Formaldehyde passive sampler using an optical chemical sensor: how to limit the humidity interference

The behaviour of a new formaldehyde diffusive sampler using an optical chemical sensor with respect to high humidity conditions is examined in controlled atmospheres. Five prototypes of the radial diffusion sampler having the same chemical sensor and different designs were tested. In addition, a set of experiments were performed on the chemical sensor to characterise its efficiency of trapping water vapour in the absence and in the presence of the reactants, Fluoral-P and formaldehyde. Differences in humidity interference between the five diffusive sampler prototypes were studied and discussed. From all the results obtained, it was shown that the prototype LDE1.4 combining a small diffusion slot, a reduced internal volume and a sensor shifted upwards from the diffusion slot provided formaldehyde measurements least affected by humidity up to 80% RH at 20 °C. This new type of diffusive sampler with on-site direct reading is intended to ultimately replace conventional passive samplers with DNPH requiring offset laboratory analyses.