= 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.<Blank correction in the IUPAC Gold Book>[08008, definition and note1]{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, then
$$
\operatorname{Var}(X-\overline B)=\operatorname{Var}(X)+\frac{\operatorname{Var}(B_i)}{n}.
$$
With sample <variance>4, single-blank <variance>9 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 $-\log_{10}(0.8)\approx0.09691$. Subtracting0.5 from0.4 would represent a different operation.<Blank correction in the IUPAC Gold Book>[08008, note2, subtraction and transmittance division]{ref} These examples show why specifying the blank material alone does not specify a valid <blank correction>.
Back to article page
