Producing and dispensing small quantities of 15N2 gas at atmospheric pressure.

Heavy nitrogen (N2) 1 is often used as a label for nitrogen Wxation experiments in which it is desirable to monitor directly the rate of nitrogen Wxation and the destination of the resulting metabolites in an organism or ecosystem [1–4]. Heavy nitrogen can be purchased in a pressurized cylinder or produced in the laboratory with specialized equipment, but both methods of obtaining the gas are expensive. These methods also introduce a complication because a typical nitrogen Wxation experiment requires samples of gas at atmospheric pressure. The pressure must be reduced with a pressure regulator in the case of gas in a pressurized cylinder, and traditional laboratory methods produce heavy nitrogen at pressures well below atmospheric that are not generally suitable for direct use in nitrogen Wxation experiments [1]. This is because there is no easy way in which to compress the gas to atmospheric pressure for subsequent injection into a sample bottle. This report describes a simple alternative technique that produces small quantities (limited by the volume of available plastic syringes) of heavy nitrogen at atmospheric pressure with readily available analytical chemicals, laboratory supplies, and equipment. The technique is based on that of Wood and Kennedy [4] but does not require their special apparatus. The technique produces heavy nitrogen through the reaction of N-labeled ammonium sulfate [(NH4)2SO4] with lithium hypobromite (LiOBr), and the gas subsequently is sparged Wrst with acidiWed potassium permanganate (KMnO4) and then with acidiWed water to remove contaminating oxides that otherwise would be taken up by