Analytica Chimica Acta 585 (2007) 32–37 Confirmation of vanadium complex formation using electrospray mass spectrometry and determination of vanadium speciation by sample stacking capillary electrophoresis ZuLiang Chen a,∗ , Gary Owens a , Ravendra Naidu a,b a Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia b CRC for Contamination Assessment and Remediation of Environments, Mawson Lakes Boulevard, Mawson Lakes, SA 5095, Australia Received 8 September 2006; received in revised form 6 December 2006; accepted 7 December 2006 Available online 10 December 2006 Abstract Capillary zone electrophoresis (CZE) with UV detection was used to determine vanadium species. Nitrilotriacetic acid (NTA), hydrox- yethylethylenediaminetriacetic acid (HEDTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylene glycol-bis(2-aminoethylether)-tetraacetic acid (EGTA) and 2,6-pyridinedicarboxylic acid (PDCA) were investigated to determine whether these ligands formed stable anionic complexes with vanadium. Of all the ligands studied HEDTA was the most suitable ligand because it gave the largest UV response with reasonable migration time. Electrospray mass spectrometry (ES-MS) was used to confirm the formation of [VO 2 (HEDTA)] 2- and [VO(HEDTA)] 1- in solution. An electrolyte containing 25 mM phosphate, 0.25 mM tetradecyltrimethylammonium bromide (TTAB) at pH 5.5 was optimum for the separation of these anionic vanadium complexes. Sample stacking techniques, including large-volume sample stacking (LVSS) and field-amplified sample injection (FASI), were tested to improve the sensitivity. Best sensitivity was obtained using FASI, with detection limits of 0.001 M, equivalent to 0.4 gL -1 , for [VO 2 (HEDTA)] 2- and 0.01 M, equivalent to 3.4 gL -1 for [VO(HEDTA)] 1- . The utility of the method for the speciation of V(IV) and V(V) was demonstrated using ground water samples. © 2006 Elsevier B.V. All rights reserved. Keywords: Capillary zone electrophoresis; Vanadium speciation; Electrospray mass spectrometry; Sample stacking techniques 1. Introduction It has long been recognized that the determination of only total vanadium concentrations is insufficient for many environ- mental considerations as the toxicity of vanadium depends on the chemical species present [1]. Hence, techniques capable of accurate and efficient vanadium speciation in environmen- tal samples are important for environmental risk assessment. A number of analytical techniques can be used for vanadium speciation. Ion chromatography (IC) with various detection techniques are frequently used for the simultaneous determi- nation of vanadium species. However, since the concentration of vanadium in environmental samples is commonly towards the lower levels, vanadium speciation usually requires powerful detection techniques such as atomic absorption spectrometry ∗ Corresponding author. Tel.: +61 8 83025057; fax: +61 83023057. E-mail address: zuliang.chen@unisa.edu.au (Z. Chen). (AAS) [2,3], inductively coupled plasma mass spectrometry (ICP-MS) [4–7], inductively coupled plasma optical emission spectrometry (ICP-OES) [8], or visible spectrophotometry with post-column derivatization [9]. These methods are all useful and offer high detection sensitivity for vanadium species in real samples. However, they still do not satisfy all requirements for routine analysis because of the need for expensive instruments such as ICP-OES and ICP-MS or for a time consuming derivi- tisation step. What is required is a less capital-intensive rapid technique capable of vanadium speciation in environmental sam- ples with high sensitivity. Capillary zone electrophoresis (CZE) is an attractive approach for the separation of metal species [10] due to its high separation efficiency and speed. In principle, two approaches are typically used for the separation of metals using (1) on-capillary complexation and (2) pre-capillary complexation. During on- capillary complexation, soluble weakly complexing ligands, usually carboxylic acids, are added to the running electrolyte and weak complexes are rapidly formed online and detected using 0003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2006.12.008