BACKGROUNDSolid sampling electrothermal vaporization (ETV)-inductively coupled plasma-mass spectrometry (ICP-MS) allows for a quick analysis of elements at ultra-trace levels and it is possible to minimize the time-consuming sample preparation step which may lead to second contamination or loss of samples. However, the simultaneous introduction of analytical elements, matrix components and solvents into the ICP may cause the spectroscopic and non-spectroscopic interferences. Fortunately, the matrix pyrolysis and analyte vaporization are separated temporally, interferences from the matrix can be reduced from temperature programs. Also, the introduction efficiency of the elements can be enhanced by using bypass gas from the outside of the ETV unit.

OBJECTIVESTo establish a rapid, efficient, and green pre-treatment technique and analytical method for accurate determination of heavy metals in large-scale on-site soil samples.

METHODSA high temperature electrothermal evaporating graphite furnace was used as the atomizer. After weighing, the sample was selectively evaporated by gradient heating, combined with two-channel heat transfer quartz tube, two-way argon online dilution, ICP-MS transient scanning, and matrix matching external correction, which effectively solved the problems of low transmission efficiency and a large matrix effect during direct soil sampling.

RESULTSUnder the optimized conditions, 20mg soil standard materials GBW07401, GBW07406, GBW07407, GBW07430 and GBW07456 were weighed to establish an external calibration curve. The linear correlation coefficient of the calibration curve of 7 elements in the sample was ≥ 0.999. The method was used to determine Cr, Cu, Zn, As, Cd, Hg and Pb in two field soil samples from the Binjiang District of Hangzhou City, which yielded a relative standard deviation of < 7%, relative error of < 2.5%, and a detection limit of 1.2-32.0ng/g, with recoveries of 91.0%-113.0%.

CONCLUSIONSThis method is a practical on-site sample analysis technology, suitable for the analysis and monitoring of large-scale soil samples in the field.