Simultaneous and trace level quantification of two potential genotoxic impurities in valsartan drug substance using UPLC-MS/MS.

A sensitive and selective Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) method was developed for the identification and quantification of two potential genotoxic impurities (PGIs) - viz. methyl N-((2'-(1H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl)methyl)-N-nitroso-L-valinate (PGI-1) and N-nitroso Valsartan (PGI-2) - in the angiotensin II receptor blocker valsartan. Among these impurities, PGI-1 is a distinctive compound which has never been reported. For this, chromatographic separation was performed using a Waters XBridge BEH C18 column (150 mm × 4.6 mm, 2.5 µm), with ammonium acetate aqueous solution (0.01 mol/L) as mobile phase A and acetonitrile as mobile phase B, in a gradient elution mode at a 0.5 mL/min flow rate. Mass spectrometric conditions were optimized using electrospray ionization (ESI) in positive mode. Following the International Conference of Harmonization (ICH) guidelines, this methodology is capable of quantifying 2 PGIs at 0.016 ppm in samples at 50 mg/mL concentration. This validated approach presented good linearity over the concentration range of 0.016-0.06 ppm for 2 PGIs. The correlation coefficient of each impurity was observed greater than 0.999. The accuracy of this method was in the range of 83-113% for the aforementioned PGIs. In addition, expert knowledge rules (Derek-based) and statistical (Q) SAR evaluation system (Sarah-based) were used to evaluate and classify the genotoxicity of both valsartan-related PGIs as well as to define their standard limits. The predicted results were positive and classified into the third category, and the total nitrosamine limit was set to 0.03 ppm. As such, this approach represents a good quality control system for the simultaneous and precise quantitation of PGIs in valsartan.