A: Infrared Absorption 197F.

B: Standard stock solution 1—Transfer 50 mg of USP Diethylene Glycol RS, accurately weighed, to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Internal standard solution— Transfer 100 mg of 2,2,2-trichloroethanol (internal standard), accurately weighed, to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Standard stock solution 1— Transfer 50 mg of USP Diethylene Glycol RS, accurately weighed, to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Standard stock solution 2— Transfer 50 mg of USP Ethylene Glycol RS, accurately weighed, to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Standard stock solution 3— Transfer 50 mg of USP Glycerin RS, accurately weighed, to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Standard solution— Transfer 5.0 mL each of Standard stock solution 1, Standard stock solution 2, and the Internal standard solution to a 100-mL volumetric flask, and dilute with methanol to volume, and mix.

Resolution solution— Transfer 500 mg of USP Glycerin RS to a 10-mL volumetric flask, add 0.5 mL each of Standard stock solution 1 and Standard stock solution 2, dilute with methanol to volume, and mix.

Test solution— Transfer about 5 g of Glycerin to a 100-mL volumetric flask, add 5.0 mL of Internal standard solution, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector, a 0.53-mm × 30-m fused-silica analytical column coated with 3.0-µm G43 stationary phase. The injection port temperature is maintained at 220 and the detector temperature is maintained at 250. The carrier gas is helium, flowing at a rate of about 4.5 mL per minute. The split flow ratio is about 10:1. The chromatograph is programmed as follows. Initially, the column temperature is equilibrated at 100 for 4 minutes, then increased at a rate of 50 per minute to 120, and is maintained at 120 for 10 minutes then increased at a rate of 50 per minute to 220, and is maintained at 220 for 6 minutes. Chromatograph the Standard solution, and record the peak response ratio and retention times as directed for Procedure: the relative retention times are about 0.3 for ethylene glycol, 0.8 for diethylene glycol, and 1.0 for glycerin; the relative standard deviation for replicate injections for the diethylene glycol is not more than 10%; and the limit of quantitation of diethylene glycol and ethylene glycol is not more than 0.025%.

Procedure— Separately inject equal volumes (about 1 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the ethylene glycol and diethylene glycol peaks. Calculate the percentage of diethylene glycol and ethylene glycol in the portion of Glycerin taken by the formula: in which CS is the concentration, in mg per mL, of diethylene glycol (or ethylene glycol) in the Standard solution; CU is the concentration, in mg per mL, of Glycerin in the Test solution; and RU and RS are the peak response ratios for diethylene glycol (or ethylene glycol) to the internal standard peak obtained from the Test solution and the Standard solution: NMT the limit of quantitation for each, is found (0.025%).

Sodium periodate solution— Dissolve 60 g of sodium metaperiodate in sufficient water containing 120 mL of 0.1 N sulfuric acid to make 1000 mL. Do not heat to dissolve the periodate. If the solution is not clear, pass through a sintered-glass filter. Store the solution in a glass-stoppered, light-resistant container. Test the suitability of this solution as follows. Pipet 10 mL into a 250-mL volumetric flask, dilute with water to volume, and mix. To about 550 mg of Glycerin dissolved in 50 mL of water add 50 mL of the diluted periodate solution with a pipet. For a blank, pipet 50 mL of the solution into a flask containing 50 mL of water. Allow the solutions to stand for 30 minutes, then to each add 5 mL of hydrochloric acid and 10 mL of potassium iodide TS, and rotate to mix. Allow to stand for 5 minutes, add 100 mL of water, and titrate with 0.1 N sodium thiosulfate, shaking continuously and adding 3 mL of starch TS as the endpoint is approached. The ratio of the volume of 0.1 N sodium thiosulfate required for the glycerin–periodate mixture to that required for the blank should be between 0.750 and 0.765.

Procedure— Transfer about 400 mg of Glycerin, accurately weighed, to a 600-mL beaker, dilute with 50 mL of water, add bromothymol blue TS, and acidify with 0.2 N sulfuric acid to a definite green or greenish yellow color. Neutralize with 0.05 N sodium hydroxide to a definite blue endpoint, free from green color. Prepare a blank containing 50 mL of water, and neutralize in the same manner. Pipet 50 mL of the Sodium periodate solution into each beaker, mix by swirling gently, cover with a watch glass, and allow to stand for 30 minutes at room temperature (not exceeding 35) in the dark or in subdued light. Add 10 mL of a mixture of equal volumes of ethylene glycol and water, and allow to stand for 20 minutes. Dilute each solution with water to about 300 mL, and titrate with 0.1 N sodium hydroxide VS to a pH of 8.1 ± 0.1 for the specimen under assay and 6.5 ± 0.1 for the blank, using a pH meter. Each mL of 0.1 N sodium hydroxide, after correction for the blank, is equivalent to 9.210 mg of C3H8O3.