The following limit test is provided as a general procedure, when specified in the individual monographs for the gas chromatographic determination in compendial articles of traces of dimethylaniline, a hydrochloric acid scavenger that may have been carried over during processing.
Internal Standard Solution Unless otherwise specified in the individual monograph, prepare a solution of naphthalene in cyclohexane containing about 50 µg per mL.
Standard Preparation Unless otherwise specified in the individual monograph, transfer 50.0 mg of N,N-dimethylaniline to a 50-mL volumetric flask, add 25 mL of 1 N hydrochloric acid, swirl to dissolve, dilute with water to volume, and mix. Transfer 5.0 mL of the resulting solution to a 250-mL volumetric flask, dilute with water to volume, and mix. To a suitable centrifuge tube add 1.0 mL of this solution, 5.0 mL of 1 N sodium hydroxide, and 1.0 mL of Internal Standard Solution, shake vigorously for 1 minute, and centrifuge. Use the clear supernatant as the Standard Preparation.
Test Preparation Unless otherwise specified in the individual monograph, transfer 1.0 g of the substance to be tested to a suitable centrifuge tube, add 5 mL of 1 N sodium hydroxide, swirl to dissolve the specimen, add 1.0 mL of Internal Standard Solution, shake vigorously for 1 minute, and centrifuge. Use the clear supernatant as the Test Preparation.
Chromatographic System (see Chromatography 621) The gas chromatograph is equipped with a flame-ionization detector and a 2-mm × 2-m column packed with 3% liquid phase G3 on silanized packing S1A and is maintained at 120. Nitrogen is used as the carrier gas, flowing at the rate of about 30 mL per minute.
Procedure Inject equal volumes (within the range of 2 µL to 20 µL) of the Standard Preparation and the Test Preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. The ratio of the response of any dimethylaniline peak to the response of the naphthalene peak obtained from the Test Preparation is not greater than that obtained from the Standard Preparation (0.002%).