 Blank correction

Blank correction removes the modeled effect of a blank indication from a measured response. The analytical blank supplies evidence about a background contribution; the measurement model specifies how to correct for it. The quantities combined must be of the same kind.^[ref]

For an additive example, a sample response of12 units and mean blank response of2 units give a corrected response of10 units. The correction retains measurement uncertainty. If sample response $X$ is independent of the mean of $n$ independent blank measurements, thenWith sample variance4, single-blank variance9 and $n=9$, the corrected variance is5, not zero. Dependence requires the corresponding covariance term in the propagation.

A different measurement model can require division. Invented transmittance indications0.4 for the sample and0.5 for the blank give corrected transmittance $0.4/0.5=0.8$. The associated absorbance is $-{\log }_{10}(0.8)\approx 0.09691$. Subtracting0.5 from0.4 would represent a different operation.^[ref] These examples show why specifying the blank material alone does not specify a valid blank correction.