Mechanisms involved in chemical vapor generation by aqueous tetra hydroborate(III) derivatization - Role of hexacyanoferrate(III) in plumbane generation

The role played by K3Fe(CN)6 (0.08 or 1.5 g l-1) in producing strong enhancement factors in the generation efficiency of plumbane in the reaction of NaBH4 (10 or 40 g l-1) with Pb(II) (50 ?g l-1) in 0.1MHCl solution, was investigated by using continuous flow chemical vapor generation coupled with atomic fluorescence spectrometry (CF-CVG-AFS). Different mixing sequences and reaction times of reagents were tested using different chemifold setups. Part of CF-CVG-AFS experiments were performed using the on-line, delayed addition of Pb(II) to a K3Fe(CN)6+NaBH4 reaction mixture. Kinetic calculations estimating the concentration of K3Fe(CN)6 remaining in the K3Fe(CN)6+NaBH4 reaction mixture before it merged with Pb(II) solution were also performed. Batch experiments measuring the amount of hydrogen evolved (pressure of H2 vs time) and pH variation during K3Fe(CN)6+NaBH4+HCl reaction were performed in order to have a correct estimation of the concentration of K3Fe(CN)6 remaining in the reaction system. The comparison of CF-CVG-AFS experiments with kinetic calculations indicates that strong enhancement factors of plumbane generation can be obtained without any interaction of K3Fe(CN)6 with Pb(II). The key role of K3Fe(CN)6 is recognized in its reaction with NaBH4 to give "special" borane complex intermediates, which are highly effective in the generation of plumbane from Pb(II).