On-line monitoring of trihalomethane concentrations in drinking water distribution systems using capillary membrane sampling-gas chromatography

Trihalomethane concentrations are not typically monitored continuously in drinking water distribution systems. This means that data is not immediately available to operators so that they can make decisions that directly affect water quality. Monitoring data could be useful to researchers and operators who might want to better understand disinfection by-product formation and removal in their distribution systems. In this paper, a capillary membrane sampler (CMS), which uses a silicone membrane to directly sample trihalomethanes from a water sample, shows promise as a sampling device that can be used to introduce samples directly into a gas chromatograph for on-line monitoring. The construction, optimization, operation and evaluation of this capillary membrane sampling-gas chromatograph (CMS-GC) are discussed. The result of optimization, method detection limit, accuracy, precision and linearity studies are presented. Side-by-side studies have been done comparing the CMS-GC method to USEPA Method 502.2. While the CMS-GC method is not meant to replace USEPA Method 502.2, it does offer advantages for on-line monitoring and meets several of the criteria proposed as desirable for on-line monitoring of THM concentrations in drinking water distribution systems.