A capacitively coupled microplasma in a fused silica capillary

Abstract

The plasma cell consists of two cylindrical electrodes on a fused silica capillary of 250 µm id and an optical fibre for coupling emitted light to a monochromator. 8 W of electrical power is coupled in using an ac voltage at 20 kHz and 20 kV. Impedance matching is not necessary at the relatively low frequency employed, and the low power means that the device can be operated from a battery. The plasma can be sustained with flow rates of argon or helium between 3 and 200 mL min⁻¹. The temperature, determined from the helium emission spectrum employing a Boltzmann plot, is approximately 12000 K. With this system it was found possible to detect mercury as vapour via atomic emission, as well as antimony and arsenic in aqueous samples via hydride generation. Also possible was the determination of CO₂, CH₄ and ethanol vapour from the emission of C₂ at λ = 385.2 nm in argon: the detection limits obtained were 90 ppb, 30 ppb and 33 ppb, respectively.