Rhenium-cup, in-torch vaporization (ITV) sample introduction for axially viewed ICP-AES and its application to the analysis of a microscopic, ng-weight solid sample

Abstract

A reported advantage of axial over radial plasma viewing is improvement of detection limits. In an attempt to capitalize on this advantage, a new, horizontally operated in-torch vaporization (ITV) sample introduction system was developed and was coupled to an axially viewed inductively coupled plasma-atomic emission spectrometry (ICP-AES) instrument. In ITV, a sample is placed into a cup made out of a thin rhenium (Re) foil and the sample-carrying cup is inserted in a small volume vaporization chamber that clips onto a typical ICP torch. The effect of carrier gas (Ar–∼3% H₂) flow rate and cup insertion position on analyte emission characteristics was examined for several elements (e.g., Ba, Be, Ca, Cd, Mg, V, Pb and Zn) that had different vaporization characteristics and emission lines that covered a wide spectral range (e.g., from 213.856 to 455.403 nm). Calibration curves were linear over the (narrow) range of concentrations used in this work and precision ranged between 1.0 and 2% (peak height) and between 1.0 and 4.6% (peak area). Detection limits were in the pg range for Pb, Cd and Zn, in the sub-pg range for Ba, Mg and V, and in the fg and sub-fg range for Be and Ca. The improvement in detection limits enabled determinations of Ca and Mg in microscopic individual grains of pollen (10 pL volume, ∼8 ng weight).