An atmospheric-pressure microplasma jet source for the optical emission spectroscopic analysis of liquid sample

A miniaturized atmospherlic-pressure thermal plasma jet source has been developed as a sensitive detector of a portable liquid analysis system that can fulfil various requirements of 'on-site' analysis. The plasma source design required for achieving higher power transfer efficiency to the plasma has been studied mainly so that it can be operated with a commercially available compact VHF transmitter. The developed plasma device is a planar-type inductively coupled plasma (ICP) source that consists of a ceramic chip with engraved discharge tube and a planar metallic antenna with serpentine structures. Effects of chip materials and antenna designs on plasma characteristics are discussed based on the result of optical diagnostics of fine argon plasma jets produced with various prototype sources. Since the load impedance of the plasma jet is so small, it is necessary to contrive ways to lower the antenna impedance to attain higher power transfer efficiency. An atmospheric-pressure thermal plasma jet with a density of approximately 1 x 10(15) cm(-3) was successfully produced using a compact VHF transmitter at the 144 MHz VHF power of 50 W. The electronic excitation temperature of Ar was found to be 4000-4500 K. Moreover, the method of injection of the liquid sample into microplasma jets has also been investigated and preliminary results of the application to the analysis of tiny amounts of aqueous solution have been demonstrated.