Packaging and storage—
Preserve in tight, light-resistant containers.
Identification—
B:
Add 1.5 mL cautiously and dropwise to 2.5 mL of hydriodic acid in a test tube cooled in ice. Filter the mixture rapidly, and collect the precipitate. Dry the precipitate in vacuum: a deep violet, crystalline solid is obtained, and it is soluble in chloroform, yielding a red solution.
Acidity—
Dissolve 50.0 g in 100 mL of water, and add phenolphthalein TS. If the solution remains colorless, titrate with 0.01 N sodium hydroxide until a pink color appears: not more than 5.0 mL of 0.01 N sodium hydroxide is consumed.
Water, Method I 
921
:
not more than 0.1%.
[NOTE—Weigh and transfer the test specimen in an environment of low humidity to minimize absorption of atmospheric water.
]
Ultraviolet absorbance—
Maintain Dimethyl Sulfoxide in a water bath at a temperature of less than 20
[NOTE—Do not freeze.
], and purge with dry nitrogen for 30 minutes. Record the UV absorption spectrum between 270 and 350 nm in a 1-cm cell, using water as the blank: the spectrum is smooth with no absorption maxima; the absorbance at 275 nm is not more than 0.20, and the absorbance ratios,
A285/
A275 and
A295/
A275, at the wavelengths indicated by the subscripts, are not more than 0.65 and 0.45, respectively.
Substances darkened by potassium hydroxide—
Add 0.5 mL of water and 1.0 g of solid potassium hydroxide to 25 mL of Dimethyl Sulfoxide in a glass-stoppered, 50-mL flask. [NOTE—Use only solid potassium hydroxide that is white with no discoloration.] Insert the stopper, and heat in a steam cone for 20 minutes. Cool to room temperature: the absorbance of the solution at 350 nm, measured in a 2-cm cell, water being used as the blank, does not exceed 0.046.
Limit of dimethyl sulfone—
System suitability solution—
Prepare a solution containing about 0.15 mg of dimethyl sulfone per mL and 0.1 mg of dibenzyl per mL in Dimethyl Sulfoxide.
Chromatographic system—
The gas chromatograph is equipped with a flame-ionization detector and a suitable recorder, and contains a 3-mm × 1.5-m column packed with 10% liquid phase G25 on support S1A (see
Chromatography 621). The column temperature is programmed to change at a rate of about 10
per minute from 100
to 170
, the injection port is maintained at a temperature of about 210
, and the detector block is maintained at a temperature of about 220
. Helium is used as the carrier gas, flowing at the rate of about 30 mL per minute. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the column efficiency as determined from the dimethyl sulfoxide peak is not less than 1000 theoretical plates; and the resolution,
R, between the dimethyl sulfone and dibenzyl peaks is not less than 5.0.
Procedure—
Inject about 1 µL of Dimethyl Sulfoxide into the gas chromatograph, record the chromatograms, and measure the responses of the peaks: the response of any peak, other than that of dimethyl sulfoxide, is not greater than 0.03% of the total of the responses of all of the peaks; and the total of the responses of all secondary peaks is not greater than 0.1% of the total of the responses of all of the peaks.
Limit of nonvolatile residue—
Evaporate 50 g in a rotary evaporator at a pressure of about 30 mm of mercury at 95
. Wash the residue from the evaporator flask into a tared dish with several 25-mL portions of glass-distilled methanol, and evaporate on a hot plate in an exhaust hood: the weight of the residue does not exceed 5.0 mg.
;)
