The successful coupling of a thin-layer, flow-by electrochemical cell on-line with electrospray mass spectrometry (ES-MS) for electrochemically modulated sample preconcentration and clean up, using copper(II) as the targeted analyte, is demonstrated. Particular requirements for the interfacing of this electrochemical system with ES-MS, the choice of cell and electrode materials, and the solvent and electrolyte requirements are addressed. The transfer of Cu2+ at low μg/L levels from matrices that cannot be analyzed directly by ES-MS, including 100% aqueous solutions containing up to 1% (v/v) HNO3 and 1% (w/w) NaCl, to a more suitable medium (i.e. CH3OH/H2O (95/5 v/v) with 5.0 mM ammonium acetate and 0.75% (v/v) acetic acid) via electrochemically controlled reduction (deposition) and oxidation (stripping) of the Cu2+ is demonstrated. Acidic samples and samples containing significant levels of dissolved solids required cell washout times of up to 4.0 min following electrochemical extraction. Nonetheless, analysis time was still less than 8 min per sample. Quantification of 20–50 μg/L Cu2+ in various matrices using standard additions with this electrochemical/ES-MS combination is evaluated. The limitations of this combination in its present state of development and possible future directions are summarized.
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Pretty et al. (1998) studied this question.