AN INVESTIGATION INTO THE DIFFERENCES IN COMPOSITION OF FORMALDEHYDE ATMOSPHERES GENERATED FROM DIFFERENT SOURCE MATERIALS AND THE CONSEQUENCES FOR DIFFUSIVE SAMPLING

摘要

The results of an investigation into the differences in formaldehyde atmospheres generated from different source materials are presented. It was initiated after discrepancies were found between the results obtained from pumped and diffusive sampling methods when using formalin as the source material for formaldehyde atmosphere generation. The compositions of formaldehyde vapours produced from various source materials have been determined using infrared (IR) spectroscopy and chemical analysis. These showed that those atmospheres generated from paraformaldehyde yield almost entirely formaldehyde monomer, whereas those generated from formalin yield a mixture of formaldehyde monomer and methoxymethanol. This has the effect of varying the effective molecular weight of the formaldehyde species in the atmosphere, thereby changing the effective sampling rate of diffusive sampling devices. Results in this study suggest that there is a possibility that diffusive samplers will give erroneous results if they are used in field environments where the formaldehyde atmosphere differs in composition from that used in the laboratory calibration. This emphasizes the need to be certain of the nature and composition of any pollutant vapour in order that the sampling device can be appropriately calibrated.