Abstract
Here we explored the conditions for synthesizing [^13^N]N~2~ in a state that is suitable for the administration to plant root nodules enabling studies of nitrogen fixation. [^13^N]N~2~ was prepared batchwise, starting with [^13^N]NO from the ^16^O(p,Ξ±)^13^N nuclear reaction on a liquid water target. [^13^N]NO was first reduced to [^13^N]NH~3~ using Devarda's alloy, and then the [^13^N]NH~3~ was oxidized to [^13^N]N~2~ by hypobromite using carrierβadded NH~4~Cl. The amounts of carrier NH~4~Cl and hypobromite were varied to determine the effects these parameters had on the radiochemical yield, and on the radiotracer specific activity. As expected, increasing the amount of carrier NH~4~Cl improved the radiochemical yield. Unexpectedly, increasing the amount of excess hypobromite from 1.6βfold to 6βfold molar equivalents (relative to NH~4~Cl) improved the radiochemical yield and radiotracer specific activity under all conditions of carrier NH~4~Cl. As a comparison, we measured [^13^N]N~2~ specific activity derived from inβtarget production based on a 50βΒ΅Aβmin irradiation driving the ^14^N(p,pn)^13^N reaction on a gaseous N~2~ target. The βwetβ radiochemistry approach afforded two advantages over the inβtarget approach with a βΌ600βfold improvement in specific activity, and the ability to collect the tracer in a small volume of gas (βΌ20βmL at STP). Copyright Β© 2010 John Wiley & Sons, Ltd.