A versatile electrophoric derivatisation reagent for negative ion chemical ionisation mass spectrometry: o-(pentafluorobenzyloxycarbonyl)-2,3,4,5-tetrafluorobenzoyl chloride

Abstract

The synthesis of a novel electrophoric derivatisation reagent, o-(pentafluorobenzyloxycarbonyl)-2,3,4,5-tetrafluorobenzoyl chloride, is described. The reagent was tested against selected primary and secondary amino compounds, as well as phenolic and aliphatic hydroxyl compounds as analytical targets. The derivatives exhibit excellent mass spectral properties under negative ion chemical ionisation, i.e. reduced fragmentation and thus high ion current for the targeted m/z during analysis. Since the reagent bears a pentafluorobenzyl ester group, resulting negative ion chemical ionisation mass spectra were expectedly dominated by dissociative resonance electron capture typically observed with these compounds, additionally showing neutral loss of carbon dioxide and ammonia (in the case of primary amines). The reagent is suitable for detecting the target compounds with high sensitivity, as exemplified for the analysis of amphetamine and methylphenidate from human plasma where chromatographic background is drastically reduced by a shift in detected m/z and retention time and lower limits of quantification at 7.8 pg/mL (amphetamine) and 4.5 pg/mL (methylphenidate) can be obtained. The choice of two or three target quantification masses allows selective detection and adjustment of lowest background interference. No carryover effect was observed for the derivatives of amphetamine and methylphenidate.