Determination of Sodium Azide and Tetrabutylammonium Bromide Residues in Active Pharmaceutical Ingredients of Candesartan Cilexetil by Ion Chromatography with Solid Phase Extraction

Candesartan cilexetil (about 100 mg) was extracted ultrasonically with water for 15 min and centrifuged for 10 min. The supernatant was passed through 0.22 μm filter membrane, and the collected filtrate was passed through pre-activated C₁₈ solid phase extraction cartridge. The eluent was flowed into the ion chromatograph and separated on IonPac AS18 anion exchange chromatographic column at 35℃ of the column temperature. The programmed rinse was performed with potassium hydroxide solution, and the conductmetric detector was used for detection. As shown by the results, the resolutions of N₃^--NO₃^- and Br^--NO₃^- in water were both greater than 1.50, and the interference of other impurity ions in active pharmaceutical ingredients(API) and solvent water was smaller. Linear relationships between values of peak area and mass concentration of N₃^- and Br^- were found in definite ranges, with detection limits (3S/N) of 0.000 70 mg·L^-1 for N₃^- and 0.001 4 mg·L^-1 for Br^-, respectively. Test for recovery was made on the blank sample at 3 concentration levels by standard addition method, giving results in the range of 88.2%-93.5% and 101%-104%, respectively, with RSDs (n=6) of the determined values of 2.6% and 0.55%, respectively. The method was applied to the analysis of actual samples, and satisfactory results were obtained.