Dry ashing and microwave-induced plasma optical emission spectrometry as a fast and cost-effective strategy for trace element analysis

Microwave-induced plasma optical emission spectrometry (MIP OES) is combined with a simple dry ashing apparatus as a cost-effective alternative for trace element analysis. The Helios Rapid Ashing (HRA) prototype can reach up to 750 °C using a ceramic radiative heating element. It allows for sample decomposition in less than 5 min, and requires inexpensive sample holder materials such as aluminum foil and quartz fiber pads. Samples were decomposed at 500 °C and the analytes were extracted into a 10% v/v HCl solution before analysis by MIP OES. Limits of detection for Ca, Fe, K, Mg, Na and Zn were calculated as 2, 20, 30, 0.6, 2 and 5 μg/L, respectively. These analytes were determined in a certified reference material of Tomato Leaves (NIST SRM 1573a) and in challenging samples such as cheese, butter, peanut butter, infant formula and biodiesel. No statistically significant differences were observed between certified values and concentrations determined by the HRA-MIP OES procedure (t-test at a 95% confidence level). General agreement was also found between MIP OES results from samples decomposed either by the HRA or by a conventional microwave-assisted digestion procedure. MIP OES is an efficient alternative to FAAS, with comparable linear dynamic ranges and significantly improved sensitivity. It has short start/warmup times (ca. 20 min), runs on inexpensive N2, and may be a perfect match to the HRA system. The HRA-MIP OES procedure can be a simple, fast and accurate strategy for inexpensive and effective sample decomposition and trace element analysis.