Studies in hydride generation atomic fluorescence determination of selenium and tellurium. Part 2 — effect of thiourea and thiols

In determination of selenium and tellurium by continuous flow hydride generation atomic fluorescence spectrometry, the effect of thiourea and thiols was investigated in view of their potential to achieve mild reaction conditions and as masking agents of interference from foreign elements. The effect of thiourea and thiols was first tested in the absence of interfering species and using different addition modes to reaction system. In the absence of interfering species, thiols negatively influenced the hydride evolution of both selenium and tellurium and, in general, they did not produce the desired effects. Thiourea was well tolerated in the determination of both elements by appropriate choice of experimental conditions. Possible mechanisms producing the depressive effect of thiourea and thiols were also investigated and are discussed later. Compromise reaction conditions were identified by using on-line addition of a neutral thiourea solution to acidified sample, combined with KI addition to NaBH4. Mild reaction conditions can be achieved by decreasing the NaBH4 concentration but at the expense of a reduced linear dynamic range. In the presence of foreign elements, thiourea allowed good control of interferences generated by Cu(II), Co(II), Ni(II), Au(III), Ag(I) and Bi(III). Tolerance limits could be improved by factors in the range of 7–2000, for both selenium and tellurium determination. The method has been successfully applied in the determination of traces of tellurium and selenium in copper, lead and molybdenum ores, stainless steel and pure copper metal without any additional steps other than sample dissolution.