Interface-free integration of electrothermal vaporizer and point discharge microplasma for miniaturized optical emission spectrometer

Abstract

A tungsten coil (W-coil) as an electrothermal vaporizer (ETV) was interface-free integrated with a point discharge (PD) microplasma as an excitation source for a miniaturized optical emission spectrometer (OES). The PD microplasma and the W-coil ETV were vertically arranged in one quartz tube, and the W-coil was directly placed just under the PD without any physical interface. Working gas flow could sweep them successively to carry analytes released from the W-coil to the PD microplasma, and exhaust out of the quartz tube. The W-coil firstly acted as an ETV for sampling, on which pipetted with a tiny amount of sample solution (typically 10 μL), followed by a heating program for eliminating sample moisture and matrix. Vapor of analytes was subsequently released from the W-coil at a high temperature and immediately swept into the PD microplasma for excitation of atoms to obtain their optical emission spectra. Due to the high temperature of the W-coil, the released analyte species from the W-coil probably had been already atomized/excited partly and partially maintained prior to entering into the PD microplasma, thus saving the energy in the PD for sample evaporation and dissociation. In other words, the W-coil indirectly provided extra energy to the PD microplasma, thus its excitation capability was intensified. Under optimal experimental conditions, simultaneous determination of Ag, As, Bi, Cd, Cu, In, Pb, Sb and Zn was achieved, with LODs of 0.6, 45, 40, 0.08, 15, 8, 8, 41 and 5 μg L−1, respectively, and RSDs all less than 4.5% (n = 3, at corresponding concentrations of 5, 250, 250, 0.5, 100, 50, 50, 250 and 25 μg L−1). The accuracy validation of the proposed technique was demonstrated by successfully analyzing Certified Reference Materials (CRMs, including water, soil, stream sediment and biological samples), and preliminarily analyzing one CRM with direct slurry injection, both with satisfactory results, which had no significant difference with the certificated values at a confidence level of 95% by t-test.