This study investigates the feasibility of using CCl4 in the background air as a concentration reference to calibrate synthetic mixtures. A metal vacuum line was constructed for preparing diluted standard mixtures at parts per billion by volume (ppbv) or trillion by volume levels (pptv) from pure substance. Component mixing ratios in the synthetic air were roughly estimated based upon the volume and pressure changes between the dilution glass bulbs on the vacuum line. More accurate estimates of the dilution factors relied on calibrating the absolute concentration of CCl4 in the synthetic mixture, acting as a surrogate, against its atmospheric levels. (C) 2000 Elsevier Science Ltd.