Speciation of V, Cr and Fe by capillary electrophoresis–bandpass reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis–dynamic reaction cell inductively coupled plasma mass spectrometry (CE–DRC-ICP-MS) for the speciation of iron(III/II), vanadium(V/IV) and chromium(VI/III) is described. Two different CE migration modes were employed for separating the six metal ions using pre-capillary complexation. One is counter-electroosmotic mode in which iron(III/II) and vanadium(V/IV) ions were well separated using a 60 cm×75 μm i.d. fused silica capillary. The voltage was set at +22 kV and a 15 mmol l−1 tris(hydroxymethyl)aminomethane (Tris) buffer (pH 8.75) containing 0.5 mmol l−1 ethylenediaminetetraacetic acid (EDTA) and 0.5 mmol l−1 ortho-phenanthroline (phen) was used as the electrophoretic buffer. The other is co-electroosmotic mode in which chromium(VI/III) ions were well separated while the applied voltage was set at −22 kV and a 10 mmol l−1 ammonium citrate buffer (pH 7.7) containing 0.5 mmol l−1 diethylenetriaminepentaacetic acid (DTPA) and 0.01% polybrene was used as the electrophoretic buffer. The mass spectra were measured at m/z 51, 52 and 56 for V, Cr and Fe, respectively. The interfering polyatomic ions of 35Cl16O+, 40Ar12C+ and 40Ar16O+ on 51V+, 52Cr+ and 56Fe+ determination were reduced in intensity significantly by using NH3 as the reaction cell gas in the DRC. The detection limits were in the range of 0.1–0.5, 0.4–1.3 and 1.2–1.7 ng ml−1 for V, Cr and Fe, respectively. Applications of the method for the speciation of V, Cr and Fe in wastewater were demonstrated. The recoveries were in the range of 92–120% for various species.