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

An atmospheric pressure glow microdischarge (μAPGD) 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-μAPGD system completely differed from those assessed for the noble gas-μAPGD system. Regardless of the applied microjet-supporting gas, cutting off the air supply caused a reduction of the NO and N2 molecular bands intensity, however, an apparent decrease in emission from analytical atomic lines was simultaneously noticed. Nevertheless, for μAPGD 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 μg L− 1 (for metals characterized by low emission, i.e. Cr, Pb), through tens (Ca, Co, Cu, Hg, Mn, Sr, Zn) and several μg L− 1 (Ag, Cd, Cs, In, Mg, Tl), to < 1 μg L− 1 for alkali metals (K, Li, Na, Rb). The measurement repeatability of μAPGD-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 μAPGD-OES was confirmed by analysis of ground water samples (ERM-CA615 and ERM-CA616).