Analysis of perchlorate in groundwater by electrospray ionization mass spectrometry/mass spectrometry

An electrospray ionization mass spectrometry/mass spectrometry (ESI/MS/MS) method was developed to measure part-per-billion (μg/L) concentrations of perchlorate in groundwater. Selective and sensitive perchlorate detection was achieved by operating the mass spectrometer in the negative ionization mode and by using MS/MS to monitor the ClO₄^- to ClO₃^- transition. The method of standard additions was used to address the considerable signal suppression caused by anions that are typically present in groundwater, such as bicarbonate and sulfate. ESI/MS/MS analysis was rapid, accurate, reproducible, and provided a detection limit of 0.5 μg/L perchlorate in groundwater. Accuracy and precision of the ESI/MS/MS method were assessed by analyzing performance evaluation samples in a groundwater matrix (4.5-75 μg/L perchlorate) and by comparing ion chromatography (IC) and ESI/MS/MS results for local groundwater samples (<0.5-35 μg/L perchlorate). Results for the performance evaluation samples differed from the certified values by 4-13%, and precision ranged from 3 to 10% (relative standard deviation). The IC and ESI/MS/MS results were statistically indistinguishable (P > 0.05) for perchlorate concentrations above the detection limits of both methods.