Plasma discharges for trace element analysis - from their development to applications and mechanistic studies
| Authors | |
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| Year of publication | 2023 |
| Type | Conference abstract |
| MU Faculty or unit | |
| Citation | |
| Description | Volatile species generation (VSG) comprises a group of techniques based on analyte derivatization in order to form a volatile compound prior to detection. VSG coupled to atomic spectrometric detectors allows determination of metals at ultratrace levels. Chemical vapor generation (CVG) is the most common VSG approach resulting in selective analyte conversion from liquid to gas phase. Not only enhanced analyte introduction efficiency into the detector is reached, but also matrix separation is achieved leading to reduced risk of interferences. Moreover, VSG step can be utilized during speciation analysis or analyte preconcentration. VSG is compatible with all atomic spectrometric detectors including atomic absorption (AAS), atomic fluorescence (AFS) as well as inductively coupled plasma with mass spectrometric (ICP- MS) or optical emission detection (ICP-OES). The most common atomizers of volatile species are externally heated quartz tube atomizers (QTA) in AAS and diffusion flames (DF) in AFS. ICP torch is used in both ICP-OES and ICP-MS. Dielectric barrier discharges (DBD) have been recently proven a suitable alternative to QTA regarding atomization of volatile hydrides in AAS after CVG. The results of a comprehensive study focused on optimization of atomization conditions of Pb, Bi, Se and Te hydrides in DBD plasma hydride atomizer will be presented. Analytical performance of DBD atomizers in terms of sensitivity, limit of detection but also resistance to interferences will be compared to that of commonly used hydride atomizers for AAS, i.e. QTA and DF. Moreover, atomization of Ge hydride and its methylated analogues has been optimized employing DF, QTA and DBD atomizers. Interestingly, although Ge belongs to hydride forming elements, sensitivity of its determination by AAS is several orders of magnitude lower compared to other hydride forming elements (As, Se, Te, Pb, Bi, Sb or Sn). This might be caused either by poor atomization of GeH4 or fast decay of free Ge atoms, e.g. by reaction with oxygen. Laser induced fluorescence (LIF) has been used as a diagnostic method to reveal the fate of free atoms in DF, QTA and DBD. Owing to the LIF measurements the spatial distribution of free atoms can be visualized as well as their absolute concentration can be quantified leading to the estimate of atomization efficiency. The LIF results reached for three model analytes (Pb, Te and Ge) will be discussed. A simple and user-friendly preconcentration procedure was developed for As based on in-situ preconcentration of AsH3 in the DBD atomizer prior to its AAS detection. Analyte retention (trapping) occurs in the presence of oxygen admixed with the inert discharge gas (Ar) while analyte release (volatilization) is achieved by switching off the O2 flow in presence of H2 evolved spontaneously during VSG of blank. Application of this procedure to ultratrace speciation analysis of As was further developed. Four As species (iAs(III), iAs(V), MMAs and DMAs) were separated by HPLC to be subsequently treated by post-column VSG followed by in-situ preconcentration in DBD and AAS detection. Preconcentration efficiency exceeds 90% for all four As species while the system is fully automated. Analytical figures of merit and method validation by certified reference material of urine will be presented. |
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