Separation and sweeping of metal ions with EDTA in CZE-ESI-MS

Ethylenediaminetetraacetic acid (EDTA) in the background electrolyte (BGE) of capillary zone electrophoresis coupled to an electrospray ionization mass spectrometer is presented as an approach for the determination of metal ions. Significant signals for the metal-ligand complexes were observed even when EDTA was continually eluted from the capillary during the entire electrophoretic run. The signal-to-noise ratio was improved by the addition of ammonia to the sheath liquid and by using an acquisition m/z range above the m/z of EDTA. The LODs for the test metal ions (i.e. calcium(II), manganese(II), and zinc(II)) with conventional injection were around 1-2 mg/L with corrected peak areas that are linear from 8 to 100 mg/L. The presence of EDTA in the BGE was critical not only for the separation but also for sweeping via complexation as an on-line sample concentration technique. The peak height of the test metal ions was improved at least tenfold with sweeping via EDTA complexation and yielded LODs in the μg/L range.