In regard to spectrophotometric analysis, what is the purpose of the reagent blank?

• A. Correct for interfering chromogens
• B. Correct for lipemia
• C. Correct for protein
• D. Correct for color contribution of the reagents

Answer: (D)

In spectrophotometric analysis, reagents and solvents often have their own color and can absorb light at the measurement wavelength. The reagent blank is prepared with all reagents and solvents in the same concentrations as the test but without the analyte. Its absorbance represents the baseline color contributed by the reagents themselves. By subtracting this background from the sample reading, you remove the reagent-derived color so the final result reflects only the analyte.

That’s why the reagent blank is the best answer: it specifically accounts for the color contribution of the reagents, preventing this background from biasing the measurement. Other interferences like lipemia or protein affect the sample in different ways (turbidity or intrinsic sample absorbance) and are handled separately rather than by the reagent blank.