Excitation/ionization process of aqueous solutions in high-power pulsed microplasma

Summary form only given. Atmospheric ICP (Inductively Coupled Plasma) has been widely used for elemental analysis because of its excellent excitation/ionization ability. In recent years, target of elemental analysis has shifted to smaller amount samples such as nano-particles and bio-cells. However, conventional ICP source consumes too large amount of plasma gas and sample (~1 mL/min). To realize efficient analysis of samples and high performance mobile elemental analysis system, we have studied and developed high-power microplasma source. With this device, stable plasma can be generated at a few watts of dc electric input power and with small amount of plasma gas (ca. 200 mL/min). However, input power was limited to a few watts because electrode will melt and damage. As a result, the plasma temperature and electron number density are not so high as that of ICP. Thus, the electrode must be protected from over heating to obtain sufficiently high analytical performance. To prevent electrode overheating and to generate powerful plasma, high-power pulsed microplasma was developed. With this device, very short (less than 1 mus) but high voltage (up to 3 kV) pulse is applied for plasma ignition, and then a long (about 10 mus) and relatively low voltage (up to 0.5 kV) pulse is applied for plasma sustainment and excitation/ ionization of analytes. Consequently, up to 40 kW of high- power electric input was achieved and aqueous sample introduction became available. 100 ppm yttrium aqueous sample was introduced with typical ultrasonic nebulizing system, and resulted in 100 ppb of detection limit based on Y(II) 371.03 nm. In this study, time resolved measurements have been done to reveal the sample excitation/ionization process in the microplasma. The sequential spectroscopic measurement was used and the temporal behavior of the excitation/ ionization ability of microplasma will be reported.