Investigation of the direct injection high efficiency nebulizer for axially and radially viewed inductively coupled plasma atomic emission spectrometry

Abstract

A direct injection high efficiency nebulizer (DIHEN) is explored for introduction of the sample aerosol into the central channel of the axially and radially viewed inductively coupled plasma (ICP) of a commercial ICP atomic emission spectrometer (ICPAES). The DIHEN is a micro-nebulizer that requires very low solution uptake rates (1–100 µL min⁻¹) and nebulizer gas flow rates (<0.2 L min⁻¹) compared to conventional nebulizer-spray chamber arrangements (∼1.0 mL min⁻¹ and ∼1.0 L min⁻¹, respectively). Signal-to-background ratios (SBRs), detection limits, and precision of the DIHEN are comparable or superior to those of the conventional sample introduction system, but the Mg II 280.270/Mg I 285.213 nm ratios are lower with the DIHEN, indicating that the DIHEN is more susceptible to matrix effects than the conventional nebulization system, for both the axial and radial ICPAES systems. Matrix effects are further investigated by comparing intensity ratios with and without 0.1% and 0.5% Na for several spectral lines having energy sum ranging from 7.93 to 14.79 eV. Replacement of Ar with Ar–O₂ and Ar–N₂ mixtures in the outer gas flow of the plasma improves SBRs and Mg II 280.270/Mg I 285.213 nm ratios of the DIHEN, and reduces matrix effects. By reducing solution uptake rate from 60 to 30 µL min⁻¹, matrix effect is also reduced. Operation of the radial instrument at 1700 W reduces matrix effect compared to the effect noted for the axial instrument at 1500 W. Finally, the utility of the technique in practical ICPAES studies is demonstrated using a custom made organo-metallic standard for As, Hg, and Pb in xylene.