A portable solution cathode glow discharge-atomic emission spectrometer for the rapid determination of thallium in water samples
Graphical abstract
Introduction
Thallium,which is well-known as an extremely toxic heavy-metal element,is in a low-level content within the earth's crust [1]. However,with the development of mining and metal smelting,the release of thallium into the atmosphere is increasing and regional water thallium pollutions tend to be serious [2], [3], [4]. Besides,thallium can be remarkably accumulated in human tissues and organs by the food chain,and when the income of thallium exceeds a certain allowable content,great harms could be caused [5]. Therefore, it makes great sense to field and fast determine thallium in environmental water samples as the monitoring of the thallium pollution level is realized, and the thallium-poisoning risk can be decreased effectively as well.
At the present time, the determination of Tl (elemental symbol for thallium) is usually carried out by atomic spectrometry methods, such as atomic absorption spectrometry(AAS)[6], [7], [8],inductively coupled plasma-atomic emission spectrometry (ICP-AES) [9], etc. Although the sensitivity is ideal for the above means,matrix interference is serious and the analytic process is time-consuming for the graphite furnace(GF)-AAS method and spectral interference is prominent for the ICP-AES method due to the complicate emission spectral lines. In some works, the applications of inductively coupled plasma-mass spectrometry (ICP-MS) was used to improve the analytic performance [10], yet the instrumental operation is complicated and high-cost. Moreover, all the techniques above can’t be portable so that the demand of field test can’t be satisfied. Moreover, certain simple-instrumental electrochemical methods, such as anodic-stripping voltammetry, polarographic analysis etc, were reported in former study to detect Tl and showed good detection limits and precision [11], [12]. However, matrix effects were serious, and the electrodes were easily to be polluted and a tedious polishing treatment was demanded.
Solution cathode glow discharge (SCGD) atomic emission spectrometry has already reported as a novel technique to determine heavy-metal elements, including Pb, Cd, Cu,Hg,etc [13], [14], [15], [16], [17], [18]. and some methods were reported to improve the analytical sensitivity as well [19], [20], [21]. However, the determination of Tl has not been involved. In the SCGD system, metal electrodes are used as the anode while sample solution is employed as cathode. When a high voltage is applied, gas between the two electrodes will be ionized and the plasma will be generated. During the glow discharge process, the cathode solution is continuous gasified. As a result, the metal ions dissolved in the solution cathode also enters the plasma and was excited so that the emission spectrum comes into being [22]. In our work, the method for rapid detecting thallium by a home-made solution cathode glow discharger coupled with a fiber-optical spectrometer was established. The working conditions and parameters influencing the analytic performance were studied,after which the analysis capabilities were validated. The detailed spectra information of the interference could be acquired by an inside CCD detector of a fiber-optical spectrometer. This method is feasible for the rapid thallium determination in water samples. Besides, the SCGD apparatus we used is portable so that the field analysis is realized. What's more,only less dilute acid is needed for the test so that more chemical reagents could be saved, for which it's more environmental-friendly as well.
Section snippets
Reagents
All the acids were of guarantee grade (G.R., from Beijing Fine Chemicals Ltd.), Ultra pure water (>18.2 MΩ) was obtained from a Millipore ultra pure water system. Thallium standard stock solution (ICP-60N-1, 1000 mg L−1) was acquired from J&K Scientific Ltd. Calibration solutions ( 0.1 μg mL−1~ 5.0 μg mL−1) were prepared by appropriate dilution of the standard stock solution with 1%(v/v) hydrochloric acid. Besides, all the glassy wares were immersed in the 10% nitrous acid for 24 h and washed clean
The solution acidity
It has ever been reported that the discharge of SCGD-AES strongly depends on the pH of the solution due to the association between pH and cathode fall [23]. T.Cserfalvi et al. [24] observed the cathode fall as a function with pH and found that it was almost constant when the pH range was between 4 and 8, but significantly decreased when the pH was dropped to be below 4. The emission intensity is increased as the cathode fall decreases.
In our work, the influence of electrolyte cathode acidity on
Conclusion
The portable solution cathode glow discharge-atomic emission spectrometer is a novel technique to quantitatively and rapidly determine the trace amount of Tl. It offers the field detection of Tl at trace amount level an ideal alternative due to the high analytic performance and low spectrometric or matrix interference. It just takes about 1.5 min to complete the total analysis process of a sample, and no memory effect is observed due to the adequate washing process. Besides, SCGD-AES instrument
Acknowledgments
The authors are grateful to the support of (Beijing Municipal Science and Technology Project: Z161100003016008, Z161100003016010).
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2021, Analytica Chimica ActaCitation Excerpt :This is manifested by the small cross-sections of quartz, glass or ceramic capillaries delivering the analyzed solutions to the discharge zone (see in Table 1). Graphite tubes [12–38,61,65] (see Fig. 1A and B) or graphite cylinders [39–41] (see Fig. 1C) are inserted onto quartz capillaries [11–22,25,29,30,61,65], glass capillaries [23,24,26,27,31–40] or a ceramic capillary [28]. Graphite rods are also applied in few other systems but they are transversely mounted on glass or quartz capillaries through the holes drilled in them [11,42–48] (see Fig. 1D).