Spectrochemical Analysis by Using Discharge Devices with Solution Electrodes

Abstract

Solution electrode discharge instruments offer a low-cost, portable, small platform for fast spectrochemical analysis. (To listen to a podcast about this feature, go to the Analytical Chemistry website at pubs.acs.org/journal/ancham.) Solution electrode discharge systems are emerging tools in atomic spectrometry because they offer potential advantages over commercially and analytically successful plasma source techniques. They provide an alternative to nebulizer-based sample introduction, which is the Achilles' heel of plasma source spectrometry.

The improvement of the analytical performance of direct current atmospheric pressure glow discharge generated in contact with the small-sized liquid cathode after the addition of non-ionic surfactants to electrolyte solutions

“…From the very beginning, developed low power direct current (dc) APGD, operated between a metallic anode and an electrolyte solution that overflowed an inlet tube or a capillary, was characterized by a very simple design of the discharge cell and low operating costs [1][2][3][4][5][6][7]. Indeed, the electric power used to sustain the discharge is relatively low, i.e., within 20-80 W, and mostly dissipated at the liquid-discharge interface to evaporate water and sputter dissolved metal ions from analyzed solutions [8][9][10][11][12]. Despite a small size and a compact geometry of the discharge, excitation phenomena occurring in its near-cathode zone result in a simple atomic emission line spectra for a quite large number of metals, less common spectral overlaps of these lines and a relatively low level of the background intensity in their vicinity [1,2,11].…”

Roles of electrode material and geometry in liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma emission spectroscopy

“…Very different from the ELCAD-type devices where cathodic sputtering is proposed as the means of sample introduction [5,6,9], the ability to operate the LS-APGD solution as either the cathode or anode suggests that it is the thermal energy generated by charged particles crossing the solution/vapor interface that leads to vaporization. The heat generated is proportional to the discharge current, leading to greater vaporization rates.…”

“…A family of atmospheric pressure glow discharge devices shows promise in this regard. Currently, there are two basic designs that have been reported in the literature offering direct liquid sampling capabilities with multielement optical emission spectroscopy (OES) detection [5].…”

“…Kim et al reported limits of detection for various elements to be in the range of 0.01-0.03 ppm for the ELCAD device operating at 10 mL min − 1 , using unspecified analyte volumes [10]. A miniaturized version of the ELCAD has been reported by Hieftje and co-workers [5,[11][12][13] for high-throughput sampling in which limits of detection were found for Li (0.2 ppb) and Hg (270 ppb) for 25 μL samples [11]. These detection limits are promising, but the high sample introduction flow rates (2.5-3.5 mL min − 1 ) required for optimal operation make it difficult to couple the ELCAD instrument to many chromatographic systems and result in large volumes of chemical waste (predominately acidic aqueous solutions).…”

“…It is believed that the transformation of the bulk solution containing the analyte in nitric acid into the nebulized/droplet state occurs through a thermal process for the LS-APGD source; as opposed to the ELCAD devices where sputtering is stated to be the expulsion mechanism [5,6,8]. After passing into the gas phase, the plasma will affect the desolvation and vaporization of the residual particles.…”