Rapid analysis of trace organic compounds in water by automated online solid-phase extraction coupled to liquid chromatography-tandem mass spectrometry

A fully automated online solid-phase extraction (SPE) with directly coupled liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for analysis of 34 trace organic compounds in diverse water matrices has been developed. The current method offers several advantages over traditional offline SPE methods including low sample volume (1.7 mL), decreased solvent use, higher throughput, and increased reproducibility. The method uses simultaneous positive and negative ESI for analysis of all compounds in one injection, which reduces cycle time (extraction+analysis) to <15 min. Method optimization included testing different online SPE cartridges, mobile phase compositions, and flow rates. The method detection limits (MDLs) ranged from 0.1 to 13.1 ng/L with 80% of the compounds having an MDL <5 ng/L. Matrix spike recoveries in three different water qualities were evaluated and ranged from 61.2% to145.1% with 95% of the recoveries ranging between 70-130%. As part of the method validation studies, linearity (0.9911-0.9998), intra-day variability (1.0-10.4%), inter-day variability (1.0-11.9%), and matrix effects were also assessed. The use of 26 isotopically-labeled standards increased the reliability of the method while retention time locking and use of two transitions for most compounds increased the specificity. The applicability of the method was tested on samples across treatment points from two wastewater plants, a septic tank, surface water and groundwater.