| Description |
Coupling hydride generation with atomic absorption or fluorescence spectrometry is a well-established technique for trace element and speciation analysis, enabling efficient, and matrix-free introduction of analytes into the detector. While heated quartz tube atomizers and diffusion flames remain the most widely used hydride atomizers, alternative plasma-based atomizers - particularly dielectric barrier discharges (DBD) and atmospheric-pressure discharges (APD) - have gained attention. The DBD can efficiently atomize As, Se, Sb, and Bi hydrides while reaching poor sensitivity for Pb, Sn, and Ge. In particular, Ge is detected with low sensitivity even in the most common hydride atomizers. Consequently, APD-based atomizers were developed and investigated in this work to overcome the low sensitivity observed in DBD for the elements mentioned above (Pb, Sn, Ge). Four APD designs were developed and tested. The first APD construction resembled the design of the diffusion flame, using a quartz capillary nested within a stainless steel anode and an opposing tungsten rod cathode. The zone of atomization was shielded with argon flow to prevent the entrance of oxygen from the ambient atmosphere. However, the discharge was unstable with this construction. The second design, based on two opposite rod electrodes, demonstrated stable discharge and obtained signal was comparable to that of diffusion flames. Thus, this design could be a robust alternative, and it is ready for optimization using an atomic fluorescence spectrometer. The other two APD designs tested were derived from the quartz tube atomizer. In the first arrangement, analyte hydride was introduced through a quartz and stainless steel capillary in a parallel direction with the plasma. In the second arrangement, analyte hydride was introduced through an inlet arm perpendicularly to the plasma and the opposite tungsten rod electrodes. The atomization area was protected from the ambient atmosphere by the optical tube eliminating the need for additional argon. The last design was selected as the most promising, and its performance was compared to the DBD and heated quartz tube atomizer. Current-voltage characteristics were evaluated, as they are crucial parameters for discharge performance. Due to the limited atomization efficiency achieved with commercially available high-voltage and direct current power sources, custom pulsed direct current power sources were developed. Various configuration will be presented. Moreover, the distribution and absolute concentration of hydrogen radicals/free analyte atoms in the most promising APD design were studied by two-photon/laser-induced fluorescence, and the results will be correlated with atomic absorption spectrometry experiments.
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