Abstract: Abstract: The alkali solution extraction method is commonly used to extract hexavalent chromium in soils, according to the standard for Alkali Solution Extraction-Flame Atomic Absorption Spectrophotometry (HJ 1082-2019). This method has some problems for the detection of batch soils, including long extraction time, high reagent consumption, and large temperature variations. Therefore, it is highly desirable to develop a determination method of hexavalent chromium in soils with high efficiency and accuracy for risk assessments and remediation decisions of hexavalent chromium in soils. In this study, we developed a microwave digestion-flame atomic absorption spectrometry method of hexavalent chromium in soils. By conducting the effect experiments of extraction agents, microwave digestion conditions, digestion solution filtration treatments, we optimized the conditions for extracting and determining hexavalent chromium in soils. The digestion solution was composed of 20 mL of alkaline extract, 100 mg of magnesium chloride, 0.2 ml of dipotassium hydrogen phosphate buffer solution. Microwave digestion was conducted three times. The digested solution was filtrated with medium speed quantitative filter paper, and pH values of the solution were adjusted to 7.0-8.0. Under the optimized conditions, the observed concentrations of certified standard samples of soil were all within the range of standard values, and the recoveries of soil matrix spiked ranged from 85.5% to 88.7%, with the relative standard deviations of 7.6%-8.0%. Compared to the standard method of Alkali Solution Extraction-Flame Atomic Absorption Spectrophotometry (HJ 1082-2019), the method established in this study is suitable for the determination of hexavalent chromium in a large number of soil samples. Microwave digestion technology not only has high extraction efficiency, but also is technically facile and popular in different levels of laboratories. The method of microwave digestion-flame atomic absorption spectrometry proposed in this study will provide technical support for the rapid and accurate determination of hexavalent chromium in soils.
Keywords: alkali solution extraction; microwave digestion; hexavalent chromium; soils