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A novel atmospheric-pressure plasma source has been developed to determine metal ions in an aqueous solution by means of optical emission spectroscopy. In contrast to the conventional solution cathode glow discharge, this plasma source is sustained by a milli-second pulsed power supply. The electrical characteristics and spectral characteristics of the proposed plasma source are discussed. The effects of operating parameters, including pulse excitation and maintenance discharge voltage, pulse width, pulse modulation duty ratio, solution flow rate, and detector delay time, are investigated. Na, K, and Ca were observed to have a cumulative spectral emission time of 250 μs. Delayed acquisition times (in the case of maximum spectral intensity) are 500, 800, 800, 900, and 900 μs, respectively for Cu, Co, Cd, Mn, and Ag. The detection limits of trace elements such as Na, K, Cu, Co, Cd, Mn, and Ag were 0.080, 0.050, 3.4, 64, 69, 9.1, and 2.0 μg L−1, respectively. Compared to DC-excited solution cathode glow discharge, the detection performance of the above elements is observed to be increased by 2.9, 1.5, 18, 5.5, 25, 1.6, and 2.1 times, respectively. The proposed excitation source provides a promising method for detecting metal ions in aqueous solution samples. [ABSTRACT FROM AUTHOR]

The direct determination of analytes in aqueous solution using laser-induced breakdown spectroscopy (LIBS) has several difficulties, including low spectral signal, poor stability, and rapid quenching of the plasma. In this study, chelate resin and anion exchange resin were used to adsorb the chromium ions Cr(III) and Cr(VI) from the liquid onto a solid substrate, thus avoiding the drawbacks of liquid analysis with LIBS. Cr(III) and Cr(VI) were separated by selective adsorption on these two distinct resins. The following analytical parameters were optimized: flow rate of sample solution for preconcentration on the resins, laser pulse energy, and integral delay time of the ICCD detector. Calibration curves displayed excellent linearity, with correlation coefficients of 0.994 for Cr(III) and 0.993 for Cr(VI). The analytical limits of detection (LODs) were 0.088 mg L−1 for Cr(III) and 0.27 mg L−1 for Cr(VI), and were lower than those in most previous studies. The relative uncertainty of Cr(III) in single and mixed solutions ranged from 2.50% to 4.25% and 4.75% to 14.0%, respectively, and that of Cr(VI) ranged from 2.88% to 7.67% and 11.5% to 13.9%, respectively. Recovery from natural spring water was 92.50–99.86% for Cr(III) and 97.70–98.75% for Cr(VI). Recovery from sewage wastewater using this method was 99.80% for Cr(III) and 107.6% for Cr(VI). These results show that this method can be successfully applied to the determination and separation of chromium ions in aqueous solution. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Ferrous iron (Fe(II)) is essential to organisms, but ferric iron (Fe(III)) is toxic. Monitoring Fe(II) and Fe(III) in solution can improve our understanding of Fe biogeochemistry and toxicity. However, it is difficult to rapidly determine Fe in different valence states in solution using traditional methods. A novel method, laser-induced breakdown spectroscopy coupled with chelating resin selective enrichment by adjusting the solution pH, for determining Fe(II) and Fe(III) in solution is presented here. The sample solution flow rate and solution pHs were optimized to obtain a better enrichment effect. The calibration curve for Fe(II) and Fe(III) were established and the limits of detection were 0.120 mg L−1 and 0.142 mg L−1, respectively. Single valence state Fe in an Fe(II) and Fe(III) mixed solution was separated based on the enrichment abilities of Fe(II) and Fe(III) at different pH values of the chelating resin, and the separation relative error ranges were 0.25%–1.12% and 3.05%–7.24%, respectively. The recoveries of Fe(II) and Fe(III) in real spring water were 100.62% and 99.11%, respectively. The results indicated that the method of LIBS coupled with chelating resin selective enrichment can rapidly and accurately quantify Fe in different valence states in aqueous solution. [ABSTRACT FROM AUTHOR]

Herein, a pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) system was developed as a radiation source for the atomic emission spectroscope (AES) for metal element determination in aqueous solutions. The time-resolved emission spectra of the pulsed-ECAD were obtained at various frequencies, and their evolution behaviours during the modulation period were found to exhibit a strong dependence on the modulation frequency. The temporal behaviors of the metal element spectral intensities of K, Na, Li, Rb, Sr, and Mg as well as the atomic and molecular species emissions originating from water and air (OH, Hα, Hβ, N2, and O) were characterized from the plasma. The temporal evolutions of the pulsed-ECAD plasma parameters, including the rotational temperature, electron density, and ionization temperature, were analyzed. The results showed that the rotational temperatures varied between 950 K and 1350 K. The electron density and ionization temperature ranges of Mg were from 4.3 × 1014 to 2.2 × 1015 cm−1 and from 5200 K to 5500 K, respectively. [ABSTRACT FROM AUTHOR]

Solution-cathode glow discharge-atomic emission spectrometry (SCGD-AES) with a portable spectrometer was used to detect metal elements in solution. A modified pulsation damper was designed and optimized to improve discharge plasma stability. The effects of pulsation damper parameters as well as the discharge current and solution flow rate were investigated. The plasma stability of Na, K and Li elements under optimized parameters with the modified pulsation damper was discussed and they showed good stability over a long time. The standard deviation (SD) of background intensity was low, and the detection limits for Zn, Mg, Ag, Pb, Sr, Na, Li, K, Rb and Cs were 72, 2.1, 1.2, 35, 86, 0.04, 0.16, 0.14, 0.38 and 1.1 μg L−1, respectively. Ag, Zn and Pb elements in a certified reference material were quantitatively analyzed, and the measurement results obtained by SCGD-AES agreed well with the reference values. Specifically, the precision (relative standard deviation of 10 measured values) of detection was lower than 1.85%. The results show that the SCGD-AES system with the modified pulsation damper can accurately and stably detect the content of metal elements in water. [ABSTRACT FROM AUTHOR]

A novel atmospheric-pressure plasma source has been developed for the detection of metal ions in aqueous solution by optical emission spectrometry. In contrast to the common solution cathode glow discharge, this source is sustained by using an alternating-current power supply coupled with a high voltage diode. The electrical characteristics and spectral characteristics of this plasma source are discussed. The effects of operating parameters, including the acid anion, electrolyte pH, discharge voltage, discharge frequency, inter-electrode distance, sample flow rate and vertical distributions of spectral signals, are investigated. The spectral intensities and standard deviations (SDs) of background signals of this source are much lower than those of other electrolyte–electrode devices. In addition, metal element emissions have the same optimum spectral emission positions in the plasma. The detection limits of Li, Na, K, Rb, Cs, Sr and Mg are determined to be 0.0054, 0.0011, 0.0029, 0.04, 0.054, 2.5 and 0.26 mg L−1, respectively. The proposed excitation source provides a promising technique for the detection of metal ions in aqueous solution samples. [ABSTRACT FROM AUTHOR]

The trace mercury in an aqueous solution was determined by laser-induced breakdown spectroscopy (LIBS) with the assistance of a solution cathode glow discharge (SCGD) system. The aqueous solution was converted to the gas phase using a high voltage DC discharge, and then the generated mercury vapor was cooled by a gas–liquid separator to improve the concentration of the mercury. Finally, a 1064 nm wavelength Nd:YAG laser was used to produce the plasma. In the present experiment, the characteristic spectral line of Hg i 253.65 nm was selected for the analysis, under the optimal conditions of LIBS, to investigate the influences of the acid anion, the discharge current, the sample flow rate and the carrier gas flow rate. The temporal behavior of the electron temperature and electron number density were also investigated; the results show that the electron temperature decreases from about 10 900 K to 8800 K with a delay time from 200 ns to 6 μs and that the electron number density is in the orders of 1017 and 1018 cm−3, and decreases with delay time. The analytical performance of this method was evaluated under optimized conditions, and a calibration curve of Hg was plotted based on the different concentrations measurement results, and the detection limit (LOD) of Hg was calculated to be 0.36 mg L−1. By this experimental configuration, the detection limit and sensitivity of Hg are improved to some extent. This method provides an alternative analytical method for the measurement of trace mercury in water. [ABSTRACT FROM AUTHOR]