MIL-PRF-23942A(AS)
W = Weight of sample in grams.
45.02 = molecular weight of the carboxyl group, COOH.
Duplicate determinations shall not differ from the mean by more than ±0.05 percent carboxyl in
the range of 0.1 to 5.0 weight percent.
4.5.6 Unsaturation determination. The determination of unsaturation shall be as follows:
4.5.6.1 Apparatus.
a. Infrared spectrophotometer. Use a double beam instrument. Although a Perkin-Elmer
Model 21 or its equivalent is preferred, one of the less expensive instruments such as Infracord
or the IR-5 may be used with some sacrifice in reproducibility. ASTM-E275 may be used to
compare the performance of the equivalent spectrophotometer unit to the Perkin-Elmer Model
21.
b. Sample cells. Use two matched pairs of cells with sample cell thickness of 1,500 and 500
micrometers (µm). Build these cells in a laboratory if no commercial product is available.
Directions for preparation of the cells are given in 4.5.6.3a.
c. Accessory equipment.
(1) Vacuum desiccator
(2) Vacuum pump
(3) 25-mL volumetric flasks
4.5.6.2 Reagents and materials. Unless otherwise specified below, all reagents shall
conform to the specifications established by the Committee on Analytical Reagents of the
American Chemical Society (ACS).
a. Carbon disulfide.
b. Antioxidant. Phenyl-B-naphthylamine (PBNA).
4.5.6.3 Procedure.
a. Preparation of sample cells. Use pairs of infrared cells. One cell, of known thickness,
serves as the sample cell, while the other should be of the thickness to compensate for the carbon
disulfide solvent in the sample cell. If built in a laboratory, first build a sample cell of the latter
thickness, and then build several cells 2.5 percent thinner. Obtain differential spectra between a
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