Strategies for inorganic speciation analysis employing spectrometric techniques–Review

Mercury determination in various environmental, food and material complex matrices using unified operating conditions for a cold vapor generation high-resolution continuum source quartz tube atomic absorption spectrometry method

An analytical method with broad applicability based on cold vapor generation high-resolution continuum source quartz tube atomic absorption spectrometry was developed and evaluated for the determination of total mercury in matrices with various complexities and compositions. Sample preparation for different matrices of food, environmental samples and (bio)polymeric materials and unified operating conditions for derivatization and measurement were evaluated. The method was validated according to established requirements (Eurachem Guide 2014, EC Decisions 657/2002; 333/2007; 836/2011 and Association of Official Analytical Chemists Guide - AOAC). Analytical versatility was checked on various samples of fish fillets, mushrooms, soil, water and water sediment, sludge from a wastewater treatment unit, and (bio)polymeric materials from waste recycled from food packaging, computers and garden tools. Under optimal conditions for cold vapor generation in a batch system, namely 3% (v/v) HCl as reaction medium for 5 mL aliquot samples and a volume of 3.5 mL 0.3% (m/v) NaBH4 stabilized in 0.2% (m/v) NaOH as derivatization reagent, the detection limit for Hg in terms of peak height measurement (n = 7 days) was in the range 0.064 ± 0.004 μg L-1 in water, 0.014 ± 0.001 mg kg-1 in environmental samples and 0.009 ± 0.001 mg kg-1 in (bio)polymeric materials. Overall recovery of Hg by analysis of certified reference materials was 102 ± 20% (k = 2) in food, soil, wastewater and water sediment, and polyethylene. Precision for the measurement of various real samples ranged between 4.2 and 15.0%. A performance study highlighted that the method was sensitive, free of non-spectral interference coming from the multielemental matrix and that it complied with the requirements for Hg determination set in EC Decisions and AOAC Guidelines at least for the more common matrices analyzed for social impact.

A novel separation and preconcentration methodology based on direct immersion dual-drop microextraction for speciation of inorganic chromium in environmental water samples

In this study, for the first time, a novel separation and preconcentration method of direct immersion dual-drop microextraction (DIDDME) was proposed for the species of inorganic chromium (Cr(III) and Cr(VI)) followed by graphite furnace atomic absorption spectrometry detection. The methodology is based on that two organic drops hold on the needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent, which can react with a specific species under the same pH value. Therefore, Cr(III) and Cr(VI) can be selectively extracted into different drops. This procedure did not require tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may lead to the risk of sample contamination and analysis errors. Main parameters influencing separation, preconcentration and identification of the target species were investigated. An enrichment factor of 400-fold was obtained for Cr(III) and Cr(VI). Under the optimized conditions, detection limits for this method were 1.1 ng L^-1 and 1.4 ng L^-1 for Cr(III) and Cr(VI) with relative standard deviations of 5.1 and 6.3%, respectively. This procedure was applied for the separation, preconcentration and determination of Cr(III) and Cr(VI) in environmental water samples and certified reference materials with satisfactory results. Recoveries of spiked experiments ranged from 86.0 to 112%.

The importance and status of the micronutrient selenium in South Africa: a review

Selenium (Se) is a vital micronutrient with widespread biological action but leads to toxicity when taken in excessive amounts. The biological benefits of Se are mainly derived from its presence in active sites of selenoproteins such as glutathione peroxidase (GPx). An enzyme whose role is to protect tissues against oxidative stress by catalysing the reduction of peroxidase responsible for various forms of cellular damage. The benefits of Se can be harvested when proper regulations of its intake are used. In South Africa, Se distribution in people's diets and animals are low with socio-economic factors and heterogeneous spread of Se in soil throughout the country playing a significant role. The possible causes of low Se in soils may be influenced by underlying geological material, climatic conditions, and anthropogenic activities. Sedimentary rock formations show higher Se concentrations compared to igneous and metamorphic rock formations. Higher Se concentrations in soils dominates in humid and sub-humid areas of South Africa. Furthermore, atmospheric acid deposition dramatically influences the availability of Se to plants. The studies reviewed in this article have shown that atomic absorption spectroscopy (AAS) is the most utilised analytical technique for total Se concentration determination in environmental samples and there is a lack of speciation data for Se concentrations. Shortcomings in Se studies have been identified, and the future research directions of Se in South Africa have been discussed.

Magnetic dispersive micro-solid phase extraction coupled with dispersive liquid-liquid microextraction followed by graphite furnace atomic absorption spectrometry for quantification of Se(IV) and Se(VI) in food samples

In this work, magnetic dispersive micro-solid phase extraction (MDMSPE) coupled with dispersive liquid-liquid microextraction (DLLME) was developed for Se(IV) and Se(VI) followed by graphite furnace atomic absorption spectrometry. MDMSPE involved the use of magnetic ZnFe₂O₄ nanotubes for adsorbing Se(VI). The sorbent was isolated from aqueous phase by using an external magnetic field instead of tedious centrifugation or filtration. In the following step, Se(IV) in the upper aqueous phase of MDMSPE was enriched by DLLME. Samples were prepared with artificial gastric juice to avoid the inter-conversion of target species. The main factors affecting the determination of the analytes were studied in detail. the detection limits of this method were 1.0 and 1.3 pg mL^-1 for Se(IV) and Se(VI) with relative standard deviations of 4.6% and 5.1% (c = 1.0 ng mL^-1, n = 9), respectively. An enrichment factor of 200 was obtained. This method was used for the detection of Se(IV) and Se(VI) in food samples without any pre-oxidation or pre-reduction operation. A certified reference material of milk powder was analysed by this method, and the determined values were in good agreement with the certified values. Recoveries of spike experiments were in the range of 91.0-107%.