Studies of signal suppression in liquid chromatography-electrospray ionization mass spectrometry using volatile ion-pairing reagents

Volatile ion-pairing reagents are useful due to their compatibility with li quid chromatography-electrospray ionization (ESI) mass spectrometry. In thi s study trifluoroacetic acid, heptafluorobutanoic acid and perfluoroheptano ic acid were used as ion-pairing reagents. The signal intensities of eight amine analytes were measured in the presence of these fluorinated carboxyli c acids and compared with the signal intensity when using an ion-pair free formic acid-ammonium formate buffer. It was shown that the ESI signal from most of the studied analytes decreased about 30-80% when the fluorinated ca rboxylic, acids were added to the mobile phase at useful concentrations. Th e use of these acids in ion-pair chromatography was also compared to the mo re conventional sodium heptane sulphonate additive. It was found that the c hromatographic performance was comparable. Finally, the long-term performan ce of the ESI interface and the chemical background caused by these fluorin ated reagents were examined. No degradation of the ESI interface performanc e could be seen for over 24 h of continuous infusion. (C) 2001 Published by Elsevier Science B.V.