Additional data listed in Table 2 show the depth from which 90, 80 and 50% of the XRF signal originates. These data show that 50% of the K Kα fluorescence signal originates from the first 4 to 5 µm surface layer of the sample, with 80% of the signal from the top 10 to 11 µm layer and 90% of the signal from the top 15 µm layer.