The contribution of chemical vapor generation to the comprehension of the reactivity of aqueous boranes

Chemical Vapor Generation (CVG) play an important role in analytical chemistry in the determination and speciation o trace element Hg and hydride forming elements and, more recently, its use has been expanded to Cd, Zn, Cu and many other transition and noble metals. Analytical methods based on CVG are mainly based on the use of aqueous solutions of tetrahydridoborate salts (NaBH4 and KBH4) or, much less frequently, amine boranes R3N-BH3 (R=H, alkyl). Fundamental aspects related to of CVG have been the subject of many recent investigation and they are useful for the rationalization of the chemistry involved in the aqueous-phase reactions of borane with metal and semimetal inorganic substrates under various reaction conditions. In a real CVG system many other reaction pathways can take place simultaneously in addition to the analytical derivatization reactions, i.e. analyte-borane complex formation and hydride transfer from boron to analyte atom. In a sample solution containing the chemical species arising from sample dissolution, acids and buffers and chemical additives, the borane reagents can be involved in many different reaction pathways. In addition to the acid catalyzed hydrolysis the interaction of boranes with all the other chemical species which are present in the sample solution may led to formation of metal/semimetal nanoparticles, metal catalyzed hydrolysis of borane and formation of borane complexes, which play a decisive role in controlling the generation of analytical volatile derivatives. The recent investigation on CVG contributes to rationalization of the complex reactivity of aqueous boranes with metal and semimetal species and allows the reunification of CVG, synthesis of nanoparticles and the catalytic hydrolysis of boranes inside a common frame. The peculiar conditions employed in several analytical determinations, which are rarely used in fields other than CVG, allow disclosing some chemical behaviors which cannot be explained at the light of the reported reactivity of aqueous boranes.