Detection of brominated and chlorinated organics by a gas chromatographic microcoulometric detector : Effect of pyrolysis tube conditions

Abstract

The specific detection of halogenated organics is of considerable interest to environmental scientists. Low levels of organochlorine pesticides, polychlorinated biphenyls (PCBs), and polybrominated biphenyls (PBBs) entering the environment are important because of their refractory nature and potential for bioaccumulation. Low levels of some other halogenated compounds, such as haloforms, which are produced during the chlorine disinfection of waterre3 must be monitored because they may be directly ingested by humans. Gas chromatography (GC) with an electron-capture detector (ECD) is often used for the analysis of haloforms extracted from water&‘, as well as organochlorine pesticides, PCB, and PBB residues 6_ The ECD is used because of its sensitivity for halogenated compounds and its wide availability. The ECD has some disadvantages including: a lack of specificity; widely varying sensitivity with degree of chlorination, e.g. the ECD is 10’ times more sensitive to CHCI, than to CH,Cl (ref. 7); and sensitivity which varies with positional isomerism, e.g. different sensitivity for PCB isomers having the same degree of chlorination ‘. Microcoulometric detection does not have these disadvantages. The microcoulometric detector responds to the weight of halogen present. Through oxidative pyrolysis the material is converted to titratable halides which are swept into the microcoulometric detector cell where the halides react with the silver ions present in the cell electrolyte. The efficiency of this pyrolysis process varies with compound, pyrolysis temperature, and furnace atmosphere. The coulometer produces a voltage proportional to the current required to replace the consumed silver ions. The detector has a selectivity of IO6 for chlorine over carbon and of lo4 for chlorine over sulfur, nitrogen and phosphorusg. Microcoulometric detection has been used to measure total organic halogen as a water quality parameter using a system with a sample boat for sample introduction’*. In this paper the use of a commercially available microcoulometric detector specifically designed as a GC detector, the Envirotech (Santa Clara, CA, U.S.A.)