Mechanisms of chemical generation of volatile hydrides for trace element determination (IUPAC Technical Report)

Abstract

Aqueous-phase chemical generation of volatile hydrides (CHG) by derivatization with borane complexes is one of the most powerful and widely employed methods for determination and speciation analysis of trace and ultratrace elements (viz. Ge, Sn, Pb, As, Sb, Bi, Se, Te, Hg, Cd, and, more recently, several transition and noble metals) when coupled with atomic and mass spectrometric detection techniques. Analytical CHG is still dominated by erroneous concepts, which have been disseminated and consolidated within the analytical scientific community over the course of many years. The overall approach to CHG has thus remained completely empirical, which hinders possibilities for further development. This report is focused on the rationalization and clarification of fundamental aspects related to CHG: (i) mechanism of hydrolysis of borane complexes; (ii) mechanism of hydrogen transfer from the borane complex to the analytical substrate; (iii) mechanisms through which the different chemical reaction conditions control the CHG process; and (iv) mechanism of action of chemical additives and foreign species. Enhanced comprehension of these different mechanisms and their mutual influence can be achieved in light of the present state of knowledge. This provides the tools to explain the reactivity of a CHG system and contributes to the clarification of several controversial aspects and the elimination of erroneous concepts in CHG.

Condensation cascades and methylgroup transfer reactions during the formation of arsane, methyl- and dimethylarsane by aqueous borohydride and (methyl) arsenates

“…Despite the widespread analytical application of volatile hydride formation for determination of trace amounts of elements such as arsenic, antimony, bismuth, germanium, tin, lead, selenium, tellurium and mercury the mechanism by which they are formed has been debated for many years. In particular, perpetuation of the notorious two-century-old incorrect hypothesis that free atomic (nascent) hydrogen is somehow involved in this reaction needs to be dispelled [4][5].…”

Non-chromatographic speciation of inorganic arsenic by atomic fluorescence spectrometry with flow injection hydride generation with a tetrahydroborate-form anion-exchanger

“…26 This work was not cited by the relevant analytical chemistry community until 2004. 27 More recently, all of the relevant chemistry has been set out in an 2011 IUPAC Technical Report, 28 in which the additional possible benets of the reaction between arsenite and L-cysteine to form thiol compounds of the form As(SR) 3 is considered. However, the reviewers conclude that it is the formation of the L-cysteine-borohydride complex is the key to sensitivity enhancement and interference control and that pretreatment to form arsenite-thiol complexes is not necessary.…”

Vapor generation – atomic spectrometric techniques. Expanding frontiers through specific-species preconcentration. A review

“…However the main reason lies on the generic principle of the technique involving analyte preconcentration and separation from the sample matrix resulting in a superior sensitivity and mainly, in a striking suppression of interferences during atomization [8].…”