Mechanistic studies of hydride atomization and preconcentration in ambient plasmas for trace element analysis by atomic spectrometry
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| Year of publication | 2025 |
| Type | Requested lectures |
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| Description | Hydride generation (HG) is a useful sample derivatization step in trace element analysis being applicable to several analytically and toxicologically important elements including As, Se, Te, Pb, Sn Sb, Bi and Ge. It reaches almost quantitative and matrix-free analyte introduction into the atomic spectrometric detector. Hydride atomizers based on flame, heated quartz tube (QTA) or plasmas are employed in atomic absorption spectrometry (AAS). QTAs are the most common hydride atomizers in AAS offering high sensitivity universally for all hydride forming elements with the only exception of Ge, for which significantly impaired sensitivity is reached. Recently, ambient plasmas such as volume dielectric barrier discharges (DBDs) or atmospheric pressure glow discharge (APGD) have been reported to be an alternative to QTAs. Significant differences in sensitivity were found among individual hydride forming elements in ambient plasma-based hydride atomizers, especially in the DBD, even under atomization conditions optimized individually for each analyte. Since efficient hydride generation, i.e., analyte conversion to a corresponding binary hydride, has been proven for all hydride forming elements investigated in our previous studies, atomization mechanisms and the fate of free analyte atoms were investigated in this work using various advanced spectrometric techniques. Although DBD hydride atomizers offer either the same, or worse sensitivity than QTA, they allow simple and fast in-situ preconcentration of hydrides prior to AAS detection leading to significant LOD improvement. Laser induced fluorescence (LIF) was employed as a useful diagnostic tool capable of determination of spatial distribution of free analyte atoms in the atomizers, with or without the preceding in-situ preconcentration step, as well as quantifying their absolute concentration, leading to assessment of atomization efficiency. Hydrogen radicals were detected by two-photon absorption LIF (TALIF) as important species responsible for hydride atomization in all types of atomizers. Time-resolved optical emission spectrometry revealed the basic plasma dynamics. The analyte fraction deposited by decay reactions of free atoms at inner surface of the hydride atomizers was quantified by leaching experiments with ICP-MS detection while their morphology and composition were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. A detailed insight into the mechanisms of hydride atomization and preconcentration in ambient plasmas has been reached. The results found by these techniques are in perfect agreement with the observations made by AAS. Owing to a comprehensive approach based on a combination of advanced spectrometric methods, further improvements in the performance of DBD and APGD hydride atomizers will be feasible. |
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