Effects of Droplet Introduction into the ICP Sustained by Free-running RF-generator on Plasma Spectroscopic Characteristics

Abstract

For stable plasma generation under introducing large-size sample droplets to ICP, we designed and developed free-running ICP. In the system, the impedance shift of the plasma generated by introducing the droplet is immediately cancelled by a shift of the RF resonant frequency of the entire system. To evaluate the shift of the frequency caused by changing the plasma impedance with introducing 5 nL droplets, the frequency shift in the free-running ICP was measured. In the case of Ar-ICP, the frequency increased by 17.3 kHz from the base frequency, and then returned to the base frequency in 130 ms. The excitation temperature was about 3000 K decreased and then became about 4000 K increased rapidly. When the same measurement was performed in the case of He-ICP, the resonant frequency decreased by 3.4 kHz, and then returned in 24 ms, the excitation temperature was about 500 K increased and then 1000 K decreased. In addition, the frequency fluctuation was increased due to droplet volume in both cases. The cause of the frequency-shift characteristics was also discussed by using an electric circuit simulation. The results showed that the difference of the frequency sifts tendencies between Ar and He ICP can be explained based on the cappling system for RF-power energy transfer.