Atomization of antimony hydride and in-situ preconcentration of antimony in a dielectric barrier discharge atomizer: A mechanistic study by laser induced fluorescence

Abstract

Background

Dielectric barrier discharge (DBD) ambient plasma has been recently used as hydride atomizers for atomic absorption spectrometry (AAS). DBD performance in terms of sensitivity has been proven comparable with the most common hydride atomizer, heated quartz tube (QTA), for some analyte hydrides while being significantly worse for the others. Moreover, a simple approach to analyte hydride preconcentration directly in the DBD (in-situ) prior to AAS detection has been reported with preconcentration efficiency significantly analyte-dependent. Detailed insights into the mechanisms of analyte hydride atomization and preconcentration are thus essential to utilize the full potential of DBD atomizers in analytical routine.

Results

Using SbH₃ as a model analyte hydride and laser induced fluorescence (LIF) as a detector, absolute concentration of Sb free atoms was quantified and their spatial distribution in the DBD discharge was visualized. The atomization efficiency of SbH₃ reaches (75 ± 20) % with homogeneous distribution of Sb free atoms in the whole DBD discharge area indicating long life of ground state free Sb atoms. In addition, the mechanisms of in-situ preconcentration of antimony in the DBD were investigated using LIF. The release of preconcentrated antimony from the inner quartz surface of the DBD walls was visualized and temporally resolved formation of free Sb atoms was acquired. Free atoms are firstly observed in the gas phase in the central part of the DBD, where they had been preconcentrated, having the character of a wave traveling towards the atomizer edges within approximately 2 s.

Significance

Both, high atomization efficiency and long life of free Sb atoms found by LIF prove perfect compatibility of DBD atomizer with AAS detection. This agrees well with high sensitivity reached in DBD atomizer in AAS which is comparable to that achieved in QTA. In preconcentration mode, spatio-temporally resolved LIF measurements revealed analyte trapping in a narrow spot in the central part of the DBD and enabled to study the dynamics of its subsequent release.