Comparison of the performance of direct current atmospheric pressure glow microdischarges operated between a small sized flowing liquid cathode and miniature argon or helium flow microjets

Low power direct current atmospheric glow microdischarges were sustained between miniature Ar or He flow nozzle microjets and a small-sized flowing liquid cathode as new excitation microsources for optical emission spectrometry. The morphology of emission spectra of both microdischarges was compared and the effect of the flow rate of both gases on their performance and the emission characteristic related to molecular bands and atomic lines of selected metals (Ca, Cd, Cu, Fe, K, Li, Mg, Mn, Na and Zn) were studied using optical emission spectrometry. It was established that in the microdischarge with the miniature He flow microjet there were more convenient conditions for the quenching of the band emission originating from OH, N-2, NH and NO molecules as compared to those with the Ar microjet. The background level and its fluctuation in the vicinity of analytical lines of metals were lower, while their signal to noise ratios were higher. Under compromised conditions, selected figures of merit for the better microdischarge with the He microjet were evaluated. The detection limits assessed for Ca, K, Li, Mg and Na were within the range of 0.001 to 0.077 mg L-1. These metals were determined in six samples of tap water. The accuracy of this analysis, expressed as the relative error with reference to values determined with flame atomic absorption spectrometry (Ca, Mg) and flame atomic emission spectrometry (K, Li, Na), ranged from -2.1 to +10.1%. In addition, recoveries of metals added to the analyzed tap water samples varied from 90.6 to 106.9%. The precision of the analysis was within 0.2-4.6%.