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RR981 - Accuracy of photo-ionisation detectors at high concentrations of volatile organic compounds

This project was designed to develop a system which will allow the generation of vapour fromselected VOC liquids at higher concentrations than can be supplied commercially in gas cylinders orfrom existing HSL systems, and to use this to investigate the accuracy of PIDs at these highconcentrations.

Attempts to create a static system of vapour production were unsuccessful.

Attempts to create a dynamic system of vapour production were moderately successful, the maximumconcentration of xylene vapour generated being 1720 ppm and the maximum concentration of toluenevapour generated being 3220 ppm. This method increased the range of xylene vapour concentrationsavailable by more than 100%. It did not, however, significantly increase the range of toluene vapourconcentrations. The output of the dynamic vapour generation system is linear and repeatable.

The accuracy of the PID at higher xylene concentrations was within 1% of the generatedconcentration and well within the documented instrumental tolerances of ±10% of the reading. Theworst case relative deviation in the results of 1.4% suggests that this method of vapour generation will be of a satisfactory level of consistency to allow the investigation of the operational characteristics ofa PID monitor at concentrations up to the limit of the generation system.

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Updated 2013-08-06