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Abstract
Methodology was developed to unambiguously determine trace levels of volatile organic compounds as they vary in concentration over a variety of time scales. This capability is important because volatile organic compounds (VOCs) are usually measured by time-integrative techniques that average out peak exposures to insignificance. The specific method presented here involves a preprogrammed sequential syringe sampler that can fill 150-cm3 syringes with air at a rate of 2 to 90min per syringe. The 12 collected samples are then transported to the laboratory for fully automated gas chromatographic separation using mass spectrometric detection. The instrumentation and method are described, and representative results are given to document the variability in volatile organic compound (VOC) concentrations in situations such as use of household products and water outgassing in residential air, automobile indoor air during driving, and office indoor air that is subject to ventilation system cycling. The method is shown to perform automatically in both sampling and analytical modes. Contamination and sample integrity tests show typical precision to be about 10% relative standard deviation. Field tests show that VOC concentrations can vary by greater than an order of magnitude on different time scales, ranging from 2 min to 24 h.