Study on effect of introduced gas bubbles for the low channel damage in direct and alternating current liquid electrode plasma atomic emission spectrometry

Liquid electrode plasma (LEP) is used as an excitation source for compact and sensitive elemental analysis, where the channel damage by plasma causes the severe tradeoff between sensitivity and lifetime. In alternative current (AC)-LEP, significantly less channel damage (1/3000) was reported compared to direct current LEP (DC-LEP). However, the mechanism has not been clear. In this paper, the effects of external gas introduction into AC-LEP and DC-LEP were studied. The results showed that the external gas bubbles facilitated stable and highly sensitive plasma generation with lower power, reducing channel damage and increasing the lifetime of the analysis chip. These effects are significant in Ar introduction and AC-LEP cases. The facts suggest that the lower damage in conventional AC-LEP without gas introduction is attributed to H2/O2 bubbles generated by hydrolysis at electrodes and consequently introduced into the LEP from outside of narrow channel.