Determination of ethylenediaminetetraacetic acid as the nickel chelate in environmental water by solid‐phase extraction and capillary electrophoresis/tandem mass spectrometry

An automated extraction procedure using solid-phase extraction (SPE) disk technology was developed for the qualitative and quantitative determination of ethylenediaminetetraacetic acid (EDTA) in water samples. The procedure involves conversion of all free and chelated EDTA present into the nickel EDTA chelate followed by extraction on strong anion exchange extraction disks. A 5 mL water sample is extracted and concentrated to 30 μL. This extract is then analyzed by capillary electrophoresis (CE) using ion spraytandem mass spectrometry (MS) for selective detection. An amine-coated capillary column is used to separate anions using negative voltage and high electroosmotic flow. A self-aligning liquid junction is used as the CE/MS interface. The sample is injected using field amplification for enhanced concentration detection limits down to 0.15 μg/L. This detection limit is about five times lower than any report we have found in the literature and provides the unique specificity afforded by mass spectrometry. Total sample preparation and run time was forty minutes per sample, including evaporation steps and capillary rinsing between runs. A tray of 24 vials, including samples and standards, was analyzed for these experiments and was easily finished within one day. These experiments demonstrate that CE/MS can be a rugged, quantitative technique, which, with proper sample preparation and focusing techniques, can compete with the concentration sensitivity of established analytical methods.