Negative ion electrospray of bromo- and chloroacetic acids and an evaluation of exact mass measurements with a bench-top time-of-flight mass spectrometer

The negative ion electrospray mass spectra of six bromo- and chloroacetic a cids were measured using two different electrospray interfaces and single q uadrupole and bench-top time-of-flight mass spectrometers. With each acid a t 50 mu g/mL in aqueous methanol at pH 10, the anions observed included dep rotonated molecules, adducts, and fragment ions. With each acid at 100 ng/m L in aqueous acetonitrile at pH 10, mainly deprotonated molecules are obser ved. The exact m/z measuring capability of the time-of-flight mass spectrom eter was evaluated to assess the potential for the determination of the ind ividual acids in mixtures without an on-line separation Mean measurement er rors were nearly always less than +/- 9 ppm and the majority were less than +/- 5 ppm. Potential interferences by substances having similar exact: mas ses and the ability to form anions in aqueous solutions were evaluated. The estimated detection limits of the five regulated haloacetic acids in drink ing water, without a sample preconcentration step, are in the range of 24-8 6 ng/mL, which is within about a factor of 10 of the levels required for ro utine monitoring of the acids. Actual drinking water samples were not. anal yzed pending the development of slightly more sensitive techniques and quan titative analytical procedures. (C) 2000 American Society for Mass Spectrom etry.