Glow discharge atomic emission spectrometry for the determination of chlorides and total organochlorine in water samplesviaon-line continuous generation of chlorine

Abstract

A method for the determination of ultratraces of chloride in solution by glow discharge atomic emission spectrometry (GD-AES) based on the evolution of molecular chlorine from chloride in an aqueous solution is described. Chloride conversion into volatile chlorine was achieved by continuous chemical oxidation in a flow system, the chlorine then being separated from the aqueous phasevia an on-line gas–liquid separator. Radiofrequency (rf) powered GD and direct current (dc) GD sources were investigated comparatively, while detection was performed, both in the visible (VIS) at 479.45 nm and in the near infrared (NIR) at 837.60 nm, using a charge-coupled-device. Discharge parameters affecting the emission intensity of chlorine (pressure and power) were investigated for both discharges with helium as the plasma gas. Once these parameters had been optimized, the corresponding analytical performance characteristics were evaluated. Rf-GD provided better detection limits (DLs) for chloride than the dc-GD (dc-GD, 2.5 ng ml^–1 in the VIS and 0.5 ng ml^–1 in the NIR; rf-GD, 1.0 ng ml^–1 in the VIS and 0.14 ng ml^–1 in the NIR). Finally, the method using rf-GD-AES and detection in the NIR was used successfully to develop a sensitive method for the determination of the adsorbable organic halogen (AOX) parameter in the wastewater from a cellulose factory in Asturias (Spain), after preconcentration and combustion steps to yield chloride ions from the organochlorides.