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

Abstract

A rapid, sensitive and direct nano-electrospray ionization-tandem mass spectrometry (NS-ESI-MS/MS) method, using an offline nanospray (NS) capillary, has been developed and validated for the analysis of metronidazole (MTZ). A mixture of 2 µl MTZ sample solution prepared in an ionization solvent consisting of methanol : water : formic acid in a ratio of 80 : 20 : 0.3, together with 2 µl 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. The sample is then analysed and acquired a 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 the concentration range from 2.5 to 25 000 ng ml ⁻¹. The applicability of the method was confirmed by MTZ analysis in its pharmaceutical dosage form and detection of the analyte in clinical human urine samples without any sample treatment procedure.