Direct nano-electrospray ionization tandem mass spectrometry for quantification and identification of metronidazole in its dosage form and human urine

A rapid, sensitive, and direct nano-electrospray ionization-tandem mass spectrometry (NS-ESI-MS/MS) method using an off-line nanospray (NS) capillary has been developed and validated for the analysis of metronidazole (MTZ). A mixture of 2µL MTZ sample solution prepared in an ionization solvent consisting of methanol: water: formic acid in a ratio of 80:20:0.3, together with 2µL of an internal standard (IS), 1,3,6-polytyrosine, is loaded into the back of the NS capillary. The NS capillary was fitted into the ion source at a distance of 3 mm between the NS tip and MS orifice. Sample is then analyzed and acquired sustainable signal that allowed for data compilation across various data points for MTZ identification and quantification. The quantification relied on the ratio of the [M+H]+ peaks of MTZ and IS with m/z values of 172.0717 and 182.0812, respectively, while the identification relied on the MS/MS of the precursor ions [M+H]+ of both compounds and their fragments at 128.05 for MTZ and 165.1 and 136.07 for the IS. The NS-ESI-MS/MS method was accurate and precise for the quantification of MTZ over concentration range from 2.5 to 25000 ng/mL. The applicability of the method was confirmed by MTZ analysis in its pharmaceutical dosage form as well as detection of the analyte in clinical human urine samples without any sample treatment procedure.
Methods
Data files were generated as XCalibur raw data files (.raw), and can be read using the ThermoScientific XCalibur system. Results were extracted manually from these files as described in the published method.