pH adjustment. Color may first appear lavender or purple, 1 2 but will then turn to blue. Complete titration 3 within 5 min from time of buffer addition. Prepare samples in triplicate. Record the volume of EDTA solution used 1. If a sample of water is thought to have a hard- for each titration.
Data and Calculations 2. Other similar test strips could be used. The strips are dipped into the water to test Note: Test the same tap water, tap distilled water, and for total hardness caused by calcium and magnesium. The calcium displaces the magnesium bound to EDTA, and the released magnesium binds to Calmagite, caus- 1. Dip the test strip into a beaker filled with ing the test strip to change color. Follow instructions on strip about how to read it, relat- Chemicals ing color to ppm CaCO3.
Compare and discuss the accuracy and precision and concentrated HCl. No precautions are needed in use of the test strip. Adhere to normal laboratory safety procedures. American Public IN. Several chromogens daily. Wear tify the mineral in beef samples. Waste may be put down the In this experiment, meat samples are first ashed to drain using water rinse. The acid is necessary Supplies to keep the mineral in solution. Ferrozine complexes only with ferrous iron and not with ferric iron.
Traditional methods for mineral analysis. Instructions are given for analysis in duplicate. Objective Determine the iron content of food samples using the Ashing ferrozine method. Principle of Method 2. Heat on the hot plate until the sample is well- Ferrous iron in extracts or ashed samples reacts with fer- charred and has stopped smoking.
Iron is is white. Iron Measurement 1. Make dilutions using ca 0. Hazard s 2. Dissolve ash in small amount of 1 N HCl, and dilute to 50 ml in volumetric flask with 3- 2-pyridyl -5,6-bis 0. In duplicate, put 0. Sigma P 4. Add 1. Vortex and let set 10 min.
Ammonium acetate 5. Vortex Calculation of total iron in sample: and let set in dark for 15 min. Plot the standard curve and determine the 7. Take two readings repeated measures, msmt mg iron for each tube at nm. How else could iron be determined using the wet ash digest?
What would be the advantages and disadvantages 0 blank of the ferrozine method versus the other method you 2 identified? These methods are official methods of analysis commercially available from companies that sell the for numerous specific products. All these methods electrodes : electrode rinse solution, ionic strength are faster and less expensive procedures than analy- adjustor, reference electrode fill solution, standard sis by atomic absorption spectroscopy or inductively solution, electrode storage solution.
Strength Adjustor to 1 L with deionized distilled dd water. For chloride electrode — Deionized Reading Assignment distilled water. Ward, R. For chloride electrode: 5 M NaNO3. HNO3 to 1 L with dd water. Sensing and reference Hazards, Precautions, and Waste Disposal electrodes are immersed in a solution that contains the Adhere to normal laboratory safety procedures. Wear element of interest. The electrical potential that develops gloves and safety glasses at all times.
Ammonium at the surface of the sensing electrode is measured by hydroxide waste should be discarded as hazardous comparing the reference electrode with a fixed potential. Other waste likely can be put down the drain The voltage between the sensing and reference electrodes using a water rinse, but follow the laboratory practices relates to the activity of the reactive species.
Remove from hot plate and cool to room temperature in the hood. Filter water extract Cat. NA II. Sample Analysis by ISE 1. Condition sodium electrode as specified by the Procedure manufacturer. Replicate the preparation and analysis of standards 2. Assemble, prepare, and check sodium and and samples as specified by the instructor. Sample Preparation General Instructions 3.
Connect electrodes to meter according to meter instruction manual. Prepare samples by adding 5 g or 5 ml of 4. For instruments with direct concentration sample prehomogenized if necessary, and readout capability, consult meter manual for diluted if necessary to a ml volumetric correct direct measurement procedures. Add 2 ml ISA, then dilute to volume 5.
Using the pH meter set on mV scale, determine with dd water. See instructions specific for the potential mV of each standard solution each type of food product below. Samples 1, 10, , , ppm , starting with the with high fat levels may require fat removal. Use a uniform stirring Consult technical services of the company that rate, with a magnetic stir bar in each solution, manufactures the ISE. Prepare standards by adding 5 ml standard of 6. Rinse electrodes with electrode rinse solution proper dilution e.
Measure samples and record the mV reading. Add 2 ml ISA, then dilute to volume with As you rinse electrodes with electrode rinse dd water. Therefore since samples that the hole is covered. After use, store sodium electrode and reference rection for this dilution needs to be made in electrode as specified by manufacturer. Data and Calculations Specific Samples: 1. Prepare a standard curve using 5-cycle semilog Sports drink: No dilution is required before paper, with concentration plotted on the log a 5-ml sample is combined with the 2-ml ISA axis.
Plot actual concentration values on the and dd water as described above. Concentrations may Catsup: Accurately weigh ca. Also, be sure to rinse all pipettes, burets, beakers, flasks, etc. Objective to remove residual AgNO3 when you are finished Determine the sodium content of various foods with this experiment.
Otherwise, these items also using the Mohr titration method to measure chloride will stain, and drip stains are likely to appear on the content. Potassium chromate and silver nitrate must be disposed of as a hazardous waste. Other waste likely can be put down the drain using a water rinse, Principle of Method but follow good laboratory practices outlined by The Mohr titration is a direct titration method to environmental health and safety protocols at your quantitate chloride ions, to then calculate sodium ions.
The chloride-containing sample solution is titrated with a standard solution of silver nitrate. Procedure 4. Filter each solution through glass wool. Transfer Instructions are given for analysis in triplicate. Add 1 ml of potassium chromate indicator to I. Standardization of ca. Titrate each solution with standardized ca.
Transfer ml of the 0. This solution will be standard- color that persists for 30 s. Record the volume of ized, then used to titrate the food samples. Fill a titrant used. Accurately weigh to four decimal places about mg KCl into 1. Weigh accurately approximately 5 g of potato three ml Erlenmeyer flasks. Dissolve in chips in duplicate into ml beakers, then add dd water about 25 ml , add 2—3 drops of 95 ml boiling dd water to each beaker.
Stir the mixture vigorously for 30 s, wait for mate may cause serious skin sensitivity reac- 1 min, stir again for 30 s, then let cool to room tions!
Put a magnetic stir bar in each flask with 3. Transfer the KCl solution, and place the beaker on a 50 ml of each solution to ml Erlenmeyer magnetic stir plate below the buret for titration.
Using the AgNO3 solution in the buret, titrate 4. Add 1 ml of potassium chromate indicator to the KCl solutions to the appearance of the first each 50 ml of filtrate.
Note: you 5. This color that persists for 30 s. Record the volume of endpoint is due to the formation of Ag2CrO4. Pipette accurately 5 ml of sports drink in 4. Record volume of AgNO3. Calculate and record molarity of AgNO3. Stir the mixture vigorously for 30 s, wait for gKC1 1molKC1 ml 1 min, stir again for 30 s.
Add 1 ml of potassium chromate indicator to 6. Label bottle of AgNO3 with your name and the each 50 ml of prepared sample. Record the volume of II. Sample Analysis by Mohr Titration titrant used. Cottage Cheese Data and Calculations 1. Accurately weigh 10 g of cottage cheese in triplicate into ml beakers.
Calculate the chloride content and the sodium 2. Mix to a thin paste using a glass then calculate the mean and standard deviation stirring rod or spatula. Add another ca. Note that answers must titration, b Volhard titration? The reaction of silver dichromate with ml chloride ions produces a white column of silver chloride in the strip.
When the strip is completely saturated with the liquid, a moisture-sensitive signal across the top of Buret Buret Vol. The value on the numbered scale is read 3 at the tip of the color change, and then is converted to percent salt using a calibration table.
Would this Mohr titration procedure as described above work well to determine the salt content of grape juice or Dilute 5 ml of the stock solution to ml with catsup?
How did this method differ from what would be done sodium chloride solution to use as a standard using a Volhard titration procedure? Repeat Steps 1—5 given above using the 0. Stir mixture vigorously for 30 s, wait for 1 min, stir as NaCl. Company, Elkhart, IN, Contact 3. Instructions are given for analysis in triplicate.
Transfer 50 ml of the 0. Note that each lot of chloride solution to a ml beaker. Fold a piece of filter paper into a cone-shaped sure to use the correct calibration chart i. Multiply the result by the dilution factor 20 3. Using the 0. Weigh accurately approximately 5 g of potato than 2. Crush chips with a 4. Thirty seconds after the moisture-sensitive sig- glass stirring rod. Add 95 ml boiling dd water nal string at the top of the titrator turns dark and stir. Filter water extract into a ml volumetric reading at the tip of the yellow-white peak, to flask, using a funnel with glass wool.
Let cool the nearest 0. Using the calibration chart included with the Transfer to a ml beaker. Follow Steps 3—7 from the procedure for cottage ing to percent sodium chloride NaCl and cheese. Be Catsup sure to use the correct calibration chart i. Weigh accurately approximately 5 g of catsup control number on the product being used must into a ml beaker. Add 95 ml boiling dd match the control number on the bottle.
Transfer to a ml beaker. Product electrode titration titrator label Data 3. Follow Steps 3—7 from the procedure for cot- — tage cheese. Follow Steps II. Questions Data and Calculations 1. Based on the results and characteristics of the methods, discuss the relative advantages and disadvantages of each From calibration chart Corrected for dilution factor method of analysis for these applications.
Include in the table the sodium cheese, indicating strip method. Part The aim of coupled plasma-atomic emission spectroscopy. In this experiment, the term AES will be amount of energy emitting from the hollow cathode used rather than OES, but the two terms are inter- lamp and that reaching the detector.
Absorption is lin- changeable. This experiment specifies the preparation of stan- Atomic emission is based on atoms emitting energy, dards and samples for determining the sodium Na after heat energy from a flame has converted molecules and potassium K contents by AAS and ICP-AES.
The to atoms, and then raised the atoms from ground state samples suggested for analysis include two solid food to an excited state. One measures the amount of emit- product that does not a clear sports drink, or a clear ted energy of a wavelength specific for the element of fruit juice.
Emission is linearly related to concentration. Procedures for both wet ashing and dry ashing Chemicals of the solid samples are described. Experience can be gained with both types of ashing, and the results of the two methods can be compared. Sodium results from this CAS No. Lanthanum chloride LaCl3 Irritant The limit of detection for sodium is 0. The limit of detection std. Ash analysis. Miller, D. Atomic absorption spec- Used to prepare ml solutions of each of troscopy, atomic emission spectroscopy, and inductively the concentrations listed in Table Each coupled plasma mass spectrometry.
Wear used, likely with the same standard solutions and samples safety glasses and gloves during sample preparation. Use acids in a hood. Shake well. Wet Ashing Supplies Note: Digestion procedure described is a wet digestion Used by students with nitric acid and hydrogen peroxide. Other types of digestion can be used instead.
Accurately weigh out — mg of each digestion block sample and place in a digestion tube. Let the samples cool for at least 30 min. As soon as the reaction Sample Preparation: Liquid Samples starts, remove the tubes from the block, and 1. Put an appropriate volume of liquid sample in let the reaction continue in the cooling rack. For a sports drink, Caution: Some sample types will have a use 0.
Add 10 ml conc. Repeat Steps 8 and 9 for all the samples and the 3. Add deionized distilled dd water to volume. Put all the tubes in the digestion block, and 6. Make appropriate dilution of samples with leave until ca. Table If the tubes are left on the digestion 7. If necessary, filter samples using Whatman block too long and they become dry, remove, hardened ashless filter paper into container cool, and carefully add ca.
Turn off the digestion block when all the tubes have been Analysis digested and removed. Take appro- Table AAS, and the liquid or gas argon and the plasma in Analyze standards, reagent blanks, hardened ashless filter paper into container and samples. Accurately weigh out blended or ground ca. Pre-dry sample over boiling water bath. Hg, for 16 h.
Dissolve ash in 10 ml HCl solution , appropriate standard curve. Note: For the AAS samples, you need to subtract Standard Curve Data the liquid blank absorbance from the sports drink sample values, and the solid blank absorbance Potassium Standard Curves Sodium Standard Curves from the catsup and potato chip sample values.
If emission data are not Sample Data available for the samples, record the concentra- tions in ppm of sodium and potassium for the Atomic Absorption Spectroscopy food samples as analyzed i. Show examples 2 of all calculations below the table.
Cottage 1 chesse 2 Potato 1 chips 2 Questions 1. Compare the sodium and potassium values for catsup Inductively Coupled Plasma — Atomic Emission and potato chips to those reported in the U. Describe how you would prepare the Na and K standard Liquid 1 — — — solutions for AES, using the ppm solutions of each, blank 2 — — — which are commercially available. If possible, all solutions Sports 1 for points in the standard curve should be made using drink 2 different volumes of the same stock solution.
Do not use Solid 1 — — — volumes of less than 0. Make all standards to the same blank 2 — — — volume of ml. Note that each standard solution must Catsup 1 contain 10 ml conc. Cottage 1 3. Describe how you would prepare a ppm Na solu- chesse 2 tion, starting with commercially available solid NaCl. Springer, New York 1. Use the standard curves from AAS and the plasma mass spectrometry. In: Nielsen SS ed absorption readings of the samples to deter- Food analysis, 4th edn.
Such a solution is referred to as a standard solution. The assay for titratable acidity is a volumetric method that uses a standard solution and, most commonly, the Principle of Method indicator phenolphthalein. In the titration, a standard solution of sodium hydroxide reacts with the organic A standard acid can be used to determine the exact acids present in the sample. The normality of the sodium normality of a standard base, and vice versa.
A standard acid such as potassium acid phthalate can be used to determine the exact normality CAS No. Hazards of the standard sodium hydroxide used in the titration. When colored Phenolphthalein Irritant solutions obscure the pink endpoint, a potentiomet- Potassium acid phthalate Irritant ric method is commonly used. Springer, New York. Allow the water to cool with ascarite protection.
Therefore, CO2-free water is prepared and used for standardizing acids and base and for determining Dissolve 1. Put in bottle with titratable acidity. An ascarite trap is attached to bottles of eyedropper.
While Use appropriate precautions in handling concentrated adding about 40 ml of dd water, stir the NaOH acid and base. Otherwise, adhere to normal laboratory pellets with a glass stirring rod. Continue safety procedures. Wear gloves and safety glasses at all stirring until all pellets are dissolved.
Quan- times. Waste may be put down the drain using a water titatively transfer the NaOH solution into rinse, but follow good laboratory practices outlined by a ml volumetric flask.
Dilute to volume environmental health and safety protocols at your insti- with dd water. The solution must be cooled tution.
Store this solution in a plastic bottle and label Supplies appropriately. Prepare ca. Add ca. Standardize ca. Record the exact weights. Add Equipment ca. Record the beginning and Calculations Required before Lab ending volume on the buret. Titration should proceed to the faintest tinge of pink that persists 1. Calculate how much NaOH to use to prepare for 15 s. Record the total volume of NaOH used Preface for definition of percent solutions.
Data from this part will 2. Calculate how much concentrated HCl to use be used to calculate the mean normality of the to prepare ml of ca. Remember that you have your stan- 1. To duplicate. Record the volumes used. Describe in detail how you standardized your ca. The range Determine the titratable acidity and pH of food samples. Prepared as described in Method A.
HCl ml Vol. Wear safety glasses at all times. Waste likely may be put down the drain using a water rinse, but follow good Questions laboratory practices outlined by environmental health 1. How would you and safety protocols at your institution. Describe how you prepared the ml of ca. Supplies Show your calculations. Also, observe any color changes that occur Equipment during the titration to determine when the phenol- phthalein endpoint is reached. Sample B without phenolphthalein does not need to be followed with the pH meter, but is to be Procedure titrated along with the other beaker to aid in observing I.
Soda color changes. Do at least duplicate determinations for unboiled soda Data and Calculations and for boiled soda sample; open soda well before use to allow escape of carbon dioxide so that the sample can I. Soda be pipetted. Using the volume of NaOH used, calculate the titrat- 1. Unboiled soda: Pipette 20 ml of soda into a able acidity TA of each soda sample as percent- ml Erlenmeyer flask.
Record the beginning and ending vol- umes on the buret to determine the total volume Buret Buret Vol. Observe Rep start end titrant fades? TA the endpoint. Note whether the color fades. Boiled soda: Pipette 20 ml of soda into a ml Unboiled soda: Erlenmeyer flask. Bring the sample to boiling 1 on a hot plate, swirling the flask often. Boil the 2 sample only 30—60 s.
Cool to room temperature. Add 3 drops of the phenolphthalein solution and titrate as Boiled soda: described above. Observe the endpoint. Sample calculation: II. Standardize the pH meter with pH 7. Apple Juice to each. What caused the color changes in the apple juice titrated ml NaOH 1 2 3 4 5 6 7 8 9 10 without any phenolphthalein present? Hint: Consider the pigments in apples. How would you recommend deter- pH mining the endpoint in the titration of tomato juice?
You are determining the titratable acidity of a large num- ber of samples. You ran out of freshly boiled dd H2O with an ascarite trap on the water container, so you switch ml NaOH 11 12 13 14 15 16 17 18 19 20 to using tap distilled H2O.
Would this likely affect your results? The electrode of your pH meter has a slow response time and seems to need cleaning, since it is heavily used for a variety of solutions high in proteins, lipids, and minerals. Plot pH versus ml of 0.
As the new lab supervisor, you have the sample that contained phenolphthalein Beaker C. What solutions would you use to try to clean phenolphthalein endpoint.
Springer, 1. Soda samples. Lipids in food are subjected to many chemical reactions The solution should be clear. The Prepare ca. Determine the exact nor- laboratory deals with the characterization of fats and oils mality using a solution of standard base. Use hydrochloric acid in a fume hood.
Otherwise, adhere to normal laboratory safety procedures. Wear Overall Objective safety glasses at all times. Wastes likely may be put down the drain using a water rinse, but follow good The overall objective of this laboratory is to determine laboratory practices outlined by environmental health aspects of the composition, structure, and reactivity of and safety protocols at your institution.
Hazards Instructions are given for analysis in duplicate. Ethanol Highly flammable 1. Melt any solid samples. Filter melted fat sample Hydrochloric acid Corrosive and oil sample through filter paper to remove HCl impurities. Phenolphthalein Irritant 2.
Weigh accurately ca. Record weight of sample. Prepare sample in duplicate. Add accurately from a buret 50 ml of alcoholic Reagents KOH into the flask. Prepare duplicate blank samples with just 50 ml by the laboratory assistant before class. Add several boiling beads to the flasks with fat Questions or oil sample. What is meant by unsaponifiable matter in lipid samples? Connect the flasks with the samples to a con- Give an example of such a type of compound.
Boil gently but steadily on a hot plate 2. What does a high versus a low saponification value tell or water bath until the sample is clear and you about the name of a sample? Objective 7. Allow the samples to cool somewhat. Wash Determine the iodine value of fats and oils. Disconnect flask Principle of Method from condenser.
Allow the samples to cool to room temperature. The iodine value or number is a measure of the 8. Add 1 ml phenolphthalein to samples and degree of unsaturation, defined as the grams of iodine titrate with 0.
In the assay, a measured pink color just disappears. Record the volume quantity of fat or oil dissolved in solvent is reacted of titrant used. Repeat Steps 5—8 with sample blanks. Reflux other halogen, which reacts with the carbon—carbon the blanks for the same time period as used for double bonds.
After a solution of potassium iodide the sample. The calcu- lated amount of iodine reacted with the double bonds is used to calculate the iodine value.
Boil gently for 5 min. Dissolve 2 g potas- sium iodide KI in 80 ml chlorine-free water. Add Equipment this water to the potassium dichromate. To this solution, add, with swirling, 20 ml ca. Melt any samples that are solid at room Mix ca. Add ml boiling above the melting point. Filter melted fat dd water.
She has received teaching awards from her department, college, university, and the Institute of Food Technologists. She has edited five editions of a textbook and three editions of a laboratory manual for Food Analysis.
Skip to main content Skip to table of contents. Advertisement Hide. This service is more advanced with JavaScript available. Food Analysis Laboratory Manual. Authors view affiliations S. Suzanne Nielsen. Front Matter Pages i-xi. Front Matter Pages Gordon Grant, Peter Sporns, Y. Peggy Hsieh. Examination of Foods for Extraneous Materials. High Performance Liquid Chromatography. Gas Chromatography. Page 1 Navigate to page number of 2. Absorption Calcium Vitamin Vitamin C color enzymes extraction spectroscopy viscosity.
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Complexometric Determination of Calcium. Standard Solutions and Titratable Acidity. Fat Characterization. Enzyme Analysis to Determine Glucose Content. Gliadin Detection in Food by Immunoassay. Gordon Grant, Peter Sporns, Y. Peggy Hsieh. Examination of Foods for Extraneous Materials. High Performance Liquid Chromatography. Gas Chromatography. Page 1 Navigate to page number of 2. Add 2. Using a funnel, fill the buret with the indophe- 3 nol solution dye and record the initial buret reading.
Place the Erlenmeyer flask under the tip of the Calculations buret. Slowly add indophenol solution to stan- 1. Swirl the flask as you add the indophenol solution.
Repeat steps 3—5 for the other two standard samples. How do results available for the juice samples analyzed 1. Why was it necessary to standardize the indophenol Sample solution? Why was it necessary to titrate blank samples? Why might the Vitamin C content as determined by 1 this method be underestimated in the case of the heat 2 processed juice samples? In: Nielsen SS ed Food analysis, 4th edn. This blue color is the endpoint of the Background titration.
Stoichiometry of the reaction is nesium. This reaction can be used to determine the 1 mol of calcium complexing with 1 mol of EDTA. Endpoints in the titration are detected Chemicals using indicators that change color when they complex with mineral ions.
Calmagite and eriochrome black CAS No. Hazards T EBT are such indicators that change from blue to pink when they complex with calcium and magne- Ammonium chloride Harmful sium. The pH affects a com- for the plexometric EDTA titration in several ways, and must environment be carefully controlled. Such test strips are available Ethylenediaminetetraacetic Irritant from various companies. E and Carpenter, C. Traditional methods Magnesium sulfate, for mineral analysis.
In 50 ml deionized distilled dd Principle of Method water, dissolve 1. Combine complex with calcium or magnesium at pH Store in a tightly black T EBT , are pink when complexed to metal stoppered Pyrex or plastic bottle to prevent ions but blue when no metal ions are complexed to loss of ammonia NH3 or pickup of carbon them.
The indicators bind to metal ions less strongly dioxide CO2. Dispense this buffer solution than does EDTA. When the indicator is added to a with a repipette system. Discard buffer when solution containing metal ions, the solution becomes 1—2 ml added to a sample fails to give pH pink.
When EDTA is added as titrant to the mineral- Transfer to a ml Erlen- meyer flask. HCl:H2O , a little Adhere to normal laboratory safety procedures. Wear at a time, until all the CaCO3 has dissolved gloves and safety glasses at all times. The buffer make sure all the CaCO3 in the neck of the flask solution, which contains ammonium hydroxide, has been washed down with HCl.
Add ml should be disposed of as hazardous waste. Adjust to pH 3. HCl:H2O , as required. Transfer by environmental health and safety protocols at your quantitatively to a 1-L volumetric flask, and institution. Dilute to 1 L Used by students with dd water. Mix carefully. Use 1 ml per 30 ml solution to be titrated. With increasing pH, the sharpness of the endpoint increases. However, at high pH, the indi- Procedure cator dye changes color and there is risk of precipi- Modified from Method Hardness, Standard Meth- tating calcium carbonate CaCO3 or magnesium ods for the Examination of Water and Wastewater, 21st ed.
The tendency toward CaCO3 precipita- Instructions are given for analysis in triplicate. Certain inhibitors 1. Adjust to pH Magnesium salt of 1,2-cyclo- If possible, do this pH adjustment with the hexanediaminetetraacetic acid MgCDTA , which buffer in an operating hood, due to its odor.
However, for samples with pH adjustment. Color may first appear lavender or purple, 1 2 but will then turn to blue. Complete titration 3 within 5 min from time of buffer addition. Prepare samples in triplicate. Record the volume of EDTA solution used 1. If a sample of water is thought to have a hard- for each titration. Data and Calculations 2. Other similar test strips could be used.
The strips are dipped into the water to test Note: Test the same tap water, tap distilled water, and for total hardness caused by calcium and magnesium.
The calcium displaces the magnesium bound to EDTA, and the released magnesium binds to Calmagite, caus- 1. Dip the test strip into a beaker filled with ing the test strip to change color. Follow instructions on strip about how to read it, relat- Chemicals ing color to ppm CaCO3. Compare and discuss the accuracy and precision and concentrated HCl.
No precautions are needed in use of the test strip. Adhere to normal laboratory safety procedures. Wastes likely may be put down the drain using a water rinse, but follow Resource Materials good laboratory practices outlined by environmental health and safety protocols at your institution.
American Public IN. Several chromogens daily. Wear tify the mineral in beef samples. Waste may be put down the In this experiment, meat samples are first ashed to drain using water rinse.
The acid is necessary Supplies to keep the mineral in solution. Ferrozine complexes only with ferrous iron and not with ferric iron. Traditional methods for mineral analysis. Instructions are given for analysis in duplicate. Objective Determine the iron content of food samples using the Ashing ferrozine method.
Principle of Method 2. Heat on the hot plate until the sample is well- Ferrous iron in extracts or ashed samples reacts with fer- charred and has stopped smoking. Iron is is white. Iron Measurement 1. Make dilutions using ca 0. Hazard s 2. In duplicate, put 0. Sigma P 4. Add 1. Vortex and let set 10 min.
Ammonium acetate 5. Vortex Calculation of total iron in sample: and let set in dark for 15 min. Plot the standard curve and determine the 7. Take two readings repeated measures, msmt mg iron for each tube at nm. How else could iron be determined using the wet ash digest? What would be the advantages and disadvantages 0 blank of the ferrozine method versus the other method you 2 identified?
These methods are official methods of analysis commercially available from companies that sell the for numerous specific products. All these methods electrodes : electrode rinse solution, ionic strength are faster and less expensive procedures than analy- adjustor, reference electrode fill solution, standard sis by atomic absorption spectroscopy or inductively solution, electrode storage solution.
Strength Adjustor to 1 L with deionized distilled dd water. For chloride electrode — Deionized Reading Assignment distilled water. For chloride electrode: 5 M NaNO3. HNO3 to 1 L with dd water. Sensing and reference Hazards, Precautions, and Waste Disposal electrodes are immersed in a solution that contains the Adhere to normal laboratory safety procedures. Wear element of interest. The electrical potential that develops gloves and safety glasses at all times.
Ammonium at the surface of the sensing electrode is measured by hydroxide waste should be discarded as hazardous comparing the reference electrode with a fixed potential.
Other waste likely can be put down the drain The voltage between the sensing and reference electrodes using a water rinse, but follow the laboratory practices relates to the activity of the reactive species. Remove from hot plate and cool to room temperature in the hood. Filter water extract Cat.
NA II. Sample Analysis by ISE 1. Condition sodium electrode as specified by the Procedure manufacturer. Replicate the preparation and analysis of standards 2. Assemble, prepare, and check sodium and and samples as specified by the instructor.
Sample Preparation General Instructions 3. Connect electrodes to meter according to meter instruction manual. Prepare samples by adding 5 g or 5 ml of 4. For instruments with direct concentration sample prehomogenized if necessary, and readout capability, consult meter manual for diluted if necessary to a ml volumetric correct direct measurement procedures. Add 2 ml ISA, then dilute to volume 5. Using the pH meter set on mV scale, determine with dd water.
See instructions specific for the potential mV of each standard solution each type of food product below. Samples 1, 10, , , ppm , starting with the with high fat levels may require fat removal.
Use a uniform stirring Consult technical services of the company that rate, with a magnetic stir bar in each solution, manufactures the ISE. Prepare standards by adding 5 ml standard of 6. Rinse electrodes with electrode rinse solution proper dilution e. Measure samples and record the mV reading.
Add 2 ml ISA, then dilute to volume with As you rinse electrodes with electrode rinse dd water. Therefore since samples that the hole is covered. After use, store sodium electrode and reference rection for this dilution needs to be made in electrode as specified by manufacturer.
Data and Calculations Specific Samples: 1. Prepare a standard curve using 5-cycle semilog Sports drink: No dilution is required before paper, with concentration plotted on the log a 5-ml sample is combined with the 2-ml ISA axis. Plot actual concentration values on the and dd water as described above. Concentrations may Catsup: Accurately weigh ca. Combine 5 ml of tion of the line. Note: If the standard curve this diluted sample with 2-ml ISA and dd is really a curve and not a straight line, read water as described above.
Use the standard curve and the mV readings containing a stir bar. Add ml 0. Show all Prepare approximately ml of the ca. Calculate sodium chloride content of each food, each student or lab group. Students should based on the chloride content.
Calculate the sodium content of each food, in the Procedure. Compare the sodium chloride contents of the Hazards, Precautions, and Waste Disposal foods you analyzed to those reported in the Wear gloves and safety glasses at all times, and use U. Use of crystalline www. AgNO3 or solutions of the silver salt can result in dark brown stains caused by photodecomposition of Question the salt to metallic silver.
These stains are the result 1. If you used both a sodium and chloride ISE, which elec- of poor technique on the part of the analyst, with trode worked better, concerning accuracy, precision, and spilled AgNO3 causing discoloration of the floor. If time to response? Explain your answer, with appropriate you do spill this solution, immediately sponge up justification. Also, be sure to rinse all pipettes, burets, beakers, flasks, etc.
Objective to remove residual AgNO3 when you are finished Determine the sodium content of various foods with this experiment. Otherwise, these items also using the Mohr titration method to measure chloride will stain, and drip stains are likely to appear on the content.
Potassium chromate and silver nitrate must be disposed of as a hazardous waste. Other waste likely can be put down the drain using a water rinse, Principle of Method but follow good laboratory practices outlined by The Mohr titration is a direct titration method to environmental health and safety protocols at your quantitate chloride ions, to then calculate sodium ions.
The chloride-containing sample solution is titrated with a standard solution of silver nitrate. Procedure 4. Filter each solution through glass wool. Transfer Instructions are given for analysis in triplicate. Add 1 ml of potassium chromate indicator to I. Standardization of ca. Titrate each solution with standardized ca. Transfer ml of the 0. This solution will be standard- color that persists for 30 s. Record the volume of ized, then used to titrate the food samples.
Fill a titrant used. Accurately weigh to four decimal places about mg KCl into 1. Weigh accurately approximately 5 g of potato three ml Erlenmeyer flasks. Dissolve in chips in duplicate into ml beakers, then add dd water about 25 ml , add 2—3 drops of 95 ml boiling dd water to each beaker. Stir the mixture vigorously for 30 s, wait for mate may cause serious skin sensitivity reac- 1 min, stir again for 30 s, then let cool to room tions! Put a magnetic stir bar in each flask with 3.
Transfer the KCl solution, and place the beaker on a 50 ml of each solution to ml Erlenmeyer magnetic stir plate below the buret for titration. Using the AgNO3 solution in the buret, titrate 4. Add 1 ml of potassium chromate indicator to the KCl solutions to the appearance of the first each 50 ml of filtrate.
Note: you 5. This color that persists for 30 s. Record the volume of endpoint is due to the formation of Ag2CrO4. Pipette accurately 5 ml of sports drink in 4.
Record volume of AgNO3. Calculate and record molarity of AgNO3. Stir the mixture vigorously for 30 s, wait for gKC1 1molKC1 ml 1 min, stir again for 30 s. Add 1 ml of potassium chromate indicator to 6. Label bottle of AgNO3 with your name and the each 50 ml of prepared sample.
Record the volume of II. Sample Analysis by Mohr Titration titrant used. Cottage Cheese Data and Calculations 1. Accurately weigh 10 g of cottage cheese in triplicate into ml beakers. Calculate the chloride content and the sodium 2. Mix to a thin paste using a glass then calculate the mean and standard deviation stirring rod or spatula. Add another ca. Note that answers must titration, b Volhard titration? The reaction of silver dichromate with ml chloride ions produces a white column of silver chloride in the strip.
When the strip is completely saturated with the liquid, a moisture-sensitive signal across the top of Buret Buret Vol. The value on the numbered scale is read 3 at the tip of the color change, and then is converted to percent salt using a calibration table.
Would this Mohr titration procedure as described above work well to determine the salt content of grape juice or Dilute 5 ml of the stock solution to ml with catsup? How did this method differ from what would be done sodium chloride solution to use as a standard using a Volhard titration procedure? Repeat Steps 1—5 given above using the 0. Stir mixture vigorously for 30 s, wait for 1 min, stir as NaCl. Company, Elkhart, IN, Contact 3. Instructions are given for analysis in triplicate.
Transfer 50 ml of the 0. Note that each lot of chloride solution to a ml beaker. Fold a piece of filter paper into a cone-shaped sure to use the correct calibration chart i. Multiply the result by the dilution factor 20 3. Using the 0. Weigh accurately approximately 5 g of potato than 2. Crush chips with a 4. Thirty seconds after the moisture-sensitive sig- glass stirring rod.
Add 95 ml boiling dd water nal string at the top of the titrator turns dark and stir. Filter water extract into a ml volumetric reading at the tip of the yellow-white peak, to flask, using a funnel with glass wool. Let cool the nearest 0. Using the calibration chart included with the Transfer to a ml beaker.
Follow Steps 3—7 from the procedure for cottage ing to percent sodium chloride NaCl and cheese. Be Catsup sure to use the correct calibration chart i. Weigh accurately approximately 5 g of catsup control number on the product being used must into a ml beaker.
Add 95 ml boiling dd match the control number on the bottle. Transfer to a ml beaker. Product electrode titration titrator label Data 3. Follow Steps 3—7 from the procedure for cot- — tage cheese. Follow Steps II. Questions Data and Calculations 1. Based on the results and characteristics of the methods, discuss the relative advantages and disadvantages of each From calibration chart Corrected for dilution factor method of analysis for these applications. Include in the table the sodium cheese, indicating strip method.
Part The aim of coupled plasma-atomic emission spectroscopy. In this experiment, the term AES will be amount of energy emitting from the hollow cathode used rather than OES, but the two terms are inter- lamp and that reaching the detector.
Absorption is lin- changeable. This experiment specifies the preparation of stan- Atomic emission is based on atoms emitting energy, dards and samples for determining the sodium Na after heat energy from a flame has converted molecules and potassium K contents by AAS and ICP-AES.
The to atoms, and then raised the atoms from ground state samples suggested for analysis include two solid food to an excited state. One measures the amount of emit- product that does not a clear sports drink, or a clear ted energy of a wavelength specific for the element of fruit juice.
Emission is linearly related to concentration. Procedures for both wet ashing and dry ashing Chemicals of the solid samples are described.
Experience can be gained with both types of ashing, and the results of the two methods can be compared. Sodium results from this CAS No. Lanthanum chloride LaCl3 Irritant The limit of detection for sodium is 0. The limit of detection std. Ash analysis. Miller, D. Atomic absorption spec- Used to prepare ml solutions of each of troscopy, atomic emission spectroscopy, and inductively the concentrations listed in Table Each coupled plasma mass spectrometry. Wear used, likely with the same standard solutions and samples safety glasses and gloves during sample preparation.
Use acids in a hood. Shake well. Wet Ashing Supplies Note: Digestion procedure described is a wet digestion Used by students with nitric acid and hydrogen peroxide. Other types of digestion can be used instead. Accurately weigh out — mg of each digestion block sample and place in a digestion tube. Let the samples cool for at least 30 min. As soon as the reaction Sample Preparation: Liquid Samples starts, remove the tubes from the block, and 1.
Put an appropriate volume of liquid sample in let the reaction continue in the cooling rack. For a sports drink, Caution: Some sample types will have a use 0. Add 10 ml conc. Repeat Steps 8 and 9 for all the samples and the 3. Add deionized distilled dd water to volume. Put all the tubes in the digestion block, and 6. Make appropriate dilution of samples with leave until ca. Table If the tubes are left on the digestion 7. If necessary, filter samples using Whatman block too long and they become dry, remove, hardened ashless filter paper into container cool, and carefully add ca.
Turn off the digestion block when all the tubes have been Analysis digested and removed. Take appro- Table AAS, and the liquid or gas argon and the plasma in Analyze standards, reagent blanks, hardened ashless filter paper into container and samples. Accurately weigh out blended or ground ca.
Pre-dry sample over boiling water bath. Hg, for 16 h. Dissolve ash in 10 ml HCl solution , appropriate standard curve. Note: For the AAS samples, you need to subtract Standard Curve Data the liquid blank absorbance from the sports drink sample values, and the solid blank absorbance Potassium Standard Curves Sodium Standard Curves from the catsup and potato chip sample values.
If emission data are not Sample Data available for the samples, record the concentra- tions in ppm of sodium and potassium for the Atomic Absorption Spectroscopy food samples as analyzed i.
Show examples 2 of all calculations below the table. Cottage 1 chesse 2 Potato 1 chips 2 Questions 1. Compare the sodium and potassium values for catsup Inductively Coupled Plasma — Atomic Emission and potato chips to those reported in the U.
Describe how you would prepare the Na and K standard Liquid 1 — — — solutions for AES, using the ppm solutions of each, blank 2 — — — which are commercially available. If possible, all solutions Sports 1 for points in the standard curve should be made using drink 2 different volumes of the same stock solution. Do not use Solid 1 — — — volumes of less than 0. Make all standards to the same blank 2 — — — volume of ml. Note that each standard solution must Catsup 1 contain 10 ml conc.
Cottage 1 3. Describe how you would prepare a ppm Na solu- chesse 2 tion, starting with commercially available solid NaCl. Springer, New York 1. Use the standard curves from AAS and the plasma mass spectrometry. In: Nielsen SS ed absorption readings of the samples to deter- Food analysis, 4th edn. Such a solution is referred to as a standard solution. The assay for titratable acidity is a volumetric method that uses a standard solution and, most commonly, the Principle of Method indicator phenolphthalein.
In the titration, a standard solution of sodium hydroxide reacts with the organic A standard acid can be used to determine the exact acids present in the sample. The normality of the sodium normality of a standard base, and vice versa.
A standard acid such as potassium acid phthalate can be used to determine the exact normality CAS No. Hazards of the standard sodium hydroxide used in the titration. When colored Phenolphthalein Irritant solutions obscure the pink endpoint, a potentiomet- Potassium acid phthalate Irritant ric method is commonly used.
Springer, New York. Allow the water to cool with ascarite protection. Therefore, CO2-free water is prepared and used for standardizing acids and base and for determining Dissolve 1.
Put in bottle with titratable acidity. An ascarite trap is attached to bottles of eyedropper. While Use appropriate precautions in handling concentrated adding about 40 ml of dd water, stir the NaOH acid and base. Otherwise, adhere to normal laboratory pellets with a glass stirring rod. Continue safety procedures. Wear gloves and safety glasses at all stirring until all pellets are dissolved.
Quan- times. Waste may be put down the drain using a water titatively transfer the NaOH solution into rinse, but follow good laboratory practices outlined by a ml volumetric flask. Dilute to volume environmental health and safety protocols at your insti- with dd water.
The solution must be cooled tution. Store this solution in a plastic bottle and label Supplies appropriately. Prepare ca. Add ca. Standardize ca.
Record the exact weights. Add Equipment ca. Record the beginning and Calculations Required before Lab ending volume on the buret. Titration should proceed to the faintest tinge of pink that persists 1. Calculate how much NaOH to use to prepare for 15 s. Record the total volume of NaOH used Preface for definition of percent solutions.
Data from this part will 2. Calculate how much concentrated HCl to use be used to calculate the mean normality of the to prepare ml of ca. Remember that you have your stan- 1. To duplicate. Record the volumes used. Describe in detail how you standardized your ca. The range Determine the titratable acidity and pH of food samples.
Prepared as described in Method A. HCl ml Vol. Wear safety glasses at all times. Waste likely may be put down the drain using a water rinse, but follow good Questions laboratory practices outlined by environmental health 1. How would you and safety protocols at your institution. Describe how you prepared the ml of ca. Supplies Show your calculations. Also, observe any color changes that occur Equipment during the titration to determine when the phenol- phthalein endpoint is reached.
Sample B without phenolphthalein does not need to be followed with the pH meter, but is to be Procedure titrated along with the other beaker to aid in observing I. Soda color changes. Do at least duplicate determinations for unboiled soda Data and Calculations and for boiled soda sample; open soda well before use to allow escape of carbon dioxide so that the sample can I. Soda be pipetted.
Using the volume of NaOH used, calculate the titrat- 1. Unboiled soda: Pipette 20 ml of soda into a able acidity TA of each soda sample as percent- ml Erlenmeyer flask. Record the beginning and ending vol- umes on the buret to determine the total volume Buret Buret Vol.
Observe Rep start end titrant fades? TA the endpoint. Note whether the color fades. Boiled soda: Pipette 20 ml of soda into a ml Unboiled soda: Erlenmeyer flask. Bring the sample to boiling 1 on a hot plate, swirling the flask often. Boil the 2 sample only 30—60 s. Cool to room temperature. Add 3 drops of the phenolphthalein solution and titrate as Boiled soda: described above.
Observe the endpoint. Sample calculation: II. As an example, a small Procedure change in the amount of an ingredient may determine if a product can be labeled low fat. As a result, the abil- 1. Enter the ity to immediately approximate how a formulation Nutrition Labeling section of the program.
In some cases, the opposite situation may occur 2. Enter the ingredients for formula 1 listed in and a concept called reverse engineering is used.
In Table Click on the Add Ingredients button, reverse engineering, the information from the nutri- then select each ingredient from the ingredient list tional label is used to determine a formula for the window and click on the Add button, click on the X product. Caution must be used during reverse engi- to close the window after all ingredients have been neering.
In most cases, only an approximate formula added. Enter the percentage of each ingredient for for- vided by the nutritional label may be necessary. Enter the serving size common household unit described earlier. In this laboratory, you will use a and the equivalent metric quantity and number computer program to prepare a nutritional label from of servings.
First, click on the Serving Size button a product formula, determine how changes in the for- under Common Household unit, enter 8 in the window, mula affect the nutritional label, and observe an exam- click on OK, select oz from the units drop down list; ple of reverse engineering. Nutrition labeling. Nielsen Ed. Owl Software. Condensed skim milk Enter a name and save formula 1. From the yogurt formula 1. After contacting several suppliers, File menu, select Save Formula.
View the nutrition label and select label options. The composi- tein; the daily value footnote and calories conver- tion of the Dairy Calcium you will add is shown sion chart will be displayed unless Hide Footnote in Table Add and enter the name of the new ingredient 7. Edit the ingredient declarations list.
Click on the to the database. Answer yes to the question, top window and the ingredient declaration can be and click OK. Enter the new ingredient composition Table Copy and paste the nutritional label and ingredi- under the edit ingredient file tab, the row will turn ent declaration list for formula 1 in a Word file.
Edit the ingredient declaration which will paste the label, click Return on the label window. To appear on the ingredient list for the new copy and paste the ingredient list for formula 1, ingredient.
Click on the Return button. Component Amount Enter a name and save formula 2. Save the changes to the ingredient file. Click on View and print the nutritional label for the new the Finish Edit button, answer Yes to the question. Follow the 5. Select close ingredient file. Open food analysis formula 1 in the Formula handout. Development Section of the program. From You will have to perform this calcula- 7. Add the new Dairy Calcium ingredient tion yourself following the example in Step 8.
In this example, the program will automatically go through the reverse engineering process. Enter the amount of calcium required in the for- iron are entered. The minimum and maximum levels of each except skim milk and Dairy Calcium Find nutrient are calculated on a g basis. Comment: calcium in the Properties column and enter in The program uses the rounding rules to determine the the Minimum and Maximum columns for calcium.
This lets the program know that you want to have 3. The information about nutrient minimum and mg of calcium per g. In both the Min and maximums is transferred into the Formula Max columns of the formula ingredients enter Com- for milk 3.
This lets the program adjust the amount of skim milk 4. Ingredients used in the formula are then selected and Dairy Calcium calcium phosphate and based on the ingredient declaration statement on keeps the amount of all the other ingredients con- the nutrition label.
Comment: Selecting the right stant. Click on the Formulate button, click OK. Enter a name and save the modified formula. Restrictions on the amount of each ingredient the X to close the window, select Save Formula from in the formula are imposed whenever possible. Comment: This is a critical step that requires knowl- Open the new formula on the nutritional label- edge about the typical levels of ingredients used in the ing section.
Click on the Labeling Menu tab, select product. In this example, the amount of click open. Make sure you have the correct serving size gelatin is limited to 0. The program calculates an approximate formula. Assume you added enough Dairy Calcium to 7.
Comment: This information is yogurt? Make a nutrition label using the chocolate chip cookie section of the program accessed by selecting View recipe and other information in Table Conversion fac- Reverse Engineering Section then Label to Spec from tors to get the weight of sugars and salt can be found in the Reverse Engineering menu. Food analysis, 4th edn. Springer, New York 2. Background It is generally required that reported values minimally include the mean, a measure of precision, Volumetric glassware, mechanical pipettes, and balances and the number of replicates.
The number of are used in many analytical laboratories. If the basic significant figures used to report the mean reflects skills in the use of this glassware and equipment the inherent uncertainty of the value, and it needs are mastered, laboratory exercises are easier, more to be justified based on the largest uncertainty in enjoyable, and the results obtained are more accurate making the measurements of the relative precision of and precise.
Measures of accuracy and precision can the assay. The mean value is often expressed as part be calculated based on the data generated, given the of a confidence interval CI to indicate the range glassware and equipment used, to evaluate the skill of within which the true mean is expected to be found. Determining mass using an analytical balance is A procedure or instrument is generally not deemed the most basic measurement made in an analytical inaccurate if the CI overlaps the standard value.
Accurately weighing reagents is the first step needs improvement. In the case of testing the accuracy in preparing solutions for use in various assays. All analytical laboratories use volumetric coefficient of variation CV. Calculations of precision glassware and mechanical pipettes. Mastering their are largely independent of the number of replicates, use is necessary to obtain reliable analytical results. This laboratory includes of commonly used laboratory equipment.
However, assessment of the accuracy and precision of automatic for more general acceptance of procedures, they are pipettors. An example application is determining the validated by collaborative studies involving several accuracy of automatic pipettors in a research or qual- laboratories. Collaborative evaluations are sanctioned ity assurance laboratory, to help assess their reliability by groups such as AOAC International, AACC Inter- and determine if repair of the pipettors is necessary.
Such collaborative studies are prerequisite to pipettors to determine if they accurately dispense procedures appearing as approved methods in manu- the intended volume of water. To do this, water dis- als published by these organizations. Introduction to food analysis. S, Nielsen Ed. Evaluation of analytical data. Repeat this proce- Analysis, 4th ed.
Note that the total Familiarize, or refamiliarize, oneself with the use volume will be 60 ml. It is not necessary to of balances, mechanical pipettes, and volumetric empty the beaker after each pipetting. Do six determinations. Analytical balance and buret. Principle of Method a Repeat the procedure as outlined in Step 2a, Proper use of equipment and glassware in analytical but use a ml beaker, a ml or ml tests helps ensure more accurate and precise results.
It is not necessary to buret empty the beaker after each addition. Analytical balance and mechanical pipette. It is not necessary to empty the beaker after each pipetting.
Notes 5. Total content TC versus total delivery TD. Before or during the laboratory exercise, the instructor is Tare a ml volumetric flask on a top loading encouraged to discuss the following: 1 Difference between balance.
Fill the flask to the mark with water. Now tare a ml 2 difference between markings on a ml versus a or beaker and pour the water from the volumetric ml buret. Weigh the water delivered from the volumetric flask. Readability versus accuracy. Record the observed weight. Use gloves Record data in tables that follow.
Check the temperature of least two other top loading balances, recording the water with a thermometer. Analytical balance and volumetric pipettes.
Are these results consistent with what would be expected? In a titration experiment using a buret, would you expect to use much less than a ml volume in each titration? Which is a volumetric pipette? This laboratory was developed with inputs from Dr 7.
From your results from Part 6 of this lab, would you now Charles E. Carpenter, Department of Nutrition and assume that since a balance reads to 0. What sources of error human and instrumental were evident or possible in Parts 2—4, and how could these be reduced or eliminated?
You are considering adopting a new analytical method in your lab to measure the moisture content of cereal products. Nielsen SS Introduction to food analysis, Ch. Springer, New York and compare it to the old method? In: or estimate the accuracy of the new method?
Nielsen SS ed Food Analysis, 4th edn. Moisture is an important factor in food quality, preservation, and resistance to deterioration. Principle of Method Determination of moisture content also is necessary The sample is heated under specified conditions and to calculate the content of other food constituents on the loss of weight is used to calculate the moisture a uniform basis i. The dry matter content of the sample.
Instructors may want to have students compare results Near infrared X with and without these fiberglass covers. Moisture and total solids analysis, information, or record container information linker to Ch. Use gloves or tongs when handling sam- New York. These pans and crucibles have been dried and stored in desiccators prior to weighing.
Overall Objective They will pick up moisture by sitting on the counter, The objective of this experiment is to determine and so remove them from the desiccator only just before compare the moisture contents of foods by various use. Open desiccators slowly to avoid damage and methods of analysis.
After cooling in a desiccator, the crucibles containing I. Moisture in Corn Syrup ashed milk would be weighed and the ash content 1. Label dried pans disposable aluminum calculated. Place 5 g of sample in the pan and weigh IV. Moisture of Nonfat Dry Milk accurately. Because corn syrup is very 1. Weigh accurately the dried pan with lid.
Place 3 g of sample in the pan and weigh syrup. Store in a desiccator until samples are 4. Store in a desiccator until samples are weighed. Label dried pans disposable aluminum 1. Weigh accurately dried pan with lid. Note identifier number on pan and lid. Place 3 g of ground sample in the pan and 2. Place 2—3 g of sample in the pan and weigh weigh accurately. Be sure metal covers are ajar, to allow 4. Store in a desiccator until samples are water loss.
Remove from oven, realign covers to 5. Data and Calculations III. Note identified num- wt of wet sample ber on crucible. Label weighing pans i. Fresh basil 1 4. Store in a desiccator until samples are cooled 2 to ambient temperature. Label weighing pan, add 10 g dried sand and stirring rod, then weigh accurately.
Add 5 g of sample and weigh accurately. Mix with stirring rod being careful not to spill any of the Objective sample. Leave the stirring bar in the pan. Bleed dried air into the vacuum oven method, with and without the addition oven as vacuum is released. Store in a desiccator until samples are cooled to ambient temperature. Hazards Determine the moisture content of corn flour using a Toluene Harmful, highly flammable rapid moisture analyzer.
Continue refluxing until two consecutive readings 15 min apart show no change. Toluene is highly flammable and is harmful if Dislodge any water held up in the condenser inhaled. Use adequate ventilation. Wear safety glasses with a brush or wire loop. Rinse the condenser and gloves at all times. For disposal of toluene carefully with ca.
Dislodge any waste, follow good laboratory practices outlined by moisture droplets adhering to the Bidwell— environmental health and safety protocols at your Sterling trap or toluene trapped under the institution. For this, use the wire.
Rinse wire with a small amount 10 ml of toluene Supplies before removing from apparatus. Flask, condenser, and receiver must be scrupulously length with a T.
For example, the apparatus, including ling trap, T. No open flame! It should be long enough to extend the Bidwell—Sterling trap. Flatten the 2. A correction blank for toluene must be conducted loop on the buret brush and use this brush, periodically by adding 2—3 ml of distilled water to ml of toluene in the distillation flask, then inverted, as a wire to dislodge moisture drops following the procedure in Steps 2—6 above.
Data and Calculations Procedure 1. Grind the fresh basil with a small table-top food grinder. Pulse grind the sample in 5—10 s Wt. Avoid long pulses and excessive grinding to prevent frictional heat. Weigh approximately 40 g of sample basil or NFDM accurately amount chosen to yield 2—5 ml water. Transfer sample quantitatively to distilling flask. Add sufficient toluene to cover the sam- Objective ple completely not less than 75 ml.
Assemble the apparatus as shown in Chap. Fill the trap with toluene flour by the Karl Fischer KF method. Insert a loose nonabsorbing cotton When the sample is titrated with the KF reagent, plug into the top of the condenser to prevent which contains iodine and sulfur dioxide, the iodine condensation of atmospheric moisture in the is reduced by sulfur dioxide in the presence of water condenser.
The water reacts stoichiometri- 5. Bring to boil and reflux at about two drops per cally with the KF reagent. The volume of KF reagent second until most of the water has been col- required to reach the endpoint of the titration visual, lected in the trap, then increase the reflux rate conductometric, or coulometric is directly related to to ca. Hazards several samples exact number depends on type Karl Fischer reagent Toxic of sample.
Remember that this entire appara- 2-Methoxyethanol tus is very fragile. To prevent contamination Pyridine from atmospheric moisture, all openings must Sulfur dioxide be closed and protected with drying tubes.
Iodine Harmful, dangerous to the environment II. Normally, this needs to be done only once a day, or when changing the KF reagent supply. Reagents 1. Put the magnetic stir bar in the vessel and for 2 h turn on the magnetic stirrer. Remove the caps if any from drying tube. Hazards, Cautions, and Waste Disposal Turn the buret stopcock to the filling posi- tion.
Hold one finger on the air-release hold Use the anhydrous methanol in an operating hood in the rubber bulb and pump the bulb to fill since the vapors are harmful and it is toxic. Otherwise, the buret.
Close the stopcock when the KF adhere to normal laboratory safety procedures. Use reagent reaches the desired level at posi- appropriate eye and skin protection.
The KF reagent tion 0. Titrate the water in the solvent anhydrous hazardous wastes. Allow the solution to stabilize at the Equipment endpoint on the meter for at least 1 min before proceeding to the next step. Berkeley, CA, Aquametry Apparatus 6. Fill the buret with the KF reagent, then titrate the water in the sodium tartrate Procedure dihydrate sample as in Step II. Record the Instructions are given as for a nonautomated unit, and volume ml of KF reagent used.
If using an automated unit, 7. Calculate the KF reagent water moisture follow instructions of the manufacturer.
Prepare samples for analysis and place in S reaction vessel as described below. Use an extra Volume piece of weighing paper to form a cone- Wt.
Moisture content of samples by Karl Fischer method: If any samples analyzed are in liquid form: — Use a 1-ml syringe to draw up about 0. Weigh the syringe with sample Wt. The color of the solution in the vessel should change to Principle light yellow and the meter will register Specific frequencies of infrared radiation are absorbed below the KF zone on the meter.
Fill the buret, then titrate the water in the the —OH stretch of the water molecule. The concen- sample as in Step II. Record the tration of moisture in the sample is determined by volume ml of KF reagent used. To titrate another sample, repeat Steps II. After titrating energy absorbed. Explain your answers. For each method, what would you have to do to the corn flakes Follow instructions from manufacturer for use of the before measuring the moisture content?
You have been asked to Data and Calculations evaluate the feasibility of switching to new methods the specific one would depend on the product for measuring moisture content.
In separate tables, summarize the results from the various What disadvantages or potential problems might methods used to determine the moisture content of each you encounter with the other two methods? This experiment was developed in part with 2. Calculate the moisture content of the liquid milk samples materials provided by Dr Charles E. Montecalvo, Jr. Arizona Instrument Corp. Why was the milk sample partially evaporated on a hot plate before being dried in the hot air oven?
Of the various methods used to measure the moisture 11th edn. Paul, MN content of corn syrup, based on concerns for accuracy AOAC International Official methods of analysis, and precision, what method would you choose if you 18th edn, ; Current through revision 2, On-line. In: 5. What is the difference between moisture content and Nielsen SS ed Food analysis, 4th edn. Springer, New York water activity measurements?
What method would you use to measure the moisture examination of dairy products, 17th edn. Solvent drips onto the sample and soaks it to extract the fat. At 15—20 min Background intervals, the solvent is siphoned to the heating flask, to start the process again. Chemicals The lipid content of a food determined by extraction with one solvent may be quite different from the lipid content as determined with another solvent of differ- CAS No. Hazards ent polarity.
Fat content is determined often by solvent extraction methods e. The method of choice depends on a variety of factors, including the nature of the sample Hazards, Precautions, and Waste Disposal e. Otherwise, adhere to normal This experiment includes the Soxhlet, Goldfish, laboratory safety procedures.
Wear gloves and safety Mojonnier, and Babcock methods. If samples analyzed glasses at all times. Petroleum ether and ether liquid by these methods can be tested by an instrumen- wastes must be disposed of in designated hazardous tal method for which equipment is available in your waste receptacles.
Snack foods are suggested for analysis and compari- Supplies son by the Soxhlet and Goldfish methods, and milk by the Mojonnier and Babcock methods. Fat analysis. Wearing plastic gloves, remove three predried cellulose extraction thimbles from the desic- Data from moisture analysis: cator.
Place the three samples in a Soxhlet extractor. Cool dried samples in a desiccator then 1 reweigh. The Soxhlet extraction procedure utilized petroleum ether. What were the advantages of using the Soxhlet extraction Name of Snack Food: method rather than the Goldfish extraction method?
Solvent continuously Rep g Thimble g wool g g wool g drips through the sample to extract the fat. Fat con- 1 tent is measured by weight loss of sample or weight 2 of fat removed. Follow Steps 1—4 in Soxhlet procedure. Place the thimble in the Goldfish condenser bracket. Push the thimble up so that only about 1 cm. Follow Steps 6 and 7 in Soxhlet procedure.
If the fat content 1. What would be the advantages of using ethyl ether rather of the food you analyzed was given on the label, report than petroleum ether in a solvent extraction method, such this theoretical value.
Label serving size g : 3. Make triplicate determinations on both the sample and reagent blanks. The Principle procedure given here is for fresh milk. Other samples may need to be diluted with distilled water in step 2 and require Fat is extracted with a mixture of ethyl ether and petro- different quantities of reagents in subsequent steps. Consult leum ether. The extract containing the fat is dried and the instruction manual or AOAC International Official Methods expressed as percent fat by weight.
The assay uses not only ethyl ether and petroleum ether, but also ammonia and ethanol. Ammonia dis- Procedure solves the casein and neutralizes the acidity of the Instructions are given for analysis in triplicate.
Ethanol prevents gela- tion of the milk and ether, and aids in the separation 1. Turn on power unit and temperature controls of the ether—water phase. Ethyl ether and petroleum for oven and hot plate on the fat side of the ether serve as lipid solvents, and petroleum ether Mojonnier unit.
Warm milk samples to room temperature and mix well. Chemicals 3. CAS No. Hazards Handle dishes from this point on with tongs or gloves. Use three dishes for each type of milk Ammonium Corrosive, dangerous for the samples, and two dishes for the reagent blank. Cool dishes in cooling desiccator for 7 min.
Ethanol Highly flammable 5. Weigh dishes, record weight of each dish and its Petroleum Harmful, highly flammable, identity, and place dishes in desiccator until use. Weigh samples accurately ca. If weighing rack is used, fill curved pipettes and place in rack on the balance. Weigh Hazards, Precautions, and Waste Disposal each sample by difference.
Add chemicals for the first extraction in the Ethanol, ethyl ether, and petroleum ether are fire haz- order and amounts given below. After each ards; avoid open flames, breathing vapors, and contact addition of chemicals, stopper the flask and with skin.
Ether is extremely flammable, is hygro- shake by inverting for 20 s. Ammonia is a corrosive; avoid contact and breathing vapors. Oth- erwise, adhere to normal laboratory safety procedures. First extraction Second extraction Wear gloves and safety glasses at all times.
Petroleum Chemicals Step Amount ml Step Amount ml ether and ether liquid wastes must be disposed of in designated hazardous waste receptacles. The aqueous Ammonia 1 1. Carefully pour off the ether solution of each Notes sample into a previously dried, weighed, and Reagents must be added to the extraction flask in the follow- cooled fat dish. Most or all of the ether layer ing order: water, ammonia, alcohol, ethyl ether, and petroleum should be poured into the dish, but none of the ether.
The burets on the dispensing cans or tilting pipets are remaining liquid must be poured into the dish. List possible causes for high and low results in a Mojon- Repeat the extraction procedure a second nier fat test. How would you expect the elimination of alcohol from the following the sequence and amount given in Mojonnier procedure to affect the results?
Again, after each addition 3. How would you propose to modify the Mojonnier procedure of chemicals, stopper the flask and shake by to test a solid, nondairy product? Explain your answer. Centrifuge the flasks again, as described above. If this is done, repeat the Principle centrifugation. Sulfuric acid is added to a known amount of milk Pour ether extract into respective fat dish sample in a Babcock bottle.
The acid digests the pro- i. Centrifugation poured into the same fat dish used for that and hot water addition isolate the fat into the graduated sample from the first extraction , taking care neck of the bottle. The Babcock fat test uses a volumetric to remove all the ether but none of the other measurement to express the percent of fat in milk or liquid in the flask. Complete the evaporation of ether, either very carefully on the hot plate this can be problem- Note atic and a fire hazard or open in a hood.
The specific gravity of liquid fat at that temperature is not fast enough to cause splattering. If the approximately 0. The calibration on the gradu- plate appears to be too hot and boiling is too ated column of the test bottle reflects this fact and enables one fast, only part of the dish should be placed to make a volumetric measurement, which expresses the fat on the hot plate.
If instead using an operating content as percent by weight. Chemicals When all the ether has been evaporated from the dishes, place the dishes in the vacuum CAS No.
Sulfuric acid Corrosive Cool the dishes in the desiccator for 7 min. Accurately weigh each dish with fat. Record weight. Hazards, Precautions, and Waste Disposal Concentrated sulfuric acid is extremely corrosive; avoid Data and Calculations contact with skin and clothes and breathing vapors.
Calculate the fat content of each sample. Subtract the Wear gloves and safety glasses at all times. Otherwise, average weight of the reagent blank from the weight of adhere to normal laboratory safety procedures. Sulfuric each fat residue in the calculation. Fit the dis- Reagent penser with a thin, semirigid tube to dispense directly Blank A — and deep into the Babcock bottle while mixing con- Blank B — tents. Add glymol red reader to top of fat layer. Equipment Immediately use a divider or caliper to mea- sure the fat column to the nearest 0.
Procedure 9. Reject all tests in which the fat column is milky Instructions are given for analysis in triplicate.
Adjust milk sample to ca. The fat should be clear and spar- homogenous. Using a standard milk pipette, kling, the upper and lower meniscus clearly pipette After the pipette has emptied, blow out should be clear. Record the readings of each test and determine bottle. Allow milk samples to adjust to ca.
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