Separation of o-, m- and p-phthalic acids by high-field asymmetric waveform ion mobility spectrometry (FAIMS) using mixed carrier gases

Baseline separation of the three isomers of phthalic acid was achieved in a mixed gas system containing a 95:5 mixture of N-2 and CO2, even though the acids could not be distinguished by high-held asymmetric waveform ion mobi lity spectrometry (FAIMS) when either pure N-2 or pure CO2 was used as the carrier gas, Pseudomolecular anions of o-, m- and p-phthalic acids were gen erated by electrospray ionization and detected, following separation by FAI MS, using a quadrupole mass spectrometer, Addition of small amounts of CO2 to an N-2 carrier gas also caused the compensation voltages to increase by as much as 12 V, accompanied by 2-7-fold improvements in the measured ion c urrent and dramatic reductions in both adduct ion formation and parent ion fragmentation. Copyright (C) 2000 John Wiley & Sons, Ltd.