Spatial inhomogeneity of metals in particulate matter on ambient air filters determined by LA-ICP-MS and comparison with acid digestion ICP-MS.

Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) has been used to examine the spatial distribution of metals in particulate matter on ambient air filters. The implications of the inhomogeneous distribution observed for the sub-sampling of such filters for multiple analyses have been discussed. It has been shown that large biases in measured values may occur unless the position and size of the sub-sample are chosen judiciously. Additionally, LA-ICP-MS has been compared against acid digestion ICP-MS as an alternative method for the determination of metals in particulate matter. It has been shown that the majority of variation in the LA-ICP-MS sensitivity accrues from small differences in the positioning of samples.