21. The calibration curve for the determination of nitrate (NO3⁻) in agricultural runoff water using UV-visible spectrophotometry was found to be
A = 0.025 × [NO3⁻] + 0.080
where A is the absorbance measured at 220 nm and the nitrate concentration is expressed in μM. The reagent blank produced an absorbance of 0.060 ± 0.010. Which of the following statements is INCORRECT?
(A) According to the Beer-Lambert law, increasing the optical path length of the cuvette enhances absorbance sensitivity for a given analyte concentration.
(B) 0.080 represents the background absorbance arising from the reagent blank and the sample matrix.
(C) The coefficient of determination (R²) can be greater than 1 when the calibration data show excellent linearity.
(D) The relative standard deviation of the reagent blank measurement is 16.7%.
(E) The limit of detection (LOD; signal to noise = 3) estimated from the blank standard deviation is 1.2 μM.