Effect of Easily Ionisable Elements on the Mass Transport Efficiency of Solutions and Slurries Used in Plasma Emission Spectrometry

Abstract

The effect of easily ionised elements (EIEs) upon the mass transport of solutions and slurries used in plasma emission spectrometry has been directly measured. Solutions and slurries of 1000 µg ml ^-1 Mn ²⁺ and MnO ₂ (equivalent to 1000 µg ml ^-1 Mn), respectively, were aspirated at a carrier gas flow rate of 1 l min ^-1 through a V-groove nebuliser, double-pass spray chamber and injector system in the presence and absence of equimolar amounts (0.05 m) of Li, Na, K and Cs. The aerosol exiting the 2 mm bore injector was directly collected and the analyte of interest (Mn) was determined using a titrimetric technique. The mass transport efficiency of an Mn only solution was found to be 1.33%. This efficiency decreased, when Li was added, to 90% of the solution only value, and down to 45% of this value when Cs was present. The mass transport decreased in the order Mn only >Li>Na>K>Cs. As equimolar amounts of the EIE were present, the effect is attributed to the total mass of the matrix present and not to the matrix being an EIE. The MnO ₂ slurry showed the same effects in the presence and absence of EIEs. Larger solid particles (>3–4 µm) in the slurry resulted in a mass transport efficiency of 0.95% when no EIE was added. This decreased to 35% of the slurry only value when Cs was added. The mechanism for this decrease, together with the importance of matrix loading upon mass transport when determining EIE effects from intensities of concomitant analytes directly from plasma instruments, are discussed.