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5.16 N,N-DIMETHYLANILINE (DIMETHYLANILINE)

 ​           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 N,N-dimethylaniline, a hydrochloric acid scavenger that may have been carried over during processing.

 ​           Carry out the determination by gas chromatography, Appendix 3.4, using naphthalene as the internal standard.

 ​           Internal standard solution Unless otherwise specified in the individual monograph, dissolve 50 mg of naphthalene in cyclohexane and dilute to 50 ml with the same solvent. Dilute 5 ml of this solution to 100 ml with cyclohexane.

 ​            Standard solution Unless otherwise specified in the individual monograph, transfer 50.0 mg of N,Ndimethylaniline to a 50-ml volumetric flask, add 2 ml of hydrochloric acid and 20 ml of water, shake to dissolve and dilute to volume with water. Dilute 5.0 ml of this solution to 250.0 ml with water. To 1.0 ml of the latter solution in a ground-glass-stoppered tube add 5 ml of 1 M sodium hydroxide and 1.0 ml of the Internal standard solution. Stopper the tube and shake vigorously for 1 minute. Centrifuge if necessary and use the upper layer.

 ​           Test solution Unless otherwise specified in the individual monograph, transfer 1.00 g of the test substance to a ground-glass-stoppered tube, add 5 ml of 1 M sodium hydroxide and 1.0 ml of the Internal standard solution. Stopper the tube and shake vigorously for 1 minute. Centrifuge if necessary and use the upper layer.

 ​           Chromatographic system The chromatographic procedure may be carried out using (a) a glass column 2 m long and 2 mm in internal diameter packed with silanized diatomaceous earth for gas chromatography impregnated with 3 per cent w/w of polymethylphenyl siloxane, (b) nitrogen for chromatography as the carrier gas at a flow rate of 30 ml per minute, and (c) a flameionization detector, maintaining the temperature of the column at 120º and that of the injection port and of the detector at 150º.

 ​           Procedure Separately inject 1 μl of Standard solution and Test solution into the chromatograph, record the chromatograms, and measure the areas of the major peaks. The ratio of the response of any dimethylaniline peak to the response of the naphthalene peak obtained from Test solution is not more than that obtained from Standard solution.