Solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the direct determination of Hg in sludge samples Original Research Article

The present paper reports on the use of solid sampling electrothermal vaporization–inductively coupled plasma mass spectrometry (ETV–ICP-MS) for the direct determination of Hg in sludge samples. For `real-lifeʹ samples, the pretreatment was limited to drying, sieving and finally homogenization by means of shaking. One milligram amounts of the samples of interest were inserted into a graphite furnace coupled to a quadrupole-based ICP-mass spectrometer for subsequent analysis. The temperature programme of the graphite furnace was selected such that Hg was vaporized and transported into the plasma at a relatively low temperature (≈700°C). Under these conditions, co-volatilization of considerable amounts of the matrix, leading to signal suppression and hence, curvature of the mass response curve, could be avoided. Quantification was accomplished by means of external calibration, using a (solid) certified reference material, with a matrix composition comparable to that of the samples. The accuracy attainable was evaluated by means of (i) analysis of a sludge certified reference material and (ii) comparison of the ETV–ICP-MS result for a `real-lifeʹ sample with the aqua regia extractable Hg content, as determined by pneumatic nebulization ICP-MS after sample processing according to the German standard DIN 38414-S7. Although in all cases, the precision was observed to be limited by the inhomogeneous distribution of the analyte element over the matrix, the ETV–ICP-MS result obtained for the sludge reference material showed an excellent agreement with the certified value, while for the `real-lifeʹ sample, the average ETV–ICP-MS result agreed within 10% with the aqua regia extractable content. The approach developed was finally used for the analysis of sludges sampled at different locations in Limburg (Flanders, Belgium). For all but one sample, the Hg content was seen to be below the maximum allowable content, as specified in Flanders.