Appendix VIII N. N,N-Dimethylaniline

(Ph. Eur. method 2.4.26)

METHOD a

Examine by gas chromatography (2.2.28), using N,N-diethylaniline R as the internal standard.

Internal standard solution Dissolve 50 mg of N,N-diethylaniline R in 4 mL of 0.1 M hydrochloric acid and dilute to 50 mL with water R. Dilute 1 mL of this solution to 100 mL with water R.

Test solution Dissolve in a ground-glass-stoppered tube 0.50 g of the substance to be examined in 30.0 mL of water R. Add 1.0 mL of the internal standard solution. Adjust the solution to a temperature of 26-28 °C. Add 1.0 mL of strong sodium hydroxide solution R and mix until completely dissolved. Add 2.0 mL of trimethylpentane R. Shake for 2 min and allow the phases to separate. Use the upper layer.

Reference solution Dissolve 50.0 mg of N,N-dimethylaniline R in 4.0 mL of 0.1 M hydrochloric acid and dilute to 50.0 mL with water R. Dilute 1.0 mL of this solution to 100.0 mL with water R. Dilute 1.0 mL of this solution to 30.0 mL with water R. Add 1.0 mL of the internal standard solution and 1.0 mL of strong sodium hydroxide solution R. Add 2.0 mL of trimethylpentane R. Shake for 2 min and allow the phases to separate. Use the upper layer.

The chromatographic procedure may be carried out using:

— a fused-silica capillary column 25 m long and 0.32 mm in internal diameter coated with cross-linked polymethylphenylsiloxane R (film thickness 0.52 µm),
— helium for chromatography R as the carrier gas with a split ratio 1:20, a column head pressure of 50 kPa and a split vent of 20 mL/min,
— a flame-ionisation detector,
— a split-liner consisting of a column about 1 cm long packed with diatomaceous earth for gas chromatography R impregnated with 10 per cent m/m of poly(dimethyl)siloxane R,

maintaining the temperature of the column at 150 °C for 5 min, then raising the temperature at a rate of 20 °C per min to 275 °C and maintaining it at 275 °C for 3 min and maintaining the temperature of the detector at 300 °C and that of the injection port at 220 °C.

The retention times are: N,N-dimethylaniline about 3.6 min, N,N-diethylaniline about 5.0 min.

Inject 1 µL of the test solution and 1 µL of the reference solution.

mETHOD b

Examined by gas chromatography (2.2.28), using naphthalene R as the internal standard.

Internal standard solution Dissolve 50 mg of naphthalene R in cyclohexane R and dilute to 50 mL with the same solvent. Dilute 5 mL of this solution to 100 mL with cyclohexane R.

Test solution To 1.00 g of the substance to be examined 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 min. Centrifuge if necessary and use the upper layer.

Reference solution To 50.0 mg of N,N-dimethylaniline R add 2 mL of hydrochloric acid R and 20 mL of water R, shake to dissolve and dilute to 50.0 mL with water R. Dilute 5.0 mL of this solution to 250.0 mL with water R. 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 min. Centrifuge if necessary and use the upper layer.

The chromatographic procedure may be carried out using:

— a glass column 2 m long and 2 mm in internal diameter packed with silanised diatomaceous earth for gas chromatography R impregnated with 3 per cent m/m of polymethylphenylsiloxane R,
— nitrogen for chromatography R as the carrier gas at a flow rate of 30 mL/min,
— a flame-ionisation detector,

maintaining the temperature of the column at 120 °C and that of the injection port and of the detector at 150 °C.

Inject 1 µL of the test solution and 1 µL of the reference solution.