Mechanisms in chemical vapor generation by aqueous tetrahydridoborate. Some recent developments in hydride generation

Metal tetrahydridoborates (Al, Be, Li) were firstly synthesized more than seventy years ago by Schlesinger's group at the University of Chicago and, soon after, NaBH4 was synthesized by Schlesinger and Brown. Although tetrahydridoborates were developed, at first, for wartime applications, they brought a revolutionary change in procedures for reduction of functional group in organic molecules [1]. In inorganic chemistry the use of NaBH4 was employed in the aqueous phase synthesis of volatile hydrides since 1954 and, much later, it was employed by Braman and coworkers as a sample introduction technique for ultratrace determination of Hg on 1971, and Sb and As on 1972, by atomic emission spectrometry [2]. The use of chemical vapor generation (CVG) of volatile species by aqueous NaBH4 is today a well consolidated technique for ultratrace determination and speciation by atomic and mass spectrometry. The mechanism of generation of volatile hydrides in CVG has been largely unknown for many years and only recently some dedicated investigation and a careful survey of chemistry literature allowed to drawn reaction schemes which are valid under ideal analytical reaction conditions (analyte at trace level, Boron/analyte ratio >103 mol/mol, pure aqueous solutions, optimized pH conditions) [2,3]. In the last years the attention has been focused on the definition of a reaction scheme which is of general validity both for both CVG under analytical reaction conditions and for conditions approaching those employed in synthetic reactions [4-6]. The collected experimental evidence allows to drawn a general reactions scheme for aqueous phase CVG of volatile hydrides which includes some possible reaction pathways at the origin of interference effects.