Absolute Quantitation of N-Nitrosamines by Coulometric Mass Spectrometry without Using Standards

CarcinogenicN-nitrosamines were recently found inthe sartan family of drugs and caused many drug recalls. Both oftheir detection and quantification are therefore important. Methodsreported forN-nitrosamine quantitation rely on the use of standardsand are just applicable to simpleN-nitrosamines. There is an urgentneed to quantifyN-nitrosamines derived from drugs with acomplicated structure that lack standards. To tackle the issue, thisstudy describes a novel absolute quantitation strategy forN-nitrosamines using coulometric mass spectrometry (CMS) withoutstandards. In our approach,N-nitrosamine isfirst converted intoelectrochemically active hydrazine via zinc reduction under acidiccondition and the resulting hydrazine can then be easily quantified using CMS. To validate our method, six simpleN-nitrosamines,N-nitrosodiethylamine (NDEA),N-nitroso-4-phenylpiperidine (NPhPIP),N-nitrosodiphenylamine (NDPhA),N-nitrosodibutyl-amine (NDBA),N-nitrosodipropylamine (NDPA), andN-nitrosopiperidine (NPIP), were chosen as test samples, and they all werequantified with excellent measurement accuracy (quantitation error <= 1.1%). Taking this one step further, as a demonstration of themethod utility, a drug-likeN-nitrosamine, (R)-N-(2-(6-chloro-5-methyl-1 '-nitroso-2,3-dihydrospiro[indene-1,4 '-piperidin]-3-yl)propan-2-yl)acetamide (VII), was also synthesized and successfully quantified using our method at 15 ppb level in a complexformulation matrix, following solvent extraction,N-nitrosamine isolation, and reductive conversion. Because of the feature ofrequiring no standards, CMS provides a simple and powerful approach forN-nitrosamine absolute quantitation and has greatpotential for analysis of other drug impurities or metabolites