Ultra-high performance liquid chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry for the analysis of benzimidazole compounds in milk samples

• The UHPLC separation of 19 benzimidazoles in a C18 column was optimized.
• The benzimidazoles behavior under atmospheric pressure ionization was studied.
• The mass spectrometry fragmentation (MSn) of these compounds was studied.
• QuEChERS and matrix matched calibration were proposed to analyze milk samples.
• 10 benzimidazoles and 9 metabolites were determined by UHPLC–APCI–MS/MS.

In this work the atmospheric pressure ionization behavior and the tandem mass spectrometry fragmentation of 19 benzimidazoles was studied. Several atmospheric pressure ionization (API) sources (ESI, APCI and APPI) were evaluated showing that APCI was the best option, mainly for KETO-TCB that provided a 20 times improvement versus ESI. From the studies of tandem mass spectrometry, fragmentation pathways were proposed thus characterizing the most abundant and interesting product ions and selecting the most abundant and selective ones for the confirmatory quantitative method performed in SRM mode in a triple quadrupole mass analyzer. For quantitative analysis, the 19 benzimidazoles were separated in less than 7 min using a C18 column packed with superficially porous particles providing high efficiency within the range of UHPLC. A QuEChERS-like sample treatment was applied to milk samples before the UHPLC–APCI–MS/MS determination providing method limits of quantitation that ranged from 0.6 to 3 μg kg−1 and showing good repeatability (RSD: 2–18%) and accuracy (relative errors: 1–23%) suitable for using this method for routine analysis.