In previous blog posts I’ve talked about calibration types and curve fits. In this installment I’ll cover issues around the calibration zero point. This is a topic that many methods give little guidance on, and various methods can handle it very differently; so it’s easy to be confused over what best practices are, and hopefully I can clear up some confusion.

When I talk about zero points in calibrations, there are two different things to consider. First, whether a zero point or blank needs to be included in the calibration, and second, whether a calibration curve should be forced through zero. I’ll go over how these might affect your calibration before discussing some examples of how various EPA methods handle them.