Our approach to Asbestos Analysis
Following recent enquiries regarding the comparability of asbestos methods we would like to offer a brief explanation of our approach. We feel it is important to highlight the benefits of using appropriate sample volumes.
Guidelines exist in various published and draft documents regarding the recommended sample size to be taken on site for asbestos analysis by a laboratory. In some cases 1 kg is mooted, and in some less, however within these and other guideline documents, very little guidance is given as to what constitutes a representative sample for detailed laboratory analysis. This is further compounded when the following limitation and interference with the quantification method is considered:
“As only a sub-sample is used for detailed gravimetric analysis, and also for free dispersed fibre analysis, there may be some issues with the representative nature of the sub-sample.” Draft SCA Blue Book for Asbestos, V9.
Considering samples for asbestos analysis are not mechanically homogenised as this would compromise the data, and analytical methods for chemical analysis using homogenised material typically use samples in the region of 10-20 g, it is a robust approach to take a larger sample size for non-homogenised analysis such as asbestos testing. Our accredited method suggests a sample mass of around 100 g depending on the sample matrix.
Using around 100g of soil for screening and quantification analysis means that the reporting limit (or LOQ) for this method, using an analytical balance (4 decimal places) is 0.001 %, equivalent to 1 mg of asbestos in the soil. It should be noted that lower weights on an analytical balance carry a greater uncertainty; hence the LOD is actually 0.0001 % with an LOQ of 0.001 %.
It is worth considering that for lower volume sub samples, the LOD may be compromised (e.g. 1 mg asbestos fibres in 20 g of soil = 0.005 % – Draft SCA Blue Book for Asbestos, V9).