For a particular spectrophotometric method the baseline noise of the instrument…
CHEMISTRY · Multi-part · AP · Chemistry · Properties of Substances and Mixtures · Properties of Substances and Mixtures
Problem
For a particular spectrophotometric method the baseline noise of the instrument introduces an absolute absorbance uncertainty of ±0.002, independent of wavelength. A student asserts that performing measurements at the wavelength of maximum absorbance for the analyte minimizes the percentage error in the calculated concentration.
Respond to the following prompts.
(a) Starting from the general relationship between absorbance and solute concentration, show algebraically that the relative (percent) error in concentration is inversely proportional to the molar absorptivity when path length and the absolute absorbance uncertainty are constant.
(b) Explain, without further calculation, how the result in part (a) supports the student’s assertion.
(c) Identify and briefly describe two practical factors—other than analytical sensitivity—that might lead an analyst to choose a wavelength different from the absorption maximum when designing a spectrophotometric method.