Reversed-phase ion-pair chromatography coupled to electrospray ionisation mass spectrometry by on-line removal of the counter-ions

A strong anion-exchanger was used as a trapping column to perform on-line c oupling of ion-pair chromatography with electrospray ionisation mass spectr ometry. Ion-pairing reagents were used to retain polar analytes of low mole cular mass away from the solvent front in reversed-phase LC. The trapping c olumn enabled removal of the non-volatile counter-ions from the mobile phas e prior to detection, so that the electrospray process could be performed w ith favourable ionisation conditions and without contamination of the inter face. The efficiency of the trapping process was studied for 1-octanesulfon ic acid and sodium dodecyl sulfate as ion-pairing reagents. Using this on-l ine trapping method, biopterin and guanidine could be retained with a k'>2 and detected by electrospray mass spectrometry with a stable signal. (C) 19 99 Elsevier Science B.V. All rights reserved.