Development of ultrasound-assisted digestion methods for the determination of toxic element concentrations in ash samples by ICP-OES

Abstract

The present thesis introduces several ultrasound-assisted digestion methods developed for the determination of toxic element concentrations in ash samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Ultrasound-assisted digestion is a quite new technique used for sample pre-treatment purposes, especially in difficult sample matrixes. Elements determined are As, Ba, Co, Cr, Cu, Ni, Pb, Sb, Sr, V, and Zn. Most of the elements determined exist at a trace or ultra trace level in ashes and most are potential risks in the environment or human body even at low concentrations. Most of the selected elements can be determined directly by ICP-OES, but for the determination of Sb the hydride generation technique (HG-ICP-OES) is needed. The accurate analysis of As can be performed with the direct ICP-OES measurement and with the HG device. Several optimization procedures for digestion methods and ICP-OES measurements were performed. The homogeneity of ultrasound field in the water bath, the robustness of plasma conditions, the optimization of digestion time and the composition of acid mixture were investigated. Interferences of determination procedures were minimized by using matrix matched calibration solutions, optimized volumes of reagents and by performing the measurements under robust plasma conditions. The methods developed were evaluated by statistical tools, reference material and method, recovery tests and multiple linear regression technique. All the methods developed were tested with real ash samples. The suggested analytical procedures were summarised and achieved results were compared with other results published. This thesis is based on four scientific papers: two of them are more focused on the study of ultrasound-assisted digestion (I,II) and the other two are focused on investigations of interferences in the measurements and the determination of hydride forming elements (III,IV).