ICP Generation and Evaluation of Oscillation Frequency Shift Using Free-running RF-generator for Droplet Sample Introduction

Abstract

To decrease the amount of sample solution in ICP-AES/MS, we developed a new droplet direct injection nebulizer (D-DIN) system in which aqueous solutions were not nebulized, but injected into the plasma as a series of small droplets. The typical droplet volume is 700 pL, which that is about 100-times larger than the droplets in the mist from usual conventional nebulizers. In this study, for stable plasma generation under introducing large size droplets, we developed a free-running ICP generation system. To evaluate the frequency shift by changing the plasma impedance, the plasma generation conditions, such as the RF-power, plasma gas flow rate and carrier gas flow rate were changed and the oscillation frequency was measured. Upon increasing the RF-power, the oscillation frequency was increased to around 150 kHz for both Ar and He ICP. However, upon increasing the plasma gas flow rate, the frequency increased by 10 kHz in He ICP, and decreased by 20 kHz in Ar ICP. In addition, the frequency decreased by around 10 kHz Ar, and He ICP by increasing the carrier gas flow rate. These results suggested that this ICP generation system had sufficient following perfomance for fluctuation caused by large size sample droplet introduction into ICP.