Two things to consider when using a cadmium coil in a segmented flow analysis system: Pure gas & checking the system for leaks. Pure gas is vital when it comes to the cadmium coil, any impurities in the gas or leaks in the SFA system itself will significantly reduce a cadmium coil’s reductive efficiency.
In segmented flow analysis (SFA) the stream of solutions are segmented with gas. Another very important aspect of cadmium coil handling is the type of gas used for this technique. It is imperative that the gas used is a very pure inert gas, such as nitrogen or helium. Oxygen irreversibly oxidizes the catalytic surface (copper) of the cadmium until it is reactivated again. If the impure gas contains oxygen then the coil will lose its ability to reduce nitrate at a quicker rate then would be normally observed. It may even drop off immediately. This effect will often be characterized by an initial high reduction efficiency, followed by a steady drop in reduction efficiency. Sometimes we see that a very pure gas is used but the gas container, tubing, connections, or cartridges are somehow allowing impure room air to seep into the flow. Once again this will cause a premature loss in reduction efficiency potential for the coil, so it is recommended that the entire system be checked if the problem seems persistent.