A: Infrared Absorption 197K.

B: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

Standard stock solution— Dissolve an accurately weighed quantity of USP Dimethyl Sulfoxide RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 1.0 mg of USP Dimethyl Sulfoxide RS per mL.

Sensitivity check solution— Dilute the Standard stock solution with methanol to obtain a solution having a concentration of 2.0 µg per mL.

System suitability solution— In a 50-mL volumetric flask, dissolve 20 mg of USP Methylsulfonylmethane RS in 5 mL of the Standard stock solution, dilute with methanol to volume, and mix to obtain a solution having a known concentration of about 0.1 mg of USP Dimethyl Sulfoxide RS per mL and 0.4 mg of USP Methylsulfonylmethane RS per mL.

Test solution— Transfer about 100 mg of methylsulfonylmethane, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with methanol to volume, and mix. Sonicate at 50 for 1 minute, allow to cool to room temperature, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.53-mm × 30-m capillary column coated with a 5-µm phase G2. The column temperature is maintained at 120. Helium is used as the carrier gas, flowing at a rate of 5.0 mL per minute. The split ratio is 2:1. The injection port temperature is maintained at 250, and the detector temperature is maintained at 250. Chromatograph the Sensitivity check solution: the dimethyl sulfoxide peak must be greater than 10 times the noise height, the noise height being determined by a suitable procedure. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between dimethyl sulfoxide and methylsulfonylmethane is not less than 2.0.

Procedure— Inject a volume (about 1 µL) of the Test solution into the chromatograph, record the chromatogram, and measure the responses for the major peaks. Calculate the percentage of each impurity in the portion of Methylsulfonylmethane taken by the formula: in which ri is the response of each individual impurity in the chromatogram of the Test solution; and rs is the sum of the responses of all of the peaks other than the solvent peak: not more than 0.1% of dimethyl sulfoxide is found; not more than 0.05% of any other individual impurity is found; and the sum of all impurities, including dimethyl sulfoxide, is not more than 0.2%.

Diluent— Transfer about 950 mL of methanol to a 1-L volumetric flask. Add 0.60 mL of di(ethylene glycol) methyl ether, and dilute with methanol to volume.

Standard preparation— Dissolve an accurately weighed quantity of USP Methylsulfonylmethane RS in Diluent, and dilute quantitatively, and stepwise if necessary, with Diluent to obtain a solution having a known concentration of about 0.4 mg per mL. Sonicate at 50 for 1 minute, allow to cool to room temperature, and mix.

Assay preparation— Transfer about 40 mg of Methylsulfonylmethane, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with Diluent to volume, and mix. Sonicate at 50 for 1 minute, allow to cool to room temperature, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.53-mm × 30-m capillary column coated with a 5-µm phase G2. The column temperature is maintained at 120. Helium is used as the carrier gas, flowing at a rate of 5.0 mL per minute. The split ratio is 2:1. The injection port and detector temperatures are maintained at 250. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C2H6O2S in the portion of Methylsulfonylmethane taken by the formula: in which C is the concentration, in mg per mL, of USP Methylsulfonylmethane RS in the Standard preparation; and RU and RS are the peak response ratios of methylsulfonylmethane to di(ethylene glycol) methyl ether obtained from the Assay preparation and the Standard preparation, respectively.