Efficient use of a conventional pneumatic concentric nebulizer in ICP-AES at low liquid uptake rates by applying a desolvation system: determination of detection limits and degrees of acid interferences

Abstract

A home-made, conventional glass pneumatic, concentric nebulizer has been used in radially viewed inductively coupled plasma atomic emission spectrometry for low sample consumption uptake rates, i.e., 50–200 µl min−1, by applying desolvation of the aerosol before it has entered the plasma. The desolvation system comprised a heated spray chamber and a condenser. The condenser temperature was 5°C and the cooling water was fed by a thermostatted water bath. The operating conditions, such as heating aerosol temperature, nebulizer gas flow rate and viewing height were established to achieve optimum signal-to-background ratios (S/B). Over the range of measured liquid flow rates, the highest S/B values of the low-energy atomic lines were obtained at a heating aerosol temperature of 80°C, while the best temperature was 120°C for the high-energy atomic lines and most of the ionic lines. At a liquid uptake rate of 102 µl min−1 and a heating aerosol temperature of 120°C, detection limits were reached which were similar to, or up to 10 times lower than, those which were obtained using the nebulizer in a common way, i.e., at a liquid flow rate of 1 ml min−1 and without pre-desolvation. Acid interferences of nitric and sulfuric acid, both in concentrations of 1.4 and 4.0 mol l−1, were studied. The interference seemed to be most serious for the low-energy atomic lines. To reduce the acid effect of the two nitric acid concentrations to within 10%, at liquid flow rates ranging from 50 to 100 µl min−1, heating aerosol temperatures of 160 and 200°C were needed for the measured ionic and low-energy atomic lines, respectively. The same interference reduction could even be achieved for the ionic lines of elements in a sulfuric acid solution of 4.0 mol l−1, provided the liquid uptake rate is not higher than 50 µl min−1.