Improvement of Analytical Method for Heavy Metals in Sediment by Microwave Digestion

Abstract

To accurately measure heavy metals contained in sediment, we investigated a method of reducing the amount of residue by decomposing sediments using a microwave-assisted method, which has become increasingly popular in recent years. It is known that the addition of hydrofluoric acid is essential for the digestion of samples containing silicon, but it also produces insoluble white precipitates containing Ca, Mg, and Al. In this study, scanning electron microscopy (SEM) observation revealed that the precipitates produced in the microwave-assisted digestion of silica-sand-rich tidal flat sediment contained heavy metal elements such as Fe and Mn. With this information heat treatment with perchloric acid was introduced to the protocol to dissolve the precipitates. By applying this analysis method to various environmental samples, the contents of Cr, Cu, and Zn in the sediment samples were found to increase by 40%, 20%, and 18%, respectively, on average compared with a conventional method. The method studied in this research provides more accurate quantification of heavy metal contents in sediment and will be useful for establishing analytical methods in the future.