A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of toxic element concentrations (arsenic, barium, cobalt, copper, lead, nickel, strontium, vanadium and zinc) in ash samples was developed. All the measurements were performed in robust plasma conditions which were tested by measuring the Mg II 280.270 nm / Mg I 285.213 nm line intensity ratios. The highest line intensity ratios were observed when a nebulizer gas flow of 0.6 L min -1 , auxiliary gas flow of 0.2 L min -1 and plasma power of 1400 W were used for radially viewed plasma.The analysis of SRM 1633b showed that the ultrasound-assisted method developed is highly comparable with the microwave digestion method standardized by the United States Environmental Protection Agency (EPA-3052). The ultrasound-assisted digestion with a digestion solution of aqua regia and hydro fluoric acid (HF) resulted in recovery rates of over 81 %. One exception is arsenic which resulted in recoveries of about 60 % only; however, it could be digested with good recovery (> 90 %) using a digestion solution of 5 mL of water and 5 mL of aqua regia. The major advantage of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (30 samples simultaneously with a sonication time of 18 min).

A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element (chromium, copper, lead, nickel, vanadium and zinc) concentrations in fly ash samples was developed.All the measurements were performed in robust plasma conditions. Ultrasound-assisted digestion procedures using digestion solutions of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 80 % for all the analyte elements. Ultrasound-assisted twostep digestion with digestion solutions of 6 mL of HNO 3 (Step 1) and 3 mL of HNO 3 + 3 mL of HF (Step 2) resulted in recovery rates of over 92 % for all the analyte elements with one exception, chromium, which had a recovery of about 85 %. The analysis of SRM 1633bshowed that the two-step ultrasound-assisted digestion method developed resulted in chromium, copper, nickel and zinc concentrations higher than the microwave digestion method standardized by the United States Environmental Protection Agency (USEPA method 3052). This is the very first time when a digestion method using ultrasound resulted in higher efficiency than microwave (USEPA method 3052) for chromium and nickel in very hard to dissolve samples. The major advantages of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (about 30 samples simultaneously with a sonication time of 18 min) and the possibility to use new sample vessels without a significant increase in costs.

Hydride generation inductively coupled plasma optical emission spectrometry (HG-ICP-OES) was used in the determination of As and Sb concentrations in fly ash samples. The effect of sample pre-treatment reagents and measurement parameters used for hydride generation was evaluated. Due to memory effects observed, the appropriate read delay time was adjusted to 60s resulting in RSDs 0.6% and 2.3% for As and Sb, respectively. The most suitable volumes of pre-reduction reagents for 10 mL of sample were 4 mL of KI/ascorbic acid (5%) and 6 mL of HCl (conc.). The determination of Sb was significantly interfered by HF, but the interference could be eliminated by adding 2 mL of saturated boric acid and heating the samples to 60°C at least 45 min. The accuracy of the method was studied by analyses of SRM 1633b and two fly ash samples with the recovery test of added As and Sb. As high a recovery as 96% for SRM 1633b was reached for As using 193.696 nm with two-step ultrasound-assisted digestion. A recovery rate of 103% was obtained for Sb using 217.582 nm and the pre-reduction method with the addition of 2 mL of saturated boric acid and heating. The quantification limits for the determination of As and Sb in the fly ash samples using two-step ultrasound-assisted digestion followed with HG-ICP-OES were 0.89 and 1.37 mg kg(-1), respectively.

No abstract

No abstract