UnusualAn introduction to the notion of interferences (those other gases in the environment that might respond in your instrument, thus “interfering” with your measurement of the target analyte), is given here. We continue the discussion on interferences by considering what can be done when you are confronted with an interference that is “unusual,” that is, it does not appear on any available documentation from the instrument or sensor manufacturer.

An interference can be undocumented if it does not typically occur in the most common applications whereby a particular toxic gas in found. Indeed, “common” interferents are usually the ones most asked about when a gas sensor or instrument line for a certain gas is first introduced.

So, what should you do if you suspect that an unusual interference might be present in your application? In most cases, before inquiries are made with a manufacturer of toxic gas detection instruments, background measurements are performed in your environment, most often using wet chemical techniques. It is usually this initial air analysis that becomes the basis for your inquiry to an instrument manufacturer.

Thus, you would inquire with the instrument vendor: “I need to monitor [the target analyte]. at a range of 0-“X” ppm (or ppb). Also present are {name the interferences, and their expected concentrations].” If one or more of these interferents are “unusual,” you would be so informed right away. Specific testing will have to be performed, and there will likely be a charge for this service, unless the instrument manufacturer feels that the information requested may be of interest to others, or if your application includes enough measuring points to justify the cost.

Given the testing results, you may decide to search for an instrument using a different analytical principle of operation that promises no such interference (although that would have to be proven). It may also be possible to employ the original instrument method, and use a special algorithm to correct for the interference.

In this, and so many other cases, good applications engineering is essential for a successful gas detection project.

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