UV Irradiation Controlled Cold Vapor Generation Using SnCl2 as Reductant for Mercury Speciation

Mobility, spatial variation and human health risk assessment of mercury in soil from an informal e-waste recycling site, Lagos, Nigeria

Spatial variations and mobility of mercury (Hg) and Hg associations with other potentially toxic elements (PTEs) were studied in soil samples from Alaba, the largest e-waste recycling site in Nigeria and West Africa. Total Hg concentration was determined in surface soil samples from various locations using cold vapour atomic absorption spectrometry (CVAAS) following microwave-assisted acid extraction, while sequential extraction was used to determine operationally defined mobility. The concentrations of the PTEs arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn) metals were determined using inductively coupled plasma mass spectrometry (ICP-MS) following microwave-assisted digestion with aqua regia. Total Hg concentration ranged from < 0.07 to 624 mg/kg and was largely dependent on the nature and intensity of e-waste recycling activities carried out. Mobile forms of Hg, which may be HgO (a known component of some forms of e-waste), accounted for between 3.2 and 23% of the total Hg concentration, and were observed to decrease with increasing organic matter (OM). Non-mobile forms accounted for >74% of the total Hg content. In the main recycling area, soil concentrations of Cd, Cd, Cu, Hg, Mn, Ni, Pb and Zn were above soil guideline values (Environment Agency in Science Report, 2009; Kamunda et al., 2016). Strong associations were observed between Hg and other PTEs (except for Fe and Zn) with the correlational coefficient ranging from 0.731 with Cr to 0.990 with As in April, but these correlations decreased in June except for Fe. Hazard quotient values > 1 at two locations suggest that Hg may pose health threats to people working at the e-waste recycling site. It is therefore recommended that workers should be investigated for symptoms of Hg exposure.

Single-Drop Solution Electrode Discharge-Induced Cold Vapor Generation Coupling to Matrix Solid-Phase Dispersion: A Robust Approach for Sensitive Quantification of Total Mercury Distribution in Fish

Sensitive quantification of mercury distribution in fish is challenging because of insufficient sensitivities of conventional analytical methods, the limited mass of organs (tens of micrograms to several milligrams), and dilution of analyte concentration from sample digestion. In this work, a simple and robust approach coupling multiwall carbon nanotubes assisted matrix solid-phase dispersion (MWCNTs-MSPD) to single-drop solution electrode glow discharge-induced cold vapor generation (SD-SEGD-CVG) was developed for the sensitive determination of mercury in limited amount of sample. Mercury species contained in a limited amount of sample can be efficiently extracted into a 100 μL of eluent by MWCNTs-MSPD, which are conveniently converted to Hg⁰ by SD-SEGD-CVG and further transported to atomic fluorescence spectrometry for their determination. Therefore, analyte dilution resulted from sample preparation is avoided and sensitivity is significantly improved. On the basis of consumption of 1 mg of sample, a limit of detection of 0.01 μg L^-1 (0.2 pg) was obtained with relative standard deviations (RSDs) of 5.2% and 4.6% for 2 and 20 μg L^-1, respectively. The accuracy of the proposed method was validated by analysis of three Certified Reference Materials with satisfying results. To confirm that SD-SEGD-CVG-AFS coupling to MWCNTs-MSPD is a promising method to quantify mercury distribution in fish, this method was successfully applied for the sensitive determination of mercury in seven organs of common carps (muscle, gill, intestine, liver, gallbladder, brain, and eye) after dietary of mercury species. The proposed method provides advantages of minimum sample dilution, low blank, high sample introduction efficiency, high sensitivity, and minimum toxic chemicals and sample consumption.

Methods for the determination and speciation of mercury in natural waters--a review

This review summarises current knowledge on Hg species and their distribution in the hydrosphere and gives typical concentration ranges in open ocean, coastal and estuarine waters, as well as in rivers, lakes, rain and ground waters. The importance of reliable methods for the determination of Hg species in natural waters and the analytical challenges associated with them are discussed. Approaches for sample collection and storage, pre-concentration, separation, and detection are critically compared. The review covers well established methods for total mercury determination and identifies new approaches that offer advantages such as ease of use and reduced risk of contamination. Pre-concentration and separation techniques for Hg speciation are divided into chromatographic and non-chromatographic methods. Derivatisation methods and the coupling of pre-concentration and/or separation methods to suitable detection techniques are also discussed. Techniques for sample pre-treatment, pre-concentration, separation, and quantification of Hg species, together with examples of total Hg determination and Hg speciation analysis in different natural (non-spiked) waters are summarised in tables, with a focus on applications from the last decade.

Critical evaluation of the application of photochemical vapor generation in analytical atomic spectrometry

Chemical vapor generation (CVG) is a widely adopted sample introduction method for analytical atomic spectrometry. Nonvolatile precursors (usually ionic, metallic or organometallic species) can be transferred from the condensed phase to the gas phase, yielding the advantages of efficient matrix separation, high analyte transport efficiency, high selectivity, simple instrumentation, and ease of automation. Hydride generation enjoys the greatest popularity as a consequence of its ease of implementation, fast reaction and high yield; but photo-CVG, a newly emerging research field in analytical chemistry, may provide a powerful alternative to conventional CVG due to its simplicity, versatility and cost effectiveness. Although photocatalytic pre-reduction has been used for a number of years, the most attractive aspect of this newly emerging area is the direct generation of volatile species using photochemical reactions. Recent studies undertaken with flow through and batch reactors employing low molecular weight organic acids as photochemical agents are highlighted in this study for such systems as mercury and selenium, as well as reaction mechanisms considered for these processes. Discussion is focused on recent advances in photo-CVG, which we believe will become the subject of intensive future research initiatives.

Photo-induced cold vapor generation with low molecular weight alcohol, aldehyde, or carboxylic acid for atomic fluorescence spectrometric determination of mercury

With UV irradiation, Hg(2+) in aqueous solution can be converted into Hg(0) cold vapor by low molecular weight alcohols, aldehydes, or carboxylic acids, e.g., methanol, formaldehyde, acetaldehyde, glycol, 1,2-propanediol, glycerol, acetic acid, oxalic acid, or malonic acid. It was found that the presence of nano-TiO(2) more or less improved the efficiency of the photo-induced chemical/cold vapor generation (photo-CVG) with most of the organic reductants. The nano-TiO(2)-enhanced photo-CVG systems can be coupled to various analytical atomic spectrometric techniques for the determination of ultratrace mercury. In this work, we evaluated the application of this method to the atomic fluorescence spectrometric (AFS) determination of mercury in cold vapor mode. Under the optimized experimental conditions, the instrumental limits of detection (based on three times the standard deviation of 11 measurements of a blank solution) were around 0.02-0.04 microg L(-1), with linear dynamic ranges up to 15 microg L(-1). The interference of transition metals and the mechanism of the photo-CVG are briefly discussed. Real sample analysis using the photo-CVG-AFS method revealed that it was promising for water and geological analysis of ultralow levels of mercury.