Development of an element-selective monitoring system for adsorbable organic halogens (AOX) with plasma emission spectrometric detection for quasi-continuous waste-water analysis

An automated quasi-continuously-operating monitor has been developed for el ement-selective analysis of adsorbable organic halogens (AOX) in water. Aft er extensive optimization the automatic method was applied to the analysis of standard solutions and real waste water samples to prove its analytical applicability. The new instrument is based on the element-selective analysis of halogens b y means of a spectroscopic detection system consisting of a microwave-induc ed helium plasma excitation source (TM010-type; developed in this laborator y) and the plasma emission detector (PED) which operates with oscillating n arrow-band interference filters. After enriching the organic components on activated charcoal and pyrolysis in an oxygen stream at 950 degreesC, in ac cordance with DIN/EN 38409,H14/1485, interfering CO2 and H2O gas generated during combustion is removed from the analytes in the so-called ELSA-system (element-selective AOX-analyzer). For focused injection into the plasma ex citation source the analytes (hydrogen halides) are trapped in a deactivate d fused silica capillary at -180 degreesC; this is followed by identificati on and quantification on the basis of element-specific emission of radiatio n in the VIS and NIR-region (chlorine 837.6 nm, fluorine 685.6 nm). Bromine and iodine could not be detected with satisfactory inter-element se lectivity, because of spectral interferences caused by matrix elements, and so results from the respective single-element investigations for determina tion of AOBr and AOI are not presented. The procedure has been validated an d the analytical performance has been examined by calibration with p-chloro phenol and p-fluorophenol. The limit of detection was 1.1 mug (absolute) fo r chlorine and 6.6 mug (absolute) for fluorine.