Internal Standard Addition Method for Identifying Asbestos Containing Materials in Bulk Samples Containing Low Levels of Asbestos
This method was developed to overcome some of the limitations of standard PLM and TEM methodologies. The most widely used PLM and TEM methods rely on area ration estimation to determine asbestos concentrations and have limitations at low asbestos levels.
With this method a portion of the sample is weighed and added to an amount of asbestos different in type to that present in the sample, but equal in quantity to, a density adjusted 1% by weight. The quantification id performed via PLM visual comparison of the two types of asbestos and if necessary, by a modified point counting technique.
Compared to current methods, the "Internal Standard Addition" (ISA) method provides a significant increase in precision and accuracy as well as a reduction of false positives and false negatives in samples with asbestos content in the range of 0.25-5%