DETERMINATION OF TRIHALOMETHANES IN AQUEOUS SAMPLES BY MEANS OF A PURGE-AND-TRAP SYSTEM WITH ON-SORBENT FOCUSING COUPLED TO GAS-CHROMATOGRAPHY WITH ELECTRON-CAPTURE DETECTION

A laboratory-built purge-and-trap device in which analytes desorbed fr om a primary trap (macrotrap) are focused in a microtrap (also with so rbent) and moisture is removed from purge gases by a Nafion tube (wall s selectively permeable to water vapour) is described. The device is c ompatible with capillary GC columns. Purge parameters such as purge ga s flow-rate and volume, purge temperature and ionic strength were opti mized with respect to recovery efficiencies of trihalomethanes (THMs) and carbon tetrachloride (CCl4) from aqueous samples. Sorption and des orption parameters of a macrotrap-microtrap system for THMs were selec ted. A procedure was developed whereby THMs and CCl4 at the level of s everal ppt can be determined with good accuracy and precision in a var iety of aqueous samples. The procedure was applied to the determinatio n of THMs and CCl4 in real samples, i.e., tap water, orange drinks and an infusion fluid.