Development and validation of a rapid method for the determination and confirmation of 10 nitroimidazoles in animal plasma using liquid chromatography tandem mass spectrometry

A rapid LC-MS/MS method has been developed and validated for the simultaneous identification, confirmation and quantitation of 10 nitroimidazoles in plasma. The method validated in accordance with Commission Decision (CD) 2002/657/EC is capable of analysing for metronidazole (MNZ), dimetridazole (DMZ), ronidazole (RNZ), ipronidazole (IPZ) and their hydroxy metabolites MNZ-OH, HMMNI (hydroxymethyl, methyl nitroimidazole), IPZ-OH. The method is also capable of analysing carnidazole (CRZ), ornidazole (ORZ) and ternidazole (TRZ) which are rarely analysed by modern methods. MNZ, DMZ and RNZ have a recommended level (RL) of 3 ng mL^-1 which this method is easily able to detect for all the nitroimidazole compounds. Plasma samples are extracted with acetonitrile, and NaCl is added to help remove matrix contaminants. The acetonitrile extract undergoes a liquid-liquid wash step with hexane; it is then evaporated and reconstituted in mobile phase. The reconstituted samples are analysed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The decision limits (CCα) range from 0.5 to 1.6 ng mL^-1 and the detection capabilities (CCβ), range from 0.8 to 2.6 ng mL^-1. The results of the inter-assay study, which was performed by fortifying bovine plasma samples (n = 18) on three separate days, show the accuracy calculated for the various analytes range between 101% and 108%. The precision of the method, expressed as CV% values for the inter-assay variation of each analyte at the three levels of fortification (3, 4.5 and 6.0 ng mL^-1), ranged between 4.9% and 15.2%. A day 4 analysis was carried out to examine species variances in animals such as avian, ovine, porcine and equine.