Optimization of the gas stripping and cryogenic trapping method for capillary gas chromatographic analysis of traces of volatile halogenated compounds in drinking water

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method. it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene. and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry's law constants. To test response time the ST-GC-ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.

Choice and use of standards for dynamic headspace trapping and application to the analysis of the volatiles of baked potato

When attempting to quantify the volatile components of a food isolated by dynamic headspace trapping onto an adsorbent, the analyst has to select the most appropriate compounds to use as standards and at which stage of the analysis to add them. Factors to be borne in mind include the volatility of the standard, the response of the GC detector, and whether to add the standard to the sample or to the adsorbent trap. This chapter considers the issues and describes the application of one chosen method to the quantitation of the volatile components of baked potato.

Evaluation of purge-and-trap-high-resolution gas chromatography-mass spectrometry for the determination of 27 volatile organic compounds in marine water at the ng l(-1) concentration level

Purge-and-trap combined with high-resolution gas chromatography and detection by mass spectrometry was evaluated for the analysis of 27 volatile organic compounds (VOCs) in marine water samples down to ng l(-1) concentration levels. The target compounds included chlorinated alkanes and alkenes, monocyclic aromatic hydrocarbons and chlorinated monocyclic aromatic hydrocarbons and covered a wide range of VOCs of environmental interest. Limits of detection ranged from 0.15 ng l(-1) to 6.57 ng l(-1) for all VOCs, except for dichloromethane (41.07 ng l(-1)), chloroform (19.74 ng l(-1)), benzene (22.05 ng l(-1)) and 1,4-dichlorobenzene (20.43 ng l(-1)). Precision and accuracy were determined at a concentration level of 25.97 to 66.68 ng l(-1). Besides method validation, emphasis was put on quality control and assessment during routine determination of VOCs in marine water samples. Analytical quality control charts were plotted for all VOCs and a standard addition test was performed, as proposed by the QUASIMEME (Quality Assurance of Information in Marine Environmental Monitoring Programmes in Europe) working group. The analytical charts were incorporated in a working scheme containing guidelines to be applied during routine determinations, ensuring the long time reliability of the analytical method. Results yielded by the QUASIMEME interlaboratory exercise on organohalogen measurements in seawater are presented. The exercise was attended by seven out of eight laboratories who agreed to participate. Samples taken along the Scheldt estuary, from Breskens (The Netherlands) to Temse (Antwerp, Belgium) were analysed according to the developed technique. Concentrations as low as 0.33 ng l(-1) (1,2-dichloropropane) were detected near the mouth of the river Scheldt, while concentrations up to 326 ng l(-1) for tetrachloroethene and 461 ng l(-1) for cyclohexane were found in the vicinity of Antwerp.