| 摘要 |
A nitrogen gas source, suitable as a field source, comprises a metal air battery having an inlet and outlet to allow a flow of air to pass over its porous cathode. Operation of the battery causes the cathode to remove the oxygen, leaving an oxygen-free gas supply. The output gas may then pass through a chemical filter containing charcoal or molecular sieves to further purify the nitrogen gas. The source is particularly suited for use with an electron capture detector for monitoring tracer substances in air when the cathode is coated with a small amount of stationary phase material of the type used in gas chromatography to minimise absorption of the tracers. The battery is constructed from two identical air cathodes (1) and a single sheet of super purity (99.99 %) aluminium (2) which acts as the positive electrode. Each air cathode (1) is a conducting nickel screen which has a layer of active carbon (3) coated on one side which is exposed to electrolyte. The other side of the cathode is coated with a layer (4) of water-impermeable, gas-porous plastics material and is exposed to a flow of air during operation of the battery. Each air cathode (1) is attached to a plastics sheet (5) using a double-sided adhesive tape (6) which has previously been cut into a grid pattern so as to define an air channel (7). Holes (11) are drilled in each external face of the plastics sheets, interconnecting with the air channels on both sides of the cathode, and fitted with gas inlet (12) and outlet (13) pipes. Air is introduced by means of a small pump. |
