What blank is used to correct absorbance due to reagent color?

• A. Reagent blank
• B. Sample blank
• C. Instrument blank
• D. Reference blank

Answer: (A)

In spectrophotometry, the color of reagents can contribute to the measured absorbance, not just the analyte. To isolate the true signal from the sample, you measure a blank that contains all reagents except the analyte—the reagent blank—and use it to correct the reading. This background absorbance is subtracted from the sample’s absorbance, giving the true absorbance due to the analyte alone. The instrument blank accounts for the instrument’s baseline (usually with solvent only), and a sample blank would correct for components in the sample matrix, but not specifically for reagent color.