Combination of a multimode sample introduction system with a pre-evaporation tube to improve multi-element analysis by ICP-OES

Abstract

A pre-evaporation tube (heated to 400 °C) was inserted between a multi-mode sample introduction system (MSIS) and the plasma torch in inductively coupled plasma optical emission spectrometry (ICP-OES) to improve the simultaneous determination of hydride-forming and other elements. Multivariate optimisations were conducted to find operating conditions improving plasma robustness. Under these conditions and compared to conventional sample introduction with a pneumatic nebulizer and spray chamber, using MSIS with a pre-evaporation tube (PET) improved sensitivity and detection limits for hydride-forming elements (As, Sn, Hg, Sb and Bi) and other elements as well. In order to obtain a significant improvement for all elements, irrespective of hydride formation or not, the pneumatic nebulizer was replaced by an ultrasonic nebulizer (USN) and the same experimental conditions were used for the simultaneous introduction of aerosol and hydrides (from the MSIS) into a PET. With USN-MSIS-PET, the figures of merit of ICP-OES improved by over an order of magnitude for both hydride-forming elements and other elements compared to those with a conventional sample introduction system. Furthermore, using either PN-MSIS-PET or USN-MSIS-PET increased plasma robustness, likely as a result of the hydrogen gas by-product of hydride generation, which was reported to increase energy transfer within the plasma, and from the introduction of water vapor (with PET), which was reported to improve plasma stability as well as sensitivity. Good agreement with certified values was obtained when this approach was applied to the determination of hydride-forming and other elements in environmental certified reference materials.