On-line separation/preconcentration of V(IV)/V(V) in environmental water samples with CTAB-modified alkyl silica microcolumn and their determination by inductively coupled plasma-optical emission spectrometry

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

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.

A global systematic review, meta-analysis, and risk assessment of the concentration of vanadium in drinking water resources

The presence of toxic metals such as vanadium in water resources has attracted considerable attention as a new concern in international health. Systematic review and meta-analysis were performed to assess the concentration of vanadium in water resources along with the relevant ecological risk assessment. Databases of Scopus, PubMed, and Embase were investigated to retrieve the related articles from January 01, 1974 to December 25, 2019. Twenty-eight articles containing 152 samples from 24 countries were included. Furthermore, the meta-analysis was conducted by the approach of z-score to estimate differences in the effect size. In addition, the mean of concentrations of vanadium was applied to calculate the risk assessment only to the water surface and choose the maximum environmental concentration (MEC) for demonstrate a worst-case scenario. Here, the risk assessment approach was used to show that the MEC of vanadium confirm the risk it for aquatic ecosystems, being fish (e.g., Danio rerio) our model organism due to their sensibility. According to findings, the MEC of vanadium in surface water varied from 0.010 μg L^-1 (USA) and 68 μg L^-1 (China), with an overall mean of 6.21 ± 13.3 μg L^-1 (mean ± standard deviation). The ecological risk assessment demonstrated that people living in some countries such as China and Japan were at an adverse ecological risk of vanadium in the water resources. Hence, essential control plans besides adequate removal techniques must be implemented for significant deracination of heavy metals like vanadium.

Miniaturized and direct spectrophotometric multi-sample analysis of trace metals in natural waters

Trends in the analysis of trace metals in natural waters are mainly based on the development of sample treatment methods to isolate and pre-concentrate the metal from the matrix in a simpler extract for further instrumental analysis. However, direct analysis is often possible using more accessible techniques such as spectrophotometry. In this case a proper ligand is required to form a complex that absorbs radiation in the ultraviolet-visible (UV-Vis) spectrum. In this sense, the hydrazone derivative, di-2-pyridylketone benzoylhydrazone (dPKBH), forms complexes with copper (Cu) and vanadium (V) that absorb light at 370 and 395 nm, respectively. Although spectrophotometric methods are considered as time- and reagent-consuming, this work focused on its miniaturization by reducing the volume of sample as well as time and cost of analysis. In both methods, a micro-amount of sample is placed into a microplate reader with a capacity for 96 samples, which can be analyzed in times ranging from 5 to 10 min. The proposed methods have been optimized using a Box-Behnken design of experiments. For Cu determination, concentration of phosphate buffer solution at pH 8.33, masking agents (ammonium fluoride and sodium citrate), and dPKBH were optimized. For V analysis, sample (pH 4.5) was obtained using acetic acid/sodium acetate buffer, and masking agents were ammonium fluoride and 1,2-cyclohexanediaminetetraacetic acid. Under optimal conditions, both methods were applied to the analysis of certified reference materials TMDA-62 (lake water), LGC-6016 (estuarine water), and LGC-6019 (river water). In all cases, results proved the accuracy of the method.