Nitrate Contamination: A very real and very well documented effect in various laboratories is the loss of reduction efficiency in cadmium coils caused by nitrate contamination in the ammonium chloride.
Nitrate contamination will cause a steady continuous reaction in a cadmium reduction coil during a run. Depending on the level of contamination, this condition can seriously affect the reduction efficiency of a cadmium coil over time. Often this will be characterized by a color reaction occurring in the solution stream after the color reagent is added but before any samples enter the stream.
Another way of observing this problem is if a change in the baseline occurs after the cadmium coil is placed on the system that has all the reagents online. A good way to test for this problem, as mentioned already, is to look for a color reaction when the cadmium coil is on the system, to watch for an increase in the baseline when the cadmium coil is added online to the reagents, or to simply push some buffer through a cadmium coil into some color reagent and watch for a reaction in the beaker.
If this occurs, the laboratory must find another commercial source for ammonium chloride. Nitrate contamination can happen from other sources, as well, such as water or glassware contamination. It is important to make sure that contamination does not exist anywhere in your laboratory to exclude this as a possible cause for premature loss of cadmium coil reduction efficiency.
