Analytical performance of the Conical torch in axially viewed inductively coupled plasma optical emission spectroscopy

Abstract

The analytical performance of the new Conical torch compared with the conventional Fassel torch in axially viewed inductively coupled plasma optical emission spectroscopy (ICP-OES) is investigated under different conditions. The detection limits of 19 elements, effects of sodium content on analyte signals, and multi-element detection limits for both torches are determined under a wide variety of operating conditions. Also, a mathematical model, capable of predicting the effects of sodium concentration on the electron number density, signal intensity of other analytes, and plasma robustness, has been developed and employed to interpret the experimental findings. The roles of the injector tube internal diameter, power, and intermediate gas flow rate are studied. In terms of single- and multi-element detection limits, similar to the radially viewed results obtained previously, the Conical torch provides equivalent or better analytical performance than the Fassel torch, while working with 56% less gas and 50% less power, and having plasma at least 50% shorter in length compared to that of the Fassel torch. Additionally, the Conical torch is shown to be more resistant against interference from sodium. The decrease of the Mg signal intensity—due to 5.1% Na content—for the Conical torch is about 15% less than that of the Fassel torch using the same injector tube diameters of 2 mm, but with 500 W less power consumption. In contrast to an established belief in the literature, a collective analysis of the results indicates that using smaller—rather than larger—injector internal diameters is more helpful in suppressing the detrimental effects of sodium on the analyte signal intensity. In general, the Conical torch is expected to contribute to better accuracy and higher sensitivity in radially/axially viewed ICP-OES, with the added benefit of significant savings in gas and power consumption.