Rapid aqueous sample extraction of VOCs: effect of physical parameters

Rapid aqueous sample extraction (RASE) devices were constructed and charact erized using m-xylene as a test analyte. Extraction of m-xylene from aqueou s samples was studied under many different conditions, independently varyin g extractor volume, extraction gas flow rate, temperature, pressure, sample volume, and sample concentration. Gas samples were analyzed as controls to determine the non-extraction (transport) component of the analyte pulse wi dth. The extraction of analyte from water to the gas phase took proportiona tely longer (compared to transport) for RASE apparatus that had a volume gr eater than 10 ml. An order of magnitude change in RASE volume resulted in l arger than an order of magnitude change in extraction time and total analyt e pulse width. The flow rate of the extraction gas had a much larger effect on a RASE apparatus with a volume greater than 10 ml. For these large extr actors, both extraction time and total analyte pulse width decreased by a f actor of 4 for a flow increase from 40 to 120 ml min(-1). There was little change at higher flow rates, or for extractors with smaller volumes. Temper atures below 40 degreesC resulted in large increases in the pulse duration due to broadening during transport. The temperature effect on extraction ti me was only a factor of 2 over a range from 25 to 85 degreesC. Pressure als o had only a relatively small effect, increasing extraction time and total pulse width by a factor of 2 over a range from 12 to 34 PSI. There was no o bserved change in either extraction time or total pulse width when the samp le volume injected varied from 10 to 1000 mul, or over a concentration rang e from 170 to 17 000 mug l(-1). RASE apparatus were capable of complete ext raction of analyte from water in less than 5 s under optimized conditions. (C) 2001 Elsevier Science BN. All rights reserved.