HPLC/TOF-MS: An alternative to LC/MS/MS for sensitive and selective determination of polar organic contaminants in the aquatic environment

Isobaric interferences in environmental samples can compromise trace LC-MS analysis of polar organic chemicals when using single quadrupole instruments in selected ion monitoring (SIM) mode. HPLC-MS/MS with triple quadrupole instruments in multiple reaction monitoring (MRM) mode is the conventional approach for increasing selectivity and improving sensitivity. Time-of-flight (ToF) MS offers an alternative approach with higher mass resolving power and full spectral sensitivity. Extracts from STP effluent were evaluated for PPCPs using three different types of Micromass, Inc. mass spectrometers: a single quadrupole (LCZ(TM)), a triple quadrupole (Quattro LC(TM)), and an orthogonal acceleration ToF instrument (LCT(TM)). HPLC-ToF-MS provided significant S/N improvement over SIM analysis for each of the analytes detected and approached S/N values afforded by MRM analysis. In addition, the ToF was also able to identify non-target analytes based on accurate mass measurements and associated elemental composition calculation as illustrated by the detection and confirmation of a polyethylene glycol (PEG) homologous series in STP influent. Limited dynamic range on the ToF as compared to the quadrupole was partially corrected for using digital dead time correction (DDTC).