The background signals are very low and metal element emissions have the same optimum spectral emission positions in the plasma.

A solution-cathode glow discharge was used for atomic emission spectrometry. The acidic reagent, discharge current, and flow rate were optimized. The detection limits for sodium, potassium, calcium, and magnesium were 1.51, 4.13, 131, and 54.9 µg L⁻¹, respectively. The relative standard deviation for five replicates was from 0.52 to 3.00%. Sodium, potassium, calcium, and magnesium were determined in mineral water by solution-cathode glow discharge–atomic emission spectrometry. The results demonstrate that the protocol is suitable for the elemental analysis of mineral water.

In this study, we demonstrate a unique method for the detection of heavy metals such as chromium (Cr), copper (Cu), lead (Pb), and nickel (Ni) at trace levels in aqueous solutions via laser-induced breakdown spectroscopy (LIBS) enriched using chelating resin. Reduction in sample time preparation was shortened by tailoring the sample processing time with the aid of an enrichment method. The calibration curves and LODs of CH-90 chelating resin for enriching Cr, Cu, Pb, and Ni cations were established under the optimal conditions. The linear correlation coefficients were all above 0.98, and the detection limits were 0.148 mg/L, 0.150 mg/L, 0.149 mg/L, and 0.240 mg/L, corresponding to Cr, Cu, Pb, and Ni, respectively. The quantitative evaluation of the obtained results signifies that the proposed method is highly sensitive for detecting trace elements and offers a good correspondence of the acquired linear correlation with its calibration model. Results comparison with past studies suggests that the proposed method is able to achieve lower LODs for elements under investigation.

In this study, a refrigerating anode method was developed to improve solution cathode glow discharge-atomic emission spectrometry (SCGD-AES) for the determination of elements. Spectral characteristics of metal anodes at different temperatures were studied in the range from 10 to 30 °C. The spectral signals of metals were enhanced by reducing the metal anode temperature during the plasma discharge. Moreover, the method of the refrigerating anode improved the stability of spectral emission of metal elements. Compared with the unrefrigerated system under the same experimental conditions, the detection limits of Ag, Cd, Cu, Mn and Zn were 0.6, 9.1, 5.3, 8.7 and 16 μg L⁻¹, respectively, which represented the improvements by 6.5, 3.5, 3.2, 3.9 and 3.1 times, respectively. The measurement results of Ag, Cd, Cu, Mn and Zn in a certified reference solution (BWB2446-2016) and an actual water sample from the Yangtze river by SCGD-AES with the refrigerating anode were in agreement with the reference values measured by ICP-OES. The water sample recovery from the Yangtze river ranged from 101.5 to 110.0%, suggesting that the measurement results exhibited high accuracy and reliability. All the results indicated that SCGD-AES coupled with a refrigerating anode could improve its analytical ability and provide an analytical method for in situ, real-time and on-line determination of metal elements in water samples.

A hollow anode-solution cathode glow discharge (HA-SCGD) was designed as a plasma excitation source for optical emission spectrometry. The operation parameters such as the discharge current, argon flow rate and solution flow rate were investigated. The spatial distribution profiles of normalized results of spectral bands and spectral lines were investigated and analyzed. The detection limits of Na, Li, K, Ca, Mg, Pb, Sr, Mn, Rb, Cs and Zn were 0.22, 0.69, 1.33, 240.37, 21.55, 529, 619.43, 209.51, 2.94, 7.13 and 206.95 µg L⁻¹, respectively. The repeatability, expressed as the relative standard deviation for these elements, was determined to be within the range from 0.53 to 2.70%. The Ca, Fe, K, Mg and Na concentrations in a certified reference material were quantitatively analyzed, and the results obtained by the HA-SCGD system agreed well with the reference values. The results show that the HA-SCGD system accurately and stably determined metals in aqueous solution.