Method for determination of elemental impurities in metronidazole benzoate using inductively coupled plasma mass spectrometry

Rationale: Metronidazole benzoate is widely used to treat a variety of infections. The presence of elemental impurities in drug products harms the normal physiological system without any therapeutic effects. To ensure the quality and safety of benzoyl metronidazole, a method for the simultaneous determination of 7 elemental impurities in metronidazole benzoate needs to be established. Methods: Ge was used as the internal standard element to compensate for matrix effects. The samples were processed by direct dissolution and measured by inductively coupled plasma mass spectrometry in kinetic energy discrimination(KED) mode. The method was validated by USP Pharmacopoeia chapter <233> Elemental Impurities-Procedure. Results: The correlation coefficients of the standard curves of 7 elemental impurities were not less than 0.999. The limits of detection were in the range of 0.0010~0.0487 μg/g and the limits of quantification were in the range of 0.0280 ~ 0.0306 μg/g. The recoveries were within the range of 76.5%~119.4% and the precision RSD(%) was 0.39%~1.59%(n=6). The contents of 7 elemental impurities in the three batches of metronidazole benzoate were originally below their limits and less than 30% of the control threshold, in accordance with the ICH Q3D guidelines. Conclusion: This newly developed and validated inductively coupled plasma mass spectrometric method for estimating elemental impurities(As, Cd, Hg, Pb, V, Vo, and Ni) in metronidazole benzoate was within the permitted limit and suitable for routine use.