When performing a titanium dioxide assay using a NIST standard that is 99.59% pure, do you add the purity to the calculation?

For example:

(Vol KMnO4 titrant)(equivalency factor)(Normality of KMnO4)(100)

/(weight sample)(purity)

I was told that the purity is not used b/c we are titrating for the assay value. But in LC/GC analysis, the purity of spl and std are entered into assay calculations. It seems to me that entering the known purity would normalize the calculation, since you know you did not start with 100% pure titantium dioxide.

Please advise!!