Especially when doing low range work, it is important to make sure that your instrument is properly zeroed. Ideally, zeroing should be performed with a certified zero gas. However, mostly since it adds another step to the calibration process, this practice has somewhat fallen out of favor.
The alternative to a zero gas requires that the unit be zeroed in ambient air, in an environment free from the target analyte.
Yet, Industrial Scientific recommends a zero gas in this web posting. And, the “auto-zero” functionality of several BW Technologies by Honeywell gas detectors is dependent on the calibration process being performed—again—in an environment free from the target analyte.
But, what if the ambient air in question is not free of the target analyte? One practice is to employ a “zero filter,” which is some sort of chemical scrubber or adsorbent that will remove the target analyte from the air, before it reaches the instrument’s sensor. Typical zero filters might employ activated charcoal (aka activated carbon), or proprietary agents known to remove certain chemicals.
In certain cases, these chemical scrubbers are provided with an indicating feature, whereby one can determine if the removal power has been used up. Of course, such a feature is not provided with activated charcoal. Thus, one problem with a zero filter would be knowing if it can still remove the target analyte.
A more insidious problem can occur if the zero filter does not remove interferents that might be in the ambient air. Thus, your instrument’s zero is compromised.
While using a zero gas will not eliminate the interference problem, it will—in conjunction with a calibration standard for the target analyte—give you an accurate calibration.