Reduction of spectral interferences in atmospheric pressure glow discharge optical emission spectrometry

An atmospheric pressure glow microdischarge (mu APGD) operated between a gaseous microjet and a flowing liquid cathode and sustained in various atmospheres (Ar, He, CO2) and in different discharge-systems (fully open to-air, semi-closed) was investigated by optical emission spectrometry (OES). The morphology of the emission spectra of all the discharges was discussed. The effect of the microjet-supporting gas flow rate on the intensity of the interfering molecular bands, emission from analyte atomic lines and spectroscopic parameters was thoroughly studied. It was noticed that the appearance, the electron number density, optical temperatures and behavior of the CO2-mu APGD system completely differed from those assessed for the noble gas-mu APGD system. Regardless of the applied microjet-supporting gas, cutting off the air supply caused a reduction of the NO and N-2 molecular bands intensity, however, an apparent decrease in emission from analytical atomic lines was simultaneously noticed. Nevertheless, for mu APGD operated in a semi-closed system, detectability of several metals (Cd, Co, Hg, Zn) evaluated with OES was improved twice. The obtained Limits of Detection (LODs) covered the range from hundreds mu g L-1 (for metals characterized by low emission, i.e. Cr, Pb), through tens (Ca, Co, Cu, Hg, Mn, Sr, Zn) and several mu g L-1 (Ag, Cd, Cs, In, Mg, Ti), to <1 mu g L-1 for alkali metals (K, Li, Na, Rb). The measurement repeatability of mu APGD-OES operated in the open-to-air system was below 1% and it was noticeably better than this received for the semi-closed system. The accuracy of mu APGD-OES was confirmed by analysis of ground water samples (ERM-CA615 and ERM-CA616). (C) 2016 Elsevier B.V. All rights reserved.