In UV-Vis spectrophotometry for measuring absorbance, what best describes a calibration curve?

• A. A plot of analyte concentration versus path length, used to determine the correct cuvette size for an experiment.
• B. A plot of instrument response (e.g., absorbance) versus known analyte concentration, used to determine the concentration of unknown samples.
• C. A plot of absorbance versus wavelength for a single sample, used to identify the wavelength of maximum absorbance.
• D. A plot of percent transmittance versus time, used to monitor the stability of the light source during measurements.

Answer: (B)

Verified step by step guidance

1. Understand that in UV-Vis spectrophotometry, the goal is to relate the instrument's response to the concentration of the analyte in solution.
2. Recognize that absorbance (A) is directly related to concentration (c) through the Beer-Lambert Law, which is expressed as \(A = \varepsilon \times b \times c\), where \(\varepsilon\) is the molar absorptivity and \(b\) is the path length.
3. A calibration curve is constructed by measuring the absorbance of a series of standard solutions with known concentrations under the same conditions.
4. Plot the measured absorbance values on the y-axis against the known concentrations on the x-axis to create a calibration curve.
5. Use the calibration curve to determine the concentration of unknown samples by measuring their absorbance and finding the corresponding concentration from the curve.