Impurity B. Liquid chromatography (2.2.29).

Test solution. Dissolve 0.100 g of the substance to be examined in the mobile phase and dilute to 5.0 mL with the mobile phase.

Reference solution. Dissolve 25.0 mg of sodium azide R (sodium salt of impurity B) in the mobile phase and dilute to 100.0 mL with the mobile phase. Dilute 0.25 mL of this solution to 200.0 mL with the mobile phase.

Column:

— size: l = 0.25 m, Ø = 4 mm;

— stationary phase: strongly basic anion-exchange resin for chromatography R (8.5 µm).

Mobile phase: 4.2 g/L solution of sodium hydroxide R in carbon dioxide-free water R.

Flow rate: 1.0 mL/min.

Detection: conductivity detector with a sensitivity of 3 µS; use a self-regenerating anion suppressor.

Neutralisation of the eluent: either chemical or electrochemical:

— chemical: by continuous countercurrent circulation in a neutralising micromembrane, performed before detection:

— neutralising solvent: 0.025 M sulfuric acid;

— flow rate: 10 mL/min;

— pressure: corresponding to about 100 kPa.

— electrochemical: 300 mA (for example).

Injection: 200 µL.

Run time: 25 min.

Retention time: impurity B = about 14 min.

System suitability: reference solution:

— signal-to-noise ratio: minimum 10 for the peak due to impurity B.

Limit:

— impurity B: not more than the area of the corresponding peak in the chromatogram obtained with the reference solution (10 ppm).