Chemical vapor generation atomic spectrometry using amine-boranes and cyanotrihydroborate(III) reagents

Amine-boranes of the type L-BH3 (L=NH3; ButNH2; Me2NH; Me3N) and sodium cyanotrihydroborate(III) (NaBH3CN) have been tested as derivatization reagents in the generation of volatile hydrides and elemental mercury following aqueous phase reaction with ionic species of Hg(II), As(III), As(V), Sb(V), Sb(III), Bi(III), Se(IV), Se(VI), Te(IV) and Te(VI). Continuous flow generation atomic absorption spectrometry coupled with flameless quartz tube atomizer (T=25°C) and miniature argon-hydrogen diffusion flame atomizer were employed for the detection of mercury vapors and volatile hydrides, respectively. All the reductants were able to reduce Hg(II) to the elemental state, giving sensitivities comparable to NaBH4 reduction. Under reaction conditions giving maximum sensitivity for hydride generation with NaBH4, only some amine-boranes are able to produce volatile hydrides from all the elements. No evidence of hydride formation was observed from the Se(VI) and Te(VI). In general, the reducing power decreased in the order NaBH4>H3N-BH3>ButH2N-BH3>NaBH3CN3 Me2HN-BH3>Me3N-BH3. In comparison with THB, amine-boranes and NaBH3CN allowed, in general, a better control of interference effects of Fe(III), Ni(II), Co(II) and Cu(II). Application to determination of mercury in certified reference material is reported. The most likely mechanism of reaction of borane complexes in chemical vapor generation is based on the direct action of hydrogen bound to boron.