MIL-PRF-23942A(AS)
Water, percent by weight = (mL Karl Fischer reagent)(titer)(100)
grams sample
Duplicate results by the same operator shall not differ by more than 5 ppm.
4.5.9 Antioxidant determination.
4.5.9.1 Apparatus.
a. A mixing device capable of rotating the sample vials end over end at 50 rpm.
b. Ultraviolet spectrophotometer, the Beckman Model DU or an equivalent instrument.
c. 40 mL vials with plastic screw caps equipped with TFE liners or equivalent.
d. Volumetric glassware.
4.5.9.2 Reagents and materials. All reagents shall conform to the specifications established
by the Committee on Analytical Reagents of the American Chemical Society.
a. Antioxidant.
b. Cyclohexane, Spectro grade.
c. Potassium hydroxide, alcoholic solution prepared by dissolving 28.05 g of potassium
hydroxide in 500 mL of methanol, then filter the solution through glass fiber filter paper to
remove the insoluble carbonates.
4.5.9.3 Procedures.
4.5.9.3.1 Calibration curve. Weigh 1.0 g accurate to ±1 mg of the same brand and grade of
antioxidant used in the plant process into a weighing bottle. Dissolve the antioxidant in
cyclohexane and quantitatively transfer to a 1-L volumetric flask, rinsing the weighing bottle
three times with cyclohexane. Dilute to volume with cyclohexane and mix well. Pipet 1, 2, 3,
and 4 mL of the standard antioxidant solution into separate 50-mL volumetric flasks and dilute to
volume with alcoholic potassium hydroxide. The resulting solutions contain 20, 40, 60, and 80
µg/mL of antioxidant. Measure the absorbance of each of the standards in a 1 cm cell versus
alcoholic potassium hydroxide at wave lengths of 308, 330, and 292 nanometers (nm). Compute
the differential absorbance as follows:
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