Redox Speciation of Vanadium in Estuarine Waters Using Improved Methodology Based on Anion Exchange Chromatography Coupled to HR ICP-MS System

Abstract

An improved methodology was developed for V redox speciation in estuarine waters using a hyphenated technique consisting of ion chromatograph (IC) with an anion exchange column and a high-resolution inductively coupled plasma mass spectrometer (HR ICP-MS). This approach enables the direct determination of V(V), whereas reduced species (mainly V(IV)) are calculated by subtracting V(V) concentrations from the measured total V concentration. Based on the “on-column” V(V) chelation mechanism by EDTA, with the eluent composed of 40 mmol L−1 ammonium bicarbonate, 40 mmol L−1 ammonium sulphate, 8 mmol L−1 ethylenediaminetetraacetic acid and 3% acetonitrile, the method was successfully used for analyses of V redox speciation in samples taken in the vertical salinity gradient of the highly stratified Krka River estuary. Due to the matrix effects causing different sensitivities, a standard addition method was used for V(V) quantification purposes. The limit of detection (LOD) was also found to be matrix related: 101.68 ng L−1 in the seawater and 30.56 µg L−1 in the freshwater. Performed stability tests showed that V redox speciation is preserved at least 7 days in un-treated samples, possibly due to the stabilization of V-reduced species with natural organic matter (NOM). The dominant V form in the analysed samples was V(V) with the reduced V(IV) accounting for up to 26% of the total dissolved pool. The concentration of V(IV) was found to correlate negatively with the oxygen concentration. Significant removal of dissolved V was detected in oxygen depleted zones possibly related to the particle scavenging.

Atomic spectrometry update: review of advances in elemental speciation

“…Anion-exchange HPLC was applied to speciation in Amanita muscaria (y agaric mushroom) 174 and in estuarine waters. 175 A. muscaria is unusual in being able to accumulate concentrations of V up to 100 mg kg À1 dw, most of which is present as a compound known as amavadin, whose biological function is not known. In amavadin, V exists in the rather unusual non-oxo V IV ion (the vanadyl ion VO 2+ is more common) and is coordinated by two tetradentate ligands that can coordinate in two distinct orientations, and thus amavadin exists in two isomers.…”

Atomic Spectrometry Update: review of advances in elemental speciation

“…The extraction efficiency was 74 AE 12%, and amavadin, which was found in all parts of all three samples, accounted for 75-96% of the extracted V. All samples also contained several additional, unknown V compounds, including one eluting as late as 52 min. To determine V V in estuarine waters of varying salinity, Knezevic et al 175 optimised an anion-exchange HPLC separation with HR ICP-MS detection with quantication by standard additions. They could not reliably quantify V IV with the method, and so this was determined as the difference between the V V concentration and the total V concentration, which was determined by direct introduction of a sample, diluted 10 times with HNO 3 , into the spectrometer with calibration against standards prepared in 10-times diluted CRM CASS-5 (nearshore seawater) with In as IS.…”

“…Anion-exchange HPLC was applied to speciation in Amanita muscaria (fly agaric mushroom) 174 and in estuarine waters. 175 A. muscaria is unusual in being able to accumulate concentrations of V up to 100 mg kg −1 dw, most of which is present as a compound known as amavadin, whose biological function is not known. In amavadin, V exists in the rather unusual non-oxo V IV ion (the vanadyl ion VO 2+ is more common) and is coordinated by two tetradentate ligands that can coordinate in two distinct orientations, and thus amavadin exists in two isomers.…”