Rapid aqueous sample extraction of VOCs: effect of physical parameters

Rapid aqueous sample extraction (RASE) devices were constructed and characterized using m-xylene as a test analyte. Extraction of m-xylene from aqueous samples was studied under many different conditions, independently varying 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 width. The extraction of analyte from water to the gas phase took proportionately longer (compared to transport) for RASE apparatus that had a volume greater than 10 ml. An order of magnitude change in RASE volume resulted in larger than an order of magnitude change in extraction time and total analyte 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 extractors, both extraction time and total analyte pulse width decreased by a factor 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. Temperatures below 40 °C resulted in large increases in the pulse duration due to broadening during transport. The temperature effect on extraction time was only a factor of 2 over a range from 25 to 85 °C. Pressure also 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 observed change in either extraction time or total pulse width when the sample volume injected varied from 10 to 1000 μl, or over a concentration range from 170 to 17 000 μg l−1. RASE apparatus were capable of complete extraction of analyte from water in less than 5 s under optimized conditions.