NEW SPRAY CHAMBER FOR USE IN FLOW-INJECTION PLASMA EMISSION-SPECTROMETRY

The use of flow-injection analysis (FIA) in atomic emission spectromet ry (AES) is often compromised by the relatively large dead volume and washout time of conventional nebulizer-spray chamber combinations. Thi s problem is particularly acute when a microwave-induced plasma (MIP) is used as the AES source, because of the low flow rates ordinarily em ployed with an MIP and because of the limited tolerance of an MIP to s olvent loading. In the present study, these problems have all been lar gely overcome through use of a novel spray chamber design and an MIP b ased on the microwave plasma torch (MPT). The MPT offers the advantage s of a high tolerance to the introduction of aqueous aerosols, a centr al channel that exhibits enhanced energy coupling between the plasma a nd sample species, and low detection limits. A new low-volume spray ch amber developed in our laboratory, coupled with the MPT, provides far shorter washout times than conventional units. Preliminary work on ana lyzing aqueous samples directly without desolvation has demonstrated t hat the use of air as a carrier has made it possible for a 200-mu l in jection 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 devi ation (R.S.D.) for analyte signals is readily maintained at 2.5%. Orga nic solvents were also explored as the carrier for flow-injection anal ysis; under optimized conditions sensitivity dropped less than half fo r ethanol and by 40% for methanol, compared to performance with water as the carrier. This Suggests the attractiveness of the new spray cham ber-MIP combination as an element-selective detector for liquid chroma tography (LC).