New spray chamber for use in flow-injection plasma emission spectrometry

Abstract

The use of flow-injection analysis (FIA) in atomic emission spectrometry (AES) is often compromised by the relatively large dead volume and washout time of conventional nebulizer-spray chamber combinations. This problem is particularly acute when a microwave-induced plasma (MIP) is used as the AES source, because of the low flow rates ordinarily employed with an MIP and because of the limited tolerance of an MIP to solvent loading. In the present study, these problems have all been largely overcome through use of a novel spray chamber design and an MIP based on the microwave plasma torch (MPT). The MPT offers the advantages of a high tolerance to the introduction of aqueous aerosols, a central channel that exhibits enhanced energy coupling between the plasma and sample species, and low detection limits. A new low-volume spray chamber developed in our laboratory, coupled with the MPT, provides far shorter washout times than conventional units. Preliminary work on analyzing aqueous samples directly without desolvation has demonstrated that the use of air as a carrier has made it possible for a 200-μ1 injection volume to achieve the same sensitivity of detection as offered by continuous nebulization. Detection limits are in the range of 5-50 ng ml −1 for most elements studied. Also, the relative standard deviation (R.S.D.) for analyte signals is readily maintained at 2.5%. Organic solvents were also explored as the carrier for flow-injection analysis; under optimized conditions sensitivity dropped less than half for ethanol and by 40% for methanol, compared to performance with water as the carrier. This suggests the attractiveness of the new spray chamber-MIP combination as an element-selective detector for liquid chromatography (LC).