Analysis of anionic metallized azo and formazan dyes by capillary electrophoresis-mass spectrometry

Capillary electrophoresis-mass spectrometry was applied to the separation o f several anionic dyes containing copper(II), chromium(III), or cobalt(III) as part of the dye molecule. The dyes were separated using a 110 cmX50 mu m uncoated fused-silica capillary and a 5 mM ammonium acetate buffer (pH 9) containing 40% acetonitrile. Excellent separation efficiencies (N = 500 00 0 plates/column) and low detection limits of 20-50 pg (selected ion monitor ing, S/N = 10) were achieved. Mass spectra were acquired at different cone voltages. At low cone voltages (low collision energies), sensitivity was ma ximized and the mass spectra contained only signals of the (multiply charge d) molecular ions and low levels of sodium ion and proton adducts. At highe r cone voltages, the 2:1 (ligand:metal) chromium and cobalt dyes showed los ses of one of the two dye ligands, accompanied by a reduction of the metal. The copper dyes showed signals due to loss of SO2 and SO3- but no release of metal. Azo cleavage, otherwise typical of azo dyes, was not observed wit h the metallized dyes. (C) 2000 Elsevier Science B.V. All rights reserved.