Studies on end-on-viewed microwave plasma torch atomic emission spectrometry

In this paper, end-on-viewed microwave plasma torch (MPT) atomic emission spectrometry (AES) was studied in detail. In addition, by using the same experimental setup, a comparison of the analytical performance of the end-on-viewed MPT-AES system with that of the traditional side-on-viewed MPT-AES was made. A cut-off gas was adopted which was passed between the MPT and the lens to prevent the analyte from depositing on the lens and the heated gas from damaging the optical system. The effects of the operating parameters, such as carrier gas flow rate, support gas flow rate, microwave forward power and the temperature of the spray chamber in either system, were evaluated and compared. It was found that the optimal operating parameters for different elements were almost the same with the end-on-viewed MPT, while those with the side-on-viewed MPT were quite different. The end-on-viewed MPT was suitable for simultaneous multielement analysis without the need to compromise the operating conditions, which was, however, necessary for the side-on-viewed MPT. The analytical performance for twelve elements was also compared. The results indicated that the advantages of the end-on-viewed MPT include improved sensitivity and lowered detection limits and matrix effects as compared with the side-on-viewed MPT. The average improvement factor in the detection limits was found to be in the range of 3–10, the best being about 23. The narrower dynamic linear range caused by the hot tail of the plasma was a disadvantage.