The plasma cell consists of two cylindrical electrodes on a fused silica capillary of 250 mm 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 21 . 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 CO 2 , CH 4 and ethanol vapour from the emission of C 2 at l ~385.2 nm in argon: the detection limits obtained were 90 ppb, 30 ppb and 33 ppb, respectively.

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The microplasma is implemented as an on-column optical emission detector. The arrangement consists of two cylindrical electrodes placed side by side on the fused silica separation capillary of 250 mm id and an optical fibre for coupling emitted light to a spectrometer. The plasma is generated with an ac voltage of 20 kV and 20 kHz by capacitive coupling of the energy into the capillary and can be sustained at flow rates employed in gas chromatography at atmospheric pressure. The detection of volatile organic compounds was possible via the emission from atomic carbon at 247.9 nm and from CN at 385.2 nm. Benzene, was determined with a detection limit of approximately 80 pg of carbon.

The microplasma detector consists of an unprecedented simple arrangement based on two cylindrical electrodes on a fused silica capillary which is operated with a high tension ac-voltage. Excellent sensitivity is achieved with optical detection for such species as pesticides.

A dual-beam near-infrared (NIR) spectrometer was constructed and evaluated. The instrument was designed to work with the two monochromatic beams produced by each one of the two acousto-optic tunable filters (AOTFs) evaluated, capable of scanning the wavelength range 800–1600 or 1500–2400 nm. Two temperature-controlled, cooled InAs detectors were employed for comparison of the two monochromatic beams produced by the AOTF. Data were obtained in a controlled ambient temperature, (25 ± 1) °C, and were compared for their intensity and wavelength coincidence for each of the 300 values of radio frequency (85–160 and 56–92 MHz) applied to the AOTF. The results show that the two beams present good concordance as a function of the wavelength (mean Δλ <0.30 nm) for both AOTFs investigated. The normalized intensities of the two beams were quite different, and their ratio values (0.9 to 1.2) depend on the wavelength. Inversion of intensities was observed in the present case and can be attributed to the unmatched position of the two detectors and to the difference in responsivity. On the other hand, the use of the two beams revealed that it can provide a robust way to correct for light-source intensity fluctuation as high as 10%. The mean standard deviation for long-term operation and for a zero absorbance baseline was reduced three times when the dual-beam instrument was employed. The instrument has also been evaluated for determination of water in fuel ethanol. The results for water content demonstrate the good analytical performance of the spectrometer with a relative error of 0.07 and 0.03% (w/w) for water determination in the ranges 0.20–10.0 and 0.20–3.00%, respectively.