Online mercury determination by laser-induced breakdown spectroscopy with the assistance of solution cathode glow discharge

Abstract

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.