If a sample is diluted prior to analysis on a colorimeter or spectrophotometer, should the sample blank also be diluted?
Diluting sample blank
If a sample is diluted prior to analysis on a colorimeter or spectrophotometer, the sample blank should also be diluted. The purpose of the blank is to remove any visual interferences that may be present in the final sample prior to adding reagents (turbidity, color, etc). For this reason, the blank should match the sample prior to adding any reagents.