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The Recovery of Material Deposited on Filters
The development of an airborne concentration standard is required to allow the complete calibration of analysers that measure particle size distributions. To date, it has been generally assumed that the ability of such instruments to measure airborne particle concentrations is constant across the measurement range of the instrument. However, there are a number of processes (e.g. sampling efficiency, aerosol transport efficiency and detection efficiency) which vary with varying particle diameter and may affect the efficiency with which particles of various sizes are measured. In the standard currently under development, an aerosol of well-defined test particles will be generated and simultaneously sampled by the analyser under calibration and onto a filter to provide a reference airborne concentration. Thus, the use of a filter sample as the reference measurement to determine the aerosol concentration would constitute the fundamental aspect of the technique. The recovery of the material deposited on the filter must be complete and repeatable; thus, the chemical composition of the aerosol particles and the technique to recover and analyse the deposited material must be carefully chosen and validated. This work assesses the suitability of three candidate materials, viz. polymer latex, methylene blue and fluorescein for this purpose.
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