Evaluation of a direct injection high-efficiency nebulizer (DIHEN) by comparison with a high-efficiency nebulizer (HEN) coupled to a cyclonic spray chamber as a liquid sample introduction system for ICP-AES

Abstract

In the present work the advantages and limitations of introducing the sample directly into the plasma through the use of a direct injection high-efficiency nebulizer (DIHEN) have been evaluated in ICP-AES. The reference system was a high-efficiency nebulizer (HEN), precursor of the DIHEN, coupled to a cyclonic spray chamber. It was found that the plasma can only be operated under non-robust conditions because of the high solvent loading. The issues considered in the present work were: (i) the aerosol characteristics; (ii) the ICP-AES analytical figures of merit; and (iii) the interferences induced by the presence of inorganic as well as organic matrices. The results indicated that the aerosols obtained by the DIHEN are coarser than those leaving the cyclonic spray chamber. Nonetheless, and due to the higher analyte transport efficiency, the DIHEN affords ICP-AES sensitivities and LODs up to 10–18 times better than the cyclonic spray chamber. Also, it was found that, under the plasma conditions tested, the optimum nebulizer gas and liquid flow rates in terms of sensitivity for the DIHEN were very different from those for the HEN with the cyclonic spray chamber. In the first case, the signal peaked at rather low liquid (Ql) and gas (Qg) flow rates, whereas for the cyclonic spray chamber moderate and/or high liquid and gas flow rates were advisable. Under a given set of plasma conditions, the DIHEN has been proven to produce problems due to deterioration in the plasma, derived from the higher solvent load with respect to the HEN coupled to the cyclonic spray chamber. Despite these findings and the fact that a non-robust plasma was used, the matrix effects for inorganic and organic species were significantly minimized, for a low Ql and for some lines, in the case of the DIHEN.