Control of Precision in Head-space GC Determination of Volatile Organic Compounds in Water

It was found that the precision of the results of determination of volatile organic compounds (VOC′s) in water samples by GC using the HP 7694E head space automatic sampler was poor and unsatisfactory, and that the cause was the designing defect of its heating device. Measure for improvement was proposed by preheating the water samples to a temperature close to the temperature of the detection chamber (25±2) ℃ in water bath, and setting the conditions of head-space sampling at 55 ℃ and 15 min. Four VOC′s (i.e. CHCl3, BrCHCl2, Br2CHCl and CHBr3) were determined under the prescribed conditions. Values of RSD′s (n=5) found were in the range of 2.2% to 3.3%.