Determination of diborane by adsorption sampling using modified silica gel and the chromotropic acid-HPLC method.

A method for determining atmospheric diborane in concentrations higher than 1/10 of TLV, i.e., 0.01 ppm, has been developed using the adsorption sampling method. Silica gel impregnated with potassium permanganate, synthetic resin activated carbon impregnated with or without mercury(II) chloride and activated carbon impregnated with chromate salt showed adsorption capacities larger than 18 l of 3 ppm diborane test gas when the test gas was drawn at 300 ml/min. Complete desorption of the adsorbed diborane was possible only from silica gel impregnated with potassium permanganate into a hydroxylamine hydrochloride solution. As methods for determining the desorbed boron, both the chromotropic acid-HPLC method and ICP-AES were applied. The former was more sensitive, but the latter was less influenced by coexistent substances. The most sensitive and reproducible procedure for diborane determination was as follows: diborane is collected with silica gel impregnated with potassium permanganate (0.05% (w/w)) and desorbed into hydroxylamine hydrochloride solution (400 micrograms/ml) followed by the determination of boron by the chromotropic acid-HPLC method. When diborane in 3 l of 0.1 ppm test gas was collected, the desorption efficiency was 105.3% with an RSD of 13.5%. The limit of quantitation of this method was 0.0026 ppm in 3 l air. Much lower concentrations can be determined by sampling larger amounts of air.