2D simultaneous measurement of the oxyanions of P, V, As, Mo, Sb, W and U.

Previous work used the sampling technique diffusive gradients in thin films analysed by laser ablation mass spectrometry to measure sulfide, P, V and As at a microniche of reactive organic carbon in a freshwater sediment. Here we present new developments of this technique. The number of analytes has been extended and we demonstrate the technique for depth profiling of analytes in both one and two dimensions. The physical dimensions of the cell in the laser ablation unit restrict the maximum length of gel that can be analysed. We address this problem by proposing a method for obtaining better data continuity when analysing multiple segments of gel from the same probe. (13)C is used as the internal standard for each gel segment. For the cross-standardisation of different gel segments (58)Fe signals are obtained from ablation of a small piece of standard ferrihydrite gel analysed during the same run as the sample gel. As the ferrihydrite gel is a subsection of a much larger gel (i.e. the Fe concentration is consistent for all subsections), any difference in signal can be attributed to changes in detector sensitivity, allowing consistent standardisation of gels analysed in different runs and on different days.