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FST 202 FOOD ANALYSIS

1. Directions and guidelines for using volumetric glasswaresVolumetric glasswares are precision glasswares capable of measurements of volume that are good to foursignificant digits and are consequently expensive. They are characterized by long slender necks with a singlegraduation mark on them. Any glassware with several graduation marks is not volumetric.

a. Maintenance and storage:i. Do not expose any volumetric glassware to sources of heat since such exposure will

adversely affect the calibration, do not dry any volumetric glassware in a drying oven.ii. Clean the glassware before using. It must drain in such a manner that a smooth film of

solution adheres to the inside, there must be no beading or droplet formation on the insidewalls of the vessel. Ensure beading is eliminated by using either of:

a) A mixture of equal parts of a saturated solution of potassium dichromate and conc.sulfuric acid.

b) A mixture of equal parts of 30g/l solution of potassium permanganate (KmnO4) anda 1mol/l solution of sodium hydroxide (NaOH). Removed the resulting residue ofMnO2 with dilute HCl or oxalic acid.

Rinse with distilled water and ascertain if the walls are sufficiently clean otherwise, repeatthe procedure.

b. Handling and use:i. Before use, rinse at least twice with small portions of the solution to be measured. When

filling, the rising liquid meniscus shall not change shape i.e. it shall not crinkle at its edges.After over-filling and drawing a little liquid, the meniscus shall be smoothly concave andnot crinkle at the edges.

ii. When using a volumetric flask, dilute the solution stepwise.a) Add the solution to be diluted into the flask, and add the diluent (usually distilled water)

to fill the flask about two-thirds. Ensure that any reagent on the ground glass lip isrinsed down. Swirl the flask to obtain utmost mixing or dissolution. Add the diluent sothat the bottom of the meniscus is even with the middle of the calibration mark at eyelevel.

b) If there are any droplets of water on the neck of the flask above the meniscus, blotthese out with a tissue paper. Dry the ground-glass stopper joint.

c) The solution is then thoroughly mixed. Keeping the stopper on securely by using thethumb or palm of the hand, invert the flask and swirl or shake it vigorously for 5 or 10seconds. Turn right-side up and allow the solution to drain from the neck of the flask.Repeat 10 times.

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iii. Do not shake or blow out volumetric pipets since its design allow retention of the tipvolume.

iv. In delivering hold the pipette vertically with the tip touching the side of the vessel to allowsmooth delivery without splashing and so that the proper volume will be left in the tip.

2. Procedures on determining proximate composition of foodDetermining proximate composition of food is analysis of foods and feedstuff for protein, fat, mineral salts,and soluble carbohydrate calculated by subtracting these values from the total. To carry out the analysis:

a. Set the protocol.b. Sample the food.c. Prepare the sample in readiness for extraction of the chosen analyte or compound of interest

(COI). Includes such processes as grinding, digestion, and centrifugation. The stage includesstandardisation.

d. Extract the COI, making available a less complex, and usually more concentrated compound orsubstance of interest via physical, chemical, or biochemical methods.

e. Separate from, or remove substances interfering with the detection of the COI in the extract. Thestep is conducted by chromatographic and electrophoretic processes where the main objective isnot to remove or extract something for further stages of analysis, but to finally resolve componentsof mixtures for detection and identification.

f. Detection (recognition or visualisation), and identification and/or quantification of the COI. Theprocess is characterized by signal recorded when a component of the sample is registered

(recognised, standardised or calibrated) above a base line, and the signal content is converted intoqualitative or quantitative information.

3. Proper use of pH penA pH pen is actually a portable pH electrode, encased in chemical resistant plastic, usually powered withbattery, and equipped with a digital display. It does not have a temperature compensator and is usedcommonly for field analytical work.

a. As in table-type pH meter, the electrode must first be calibrated before daily use, with Buffer 7,then Buffer 4 if sample is acidic or Buffer 10 if sample is basic.

b. After calibration, rinse the electrode with distilled water. Pat dry the excess liquid with cleantissue paper.

c. Rinse with the sample to be analyzed by immersion in small amount of sample and discard.d. Proceed with analysis of the sample by swirling gently until electrode output has stabilized.

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e. After each use, rinse with distilled water. Pat dry the excess liquid with tissue paper and let air-dry before storing in its hard plastic jacket.

References:

Shugar, Ballinger, and Dawkins, Chemical Technicians Ready Reference Handbook, p. 565-571

2010, Maryland Science Safety Manual, Chemicals: Managing, Handling, and Disposing

2010, Royal Society of Chemistry, London

2010, Ulrich de la Camp & Oliver Seeley, Helpful Hints in Use of Laboratory Equipment

2003, Reagecon Diagnostics Ltd.

GFS Chemicals, www.gfschemicals.com/