Enhancing LC-MS method sensitivity for the quantification of 5-nitroimidazoles in animal liver using high-field asymmetric waveform ion mobility spectrometry (FAIMS)

To help protect the Canadian food supply, liquid chromatography-mass spectrometry (LC-MS) methods are used by the Canadian Food Inspection Agency (CFIA) to quantify veterinary drug residues in tissues of food animals. Some veterinary drugs are banned for use in food producing animals in Canada because of adverse health risks for humans, and for these drugs, the desire is to create the most sensitive methods possible. The use of 5-nitroimidazoles in food animals is banned in Canada and other jurisdictions because of their toxic adverse effects. Currently, the CFIA does not have a method for 5-nitroimidazoles in animal liver and a highly sensitive method is desired. The development of a method for 5-nitroimidazoles in animal liver is reported for nine 5-nitroimidazoles using LC-multiple reaction monitoring (MRM) on a triple quadrupole MS, with and without high-field asymmetric waveform ion mobility spectrometry (FAIMS). With LC-MRM, the chemical background was problematic for four analytes in particular, resulting in higher limit of quantification (LOQ) and limit of detection (LOD) values compared with LC-FAIMS-MRM. With FAIMS, all nine 5-nitroimidazoles could be detected at an LOQ of 0.125 ng/g and 6 had an LOD of 0.031 ng/g. Furthermore, since FAIMS filters the majority of chemical background in the gas-phase, LC-FAIMS-MRM is more tolerant to changes in the liver matrix resulting in a more robust analysis. In particular, changes in the liver matrix affected LOQ values using LC-MRM for five of the analytes, whereas the LOQ values were unaffected using LC-FAIMS-MRM.