Highly Sensitive Low Temperature Fractionation Method for Separation and Measurement of Boron Hydrides

Abstract

A highly sensitive method capable of detecting quantities of the boron hydrides, B_4H_(10) and B_5H_(11), as small as 0.02 µmole was required for the analysis of the products of a very low conversion kinetic study of the photolysis of diborane. Various analytical methods have been described in the literature for boron hydrides: infrared absorption, neutron absorption, gas chromatography, low temperature fractionation, and mass spectroscopy. Neutron absorption was used to determine total B^(10) content of individual boron hydrides for use in isotopic exchange studies. Gas chromatography was used successfully for B_4H_(10) and B_5H_9, though not for B_5H_(11) because of the latter's instability. Minimum detectable amounts for mixtures were given only for the infrared absorption method, where they were about 0.5 µmole of B_4H_(10) and B_5H_(11), so that the method was too insensitive for much of our investigation. A method was needed where a minimum detectable amount in the presence of large amounts of B_2H_6 was as low as 5 x 10^(-4) mole per cent. It is necessary in certain studies with boron hydrides to proceed to very low per cent conversions to avoid complications due to the reactions of the products.