Fatty acid composition—
Place about 1 g of Oil in a small conical flask fitted with a reflux attachment. Add 10 mL of methanol and 0.5 mL of 1 N methanolic potassium hydroxide solution prepared by dissolving 34 g of potassium hydroxide in sufficient methanol to produce 500 mL, allow to settle for 24 hours, and decant the clear solution. Reflux the mixture for 10 minutes, cool, transfer to a separator with the aid of 15 mL of
n-heptane, shake with 10 mL of saturated sodium chloride solution, and allow to separate. Transfer the lower layer to another separator, and shake it with 10 mL of
n-heptane. Wash the combined organic layers with 10 mL of water, dry over anhydrous sodium sulfate, and filter. Introduce a suitable portion of the filtrate into a gas chromatograph equipped with a flame-ionization detector and a column, preferably glass, 1.5 m in length and 4 mm in internal diameter packed with 10% liquid phase G4 on support S1A, maintained at a temperature of 175
. The carrier gas is nitrogen. Measure the 4 main peak areas of the methyl esters of the fatty acids. The order of elution is palmitate, stearate, oleate, and linoleate, and their relative areas, expressed as percentages of the total area of the 4 main peaks, are in the ranges 2 to 10, 1 to 10, 7 to 42, and 72 to 84, respectively.
Peroxide—
Mixed solvent—
Mix 60 mL of glacial acetic acid with 40 mL of chloroform.
Potassium iodide solution—
Prepare a saturated solution of potassium iodide in freshly boiled and cooled water, and store it protected from light. Discard it if it gives a color on addition of Mixed solvent and starch TS.
Procedure—
Transfer about 10 g of Oil, accurately weighed, to a conical flask, add 30 mL of
Mixed solvent, swirl to dissolve, add 0.5 mL of
Potassium iodide solution, swirl the flask for 1 minute, accurately timed, add 30 mL of water, and titrate with 0.01 N sodium thiosulfate VS, with vigorous agitation, to a light yellow color. Add 0.5 mL of starch TS, and continue the titration until the blue color has disappeared. Perform a blank test, and make any necessary correction. Calculate the peroxide content, in mEq per kg, by the formula:
1000VN / W,
in which
V is the volume, in mL, of sodium thiosulfate required, N is its normality, and
W is the weight, in g, of Oil taken. The limit is 10.0.
401
—
The free fatty acids in 10 g require for neutralization not more than 2.5 mL of 0.020 N sodium hydroxide.