An experimental study of the behaviour of several elements in inductively coupled plasma mass spectrometry using the single-bore high-pressure pneumatic nebulizer

Abstract

The behaviour of several elements using a new single-bore high-pressure pneumatic nebulizer (S) and a Meinhard nebulizer (M) in ICP-MS (VG PlasmaQuad PQ2 instrument) has been studied using the liquid flow, the gas flow and the relative distance (axial and transverse) from sampler to coil as variables for comparison. Drop size distributions of primary aerosols and transport rates have also been measured with both nebulizers. The results show that: (1) under the same conditions, nebulizer S provides finer primary aerosols and higher transport rates than M; (2) for any given set of experimental conditions, the signal ratios I S I M are different for each element, show smooth variations with the atomic mass of the element and do not seem to be related to the transport ratio (m A ) S (m A ) M , where m A is the amount of analyte transported to the plasma; (3) for many elements, an increase in the liquid flow causes a marked increase in the signal with either nebulizer, in spite of the fact that m A has decreased and the water load has increased; (4) the gas and liquid flows that maximize the signal are always lower for S than for M, and the optimized signals are 1.5 to 3 times higher for the former; (5) for both nebulizers, the variation tendencies of the signal for each element when the gas flow, the liquid flow or the sampler position is varied seem to be closely related to the atomic mass of the element. These results have been explained in terms of the “zone model” recently proposed by Vanhaecke et al. (J. Anal. At. Spectrom., 8 (1993) 433), which is based on the different rates of radial diffusion achieved by the ions from the central channel of the plasma according to their mass.