Determination of halides by microwave induced plasma and stabilized capacitive plasma atomic emission spectrometry after on-line continuous halogen generation

This paper describes a comparative study of the microwave induced plasma (MIP) and the stabilized capacitive plasma (SCP) for halide determinations. The MIP is generated in a Beenakker cavity TM010 using a tangential flow torch and the SCP consists of a 27.12 MHz discharge sustained in a liquid-cooled, fused silica tube surrounded by two annular electrodes. Both discharges are operated in helium at atmospheric pressure and detection was carried out by Atomic Emission Spectrometry (AES). The halides (I-, Br-, Cl-) are converted to volatile halogens by continuous flow generation based on chemical oxidation and on-line separation from the aqueous phase, via a gas-liquid separator, to be finally introduced into the plasma. The different factors affecting the emission intensity of the volatile halogens generated are compared for both discharges and the analytical performance characteristics are also evaluated. Detection limits of 17 ng ml(-1), 24 ng ml(-1) and 55 ng ml(-1) are obtained for the determination of Cl-, Br-, and I-, respectively, in the ultraviolet-visible (UV-VIS) region using the MIP-AES and 45 ng ml(-1), 135 ng ml(-1) and 400 ng ml(-1) for Cl-, Br-, and I- with the SCP-AES. Lines in the near infrared (NIR) region were also evaluated for the SCP-AES detection; improvements in detection limits higher than 30 times were observed in the NIR region as compared with the UV-VIS with detection limits in the NIR of 1.4 ng ml(-1) for Cl-, 3 ng ml(-1) for Br- and 13 ng ml(-1) for I-. (C) 1997 Elsevier Science B.V.