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

Abstract

A miniaturized atmospheric-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 × 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.

Current status of microplasma research

“…For this purpose, optical emission spectroscopy (OES) is combined with chromatography, in which a small amount of a liquid sample transferred by the electrophoresis effect in a capillary is taken into a micoplasma source, and the emission spectrum is analyzed for chemical constituents. In earlier days, a DC-discharge source with inner electrodes was used [52], but later ICP-type, coaxial type and microstrip-line type sources driven by high frequency power sources in a wide frequency range from RF to microwave have come to be used [53][54][55][56]. A micro-HC type DC source is also going to be used owing to its high plasma density [37,57].…”

Sample Analysis with Miniaturized Plasmas

“…Small microfabricated ICPs (mICP) have also been developed in recent years. [16][17][18][19][20][21][22][23][24][25][26] Whereas large ICPs are typically operated at a frequency of 13.56 MHz, it has been shown that the optimum frequency for plasma generation increases to 460 MHz when the coil diameter is reduced to 5 mm. 17 It was found that the electron density increases with the frequency and is about an order of magnitude higher than in a large scale ICP as a result of the large surface-to-volume ratio of small discharges.…”

“…26 Prototypes of injector devices were located at the downstream position of the plasma source chip and sample injection into the radial direction of the plasma jet was attempted. In preliminary experiments it was found that better injection performance was attainable for the electrospray injection.…”

A hypersonic plasma bullet train traveling in an atmospheric dielectric-barrier discharge jet

“…4,5 These plasma sources can be generated with sinusoidal excitation at 60 Hz, 6 kHz, 5,[7][8][9][10] MHz, 1,4,[11][12][13][14] and with repetitive nanosecond pulses at kilohertz. 8,15 For many of their applications, nonthermal plasma jets offer a useful practicality of separating the plasma generation region from the application region thus facilitating access to an extensive range of reaction chemistry.…”