Non-chromatographic Speciation Analysis of Tellurium by HG-ICP-MS/MS at Sub ng L-1 Concentration in Natural Waters Using TiIII as a Pre-Reducing Agent.

An automated and high-throughput (36 h-1) method for extremely sensitive determination of the two main tellurium species in the environment, namely, tellurite (TeIV) and tellurate (TeVI), was developed. Flow injection hydride generation was interfaced for the first time with inductively coupled plasma triple quadrupole mass spectrometry (ICP-MS/MS) detection to assure interference-free tellurium analysis. ICP-MS/MS conditions were studied in detail. Using a mixture of He + O2 gases in the reaction cell, the background signals significantly dropped and Xe isobaric interference was eliminated, allowing measurement with the most abundant Te isotopes, that is, 128Te and 130Te, and offering a huge increase in sensitivity. Volatile H2Te was selectively generated by a HCl/NaBH4 reaction from TeIV or from both TeIV and TeVI (TeIV+VI) after pre-reduction of TeVI by a TiCl3 solution. The optimum conditions for TiCl3 as a pre-reductant and the pre-reduction kinetics were also investigated. Different reduction rates were found depending on the sample stabilization media (HCl, HNO3, or EDTA). The same sensitivity was found for TeIV and TeVI, measured after pre-reduction, and no significant matrix effect was observed in both fresh and seawaters. Therefore, external calibration was used for quantification in real samples. Under optimal conditions, this method reached an unprecedented limit of detection of 0.07 ng L-1 for both TeIV and TeIV+VI and an intra-day repeatability of 5.2% at the 5 ng L-1 level. The methodology was successfully applied to the speciation analyses in commercially available certified reference materials of river water and seawater, and in bottled water and lake water samples.

Speciation of germanium in environmental water reference materials by hydride generation and cryotrapping in combination with ICP-MS/MS.

A method for the speciation analysis of the three main species of germanium in environmental waters, namely inorganic germanium (iGe), monomethyl germanium (MMGe) and dimethyl germanium (DMGe), has been developed. Germanium species were volatilized by hydride generation (HG) prior to their preconcentration/separation in a semi-automated cryogenic trap (cryotrapping, CT) and detection by ICP-MS/MS. A procedure to minimize the iGe blanks from the chemicals and water is reported. One mL of water can be analyzed without any pretreatment. After application of this procedure, and the careful optimization of all experimental variables, limits of detection (LOD) of 0.015, 0.005 and 0.003 ng L-1 have been obtained for iGe, MMGe and DMGe, respectively. Standard addition experiments did not show any significant matrix effect, and, therefore, external calibration was used for sample analysis. In the Tris-HCl + L-Cysteine reaction media, additional experiments did not reveal any significant demethylation of MMGe to iGe in the process of HG-CT, which could affect the accuracy of the analysis in seawater. The method has been applied to the analysis of iGe, MMGe and DMGe in certified reference materials of unspiked natural waters: CASS-4, CASS-5 and CASS-6 (nearshore seawater); NASS-5 and NASS-7 (seawater); SLRS-4, SLRS-5 and SLRS-6 (river water).

Speciation of gold nanoparticles and total gold in natural waters: A novel approach based on naked magnetite nanoparticles in combination with ascorbic acid.

A novel method for AuNPs/total Au speciation based on the combination of magnetic solid phase extraction and graphite furnace atomic absorption spectrometry (GFAAS) is described. Ascorbic acid enabled the quantitative extraction of both AuNPs and Au(III) by naked Fe3O4NPs, whereas a selective extraction of AuNPs was achieved in the presence of sodium thiosulfate. Experimental parameters influencing the extraction of both AuNPs and total Au, namely Fe3O4NPs mass, L-ascorbic acid concentration, pH, extraction time, sample volume, Na2S2O3 concentration and re-dispersion volume of magnetic solid phase prior to introduction in the graphite tube, were evaluated. Under optimal conditions, the proposed method yielded detection limits of 19.5 and 19.7 ng L-1 for AuNPs and Au(III), respectively. Intraday repeatability and inter-day reproducibility were lower than 5.3% (N = 6) and 7.6% (N = 4) for both species, respectively. Enrichment factors over 196, corresponding to extraction efficiencies higher than 98%, were obtained for both species. Remarkably, non-significant differences in the extraction of AuNPs over a wide range of AuNPs sizes and morphologies with different capping agents were observed. The reported method was applied to the analysis of superficial waters, groundwater, seawater and artificial wastewater with good recoveries. The method represents a suitable alternative to other reported methodologies for AuNPs quantification in environmental waters at (ultra)trace levels.

Headspace single-drop microextraction coupled with microvolume fluorospectrometry for highly sensitive determination of bromide.

This work reports on the development of a novel methodology for bromide determination by combining headspace single-drop microextraction with microvolume fluorospectrometry. The method lies in the in situ generation of bromine, transfer of the volatile to the headspace and trapping/reaction onto a fluorescein-containing aqueous drop exposed to the gas phase. The decrease in the fluorescence intensity enabled the determination of bromide without dilution of the enriched microdrop. Experimental parameters influencing the performance of the method, namely, fluorescence parameters, extractant phase composition, bromine generation conditions and microextraction time, were evaluated and controlled. Under optimal conditions, an enrichment factor of 243 was attained. The limits of detection and quantification achieved under optimal conditions for bromide were found to be 1.4 and 4.4µgL-1, respectively. The intra-day repeatability, expressed as relative standard deviation, was 4.4% (n=6). Besides, the inter-day reproducibility, performed at four different days, was 7.1%. Finally, the developed method was successfully applied to the determination of bromide in different water samples, showing recovery values in the range of 95-110%, and validated against certified reference material BCR-611 (ground water, Br- low level). The proposed method represents a highly convenient approach for monitoring of bromide at very low concentrations.