Determination of trace heavy metals in environmental and biological samples by solution cathode glow discharge-atomic emission spectrometry and addition of ionic surfactants for improved sensitivity
Talanta (Impact Factor: 3.55). 02/2014; 119C:613-619. DOI: 10.1016/j.talanta.2013.11.010
Solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) was evaluated for its ability to determine toxic heavy metals, including cadmium (Cd), mercury (Hg), lead (Pb), and chromium (Cr), in environmental and biological samples. A significant enhancement in heavy metal signal was observed by addition of a small amount of cetyltrimethylammoniumchloride (CTAC, C16H33 (CH3)3NCl) to the samples. The net intensity of atomic emission lines of Cd, Hg, Pb, and Cr increased by 2.1-, 4.8-, 6.6-, and 2.6-fold, respectively, after addition of 0.15% CTAC to the test solutions. The effects of ionic surfactants (CTAC) compared with non-ionic surfactants, e.g., Triton x-45 and Triton x-100, on the sensitivity of Cd, Hg, Pb, and Cr were also investigated in the present study. The enhancement effect is in the order Triton x-45<Triton x-100<CTAC for Hg, Pb and Cr and Triton x-45<CTAC<Triton x-100 for Cd. Addition of CTAC to the electrolyte solutions decreased the background intensity and fluctuation of atomic emission lines of studied metals. It also changed the surface tension and the viscosity, and increased average discharge current of electrolyte solution. SCGD sensitivity to the heavy metals greatly improved by addition of the surfactant. The improved detection limits of Cd, Hg, Pb, and Cr were 1.0, 7.0, 2.0, and 42ngmL(-1), respectively. The proposed method was validated by quantifying Cd, Hg, Pb, and Cr in certified reference materials, including human hair (GBW 09101b) and stream sediment (GBW 07310 and GBW07311). Measurement results obtained for the determination of Cd, Hg, Pb, and Cr in the reference materials agreed well with reference values. This study improves the application of SCGD-AES in quantifying very low levels of Cd, Hg, Pb, and Cr from biological and environmental materials.
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ABSTRACT: A theme that emerges from this year's Update is that of ‘green’ chemistry. This, in part, explains the larger than usual number of publications focussing on sample preparation, especially those concerned with the analysis of foods. Procedures that involved dilute acids while still achieving digestion of the specimens were reported by various workers. Meanwhile the trend towards smaller and smaller volumes continues with developments on the micro-scale. These aspects were noted in both the original work and in reviews. Last year saw the large number of papers concerned with metallic prostheses and this topic continues to attract interest. In possibly the first publication in which ICP-MS/MS was used for a clinical application, concentrations of Ti were determined in serum from healthy subjects and patients with hip implants. Concern is evident over the toxicological implications of consumption of rice grown in regions where water is contaminated with As. This has led to several reports of analytical methods and of concentrations in foods and total diets. Localisation of the As into different parts of the plant and the rice was also investigated and, in some reports this included speciation as well as the total As concentrations. Compared with the last few years, Se longer dominates the speciation work reported in this Update and there are more reports relating to As and Hg. A new class of arsenolipids, cationic trimethylarsenio fatty alcohols, were discovered in Capelin Oil. The number of publications applying XRF spectrometry to imaging elements within tissues appears to be increasing with localisation in bone of particular interest. Laser ablation ICP-MS in combination with other techniques, TOF-SIMS, XRD or XPS was also noted, to increase the information obtained.
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ABSTRACT: A direct current atmospheric pressure glow microdischarge (dc-[small mu ]APGD), generated between a miniature flow He jet nozzle anode and a small-sized flowing liquid cathode, was combined with a continuous flow cold vapor generation (CVG) system to improve the sensitivity of the determination of Hg by optical emission spectrometry (OES). In this arrangement, Hg(ii) ions were converted to cold vapor in the reaction with NaBH4 and subsequently delivered in a stream of He carrier/jet-supporting gas to the microdischarge through the nozzle anode. Additional He shielding gas was used to prevent discharge zones from the access of ambient air. A vertical distribution of emission from the Hg I 253.7 nm line between both electrodes was acquired, and the highest response for Hg was established in the near-anode region of the microdischarge. Several operating parameters that affect the CVG reaction and discharge were optimized. Under compromised conditions, the intensity of the Hg I line was improved over 4000 times compared to that obtained in a [small mu ]APGD-OES system without the CVG system. The efficiency of CVG of Hg and its transport to the microdischarge was evaluated to be 98 +/- 1%. For comparison, in the [small mu ]APGD system without CVG, the efficiency of sputtering was merely lower by about 20%, i.e., 77 +/- 4%. A likely explanation of the enhancement of Hg response observed for CVG-[small mu ]APGD was discussed. The detection limit (DL) of Hg assessed for CVG-[small mu ]APGD-OES was 0.14 [small mu ]g L-1 (3[sigma] criterion). To assess the accuracy of the new method, Hg was quantified in a certified reference material (CRM) of human hair (NCS ZC 81002). Excellent agreement between certified and measured concentrations of Hg was obtained. In addition, recoveries of Hg added to samples of different waters were evaluated. They were in the range of 96-103% proving the good accuracy of CVG-[small mu ]APGD-OES. The repeatability of the signal over the linearity concentration range of 5-500 [small mu ]g L-1 of Hg was within 2.1-4.1% (as relative standard deviation, RSD).
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ABSTRACT: This paper describes the quantitative measurement of trace elements in TiO2 powders using a modified solution-cathode glow discharge–atomic emission spectrometry (SCGD-AES) system. The optimal conditions utilized 0.1 M HNO3 sample solutions and operated at a voltage of 1060 V with a flow rate of 2.0 mL min−1. The TiO2 matrix concentration tolerance of the SCGD source was determined to be 10 mg mL−1. Sample solutions were prepared by dissolving different TiO2 powders using a high temperature acid digestion method. The values determined by SCGD-AES are comparable to those obtained using axial inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The proposed method was validated by quantifying Ag, Ca, Cu, Fe，K, Li, Mg，Na, and Pb in a certified reference material (NIST 154c), where the measurement results obtained by SCGD-AES agreed well with the reference values. In this method, Ti emissions were relatively weak, so that highly sensitive measurements of trace elements in TiO2 matrices can be conducted with little interference. The detection limits of the trace elements such as Ag, Ca, Cu, Fe，K, Li, Mg, Na, and Pb in TiO2 powders were 0.08, 2, 2, 5, 0.04, 0.02, 0.04, 0.02, and 0.4 g g−1, respectively. The enhancement of Pb sensitivity was also studied. Specifically, the limit of detection for Pb improved 6.5-fold to 2 ng mL−1 with the addition of 3% (v/v) formic acid.
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