In the field of gas detection, an “interference” is an unwanted response on your instrument, caused by some chemical other than the target analyte. Generally speaking, no analytical method—using any technology—is completely specific. Thus, it is important for instrument manufacturers to document these interferences to the best of their ability.
Here at Interscan, we provide interference data on a series of charts. Still, this topic is not well understood, so we offer some key points:
1. Owing to the nature of electrochemical voltametric sensors, which can operate in either an oxidative or reductive mode, interferences can be positive or negative. This is so indicated on our interference charts.
2. Since the sensor for the target analyte is not characterized for ideal performance with the interferent, you cannot assume that the interferent would show linear or reproducible performance on the sensor. Thus, you cannot use this sensor as if it were optimized for the interferent. In other words, if you are seeking to accurately detect the interferent, find an appropriate analyzer for this task.
3. Interference data is provided only for compounds common to environments involving the target analyte. Such data may also be limited to the availability of standards to generate suitable concentrations of the interferent. If you are concerned about a potential interferent that is not shown on our charts, please contact us.
4. Despite best efforts of the instrument manufacturer and the customer, it is possible that some previously unknown interferent may exist in your environment. This might even occur after all reasonable applications engineering is done, only to appear as “bizarre” readings on the newly installed gas analyzer.
Sometimes such unexpected readings may be completely legitimate, and can be confirmed by alternative methods of analysis. In other cases, reconsideration of the monitored environment will be in order. This could include further elucidation of all nearby chemical processes, and a comprehensive air analysis of the area in question.
5. Given all the above, it is important to avoid becoming obsessed with potential interferents, to the point that it clouds your judgment. We are reminded of a case years ago when hospitals were just beginning to get serious about monitoring ethylene oxide. A prestigious institution in New York City was in the process of replacing an old semiconductor sensor based monitoring system, which was constantly false-alarming, since the sensor responded to essentially all organic compounds.
The supervisor gave us a list of more than 300 compounds, which “could be present” in the hospital—well beyond what could conceivably exist in the sterile processing department. He demanded that we (and other prospective vendors) furnish data on how our sensor would respond to all of these chemicals. Sadly, this ended up being nothing more than a tactic to avoid buying any ethylene oxide monitoring system. We heard that the SPD was without monitoring instrumentation for around three years before cooler heads prevailed.