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 liquid chromatography-electrospray ionization (ESI) mass spectrometry. In this study trifluoroacetic acid, heptafluorobutanoic acid and perfluoroheptanoic acid were used as ion-pairing reagents. The signal intensities of eight amine analytes were measured in the presence of these fluorinated carboxylic 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 carboxylic acids were added to the mobile phase at useful concentrations. The use of these acids in ion-pair chromatography was also compared to the more conventional sodium heptane sulphonate additive. It was found that the chromatographic performance was comparable. Finally, the long-term performance of the ESI interface and the chemical background caused by these fluorinated reagents were examined. No degradation of the ESI interface performance could be seen for over 24 h of continuous infusion.