1. What is Molar Absorptivity?

Molar absorptivity (ε) is a measure of how strongly a chemical species absorbs light at a particular wavelength. It is a fundamental parameter in the Beer-Lambert law and is characteristic of each substance at a specific wavelength.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert law relationship:

Where:

• \( \varepsilon \) — Molar absorptivity (L/mol·cm)
• \( \text{Slope} \) — Slope from absorbance vs concentration plot (L/mol)
• \( \text{Path Length} \) — Length of the light path through the sample (cm)

Explanation: From the Beer-Lambert law (A = εcl), plotting absorbance (A) vs concentration (c) gives a straight line with slope = εl, where l is the path length.

3. Importance of Molar Absorptivity

Details: Molar absorptivity is crucial for quantitative analysis in spectroscopy, determining unknown concentrations, identifying substances, and validating analytical methods.

4. Using the Calculator

Tips: Enter the slope obtained from your absorbance vs concentration calibration plot and the path length of your cuvette or sample cell. Both values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What is the Beer-Lambert law?
A: The Beer-Lambert law states that absorbance (A) is directly proportional to concentration (c) and path length (l): A = εcl, where ε is the molar absorptivity.

Q2: How do I obtain the slope for this calculation?
A: Measure absorbance at different concentrations, plot absorbance vs concentration, and determine the slope of the best-fit line through the data points.

Q3: What are typical values for molar absorptivity?
A: Values range from near zero for weak absorbers to over 100,000 L/mol·cm for strong absorbers. Most organic compounds have ε values between 1,000-50,000 L/mol·cm.

Q4: Does molar absorptivity depend on wavelength?
A: Yes, molar absorptivity is wavelength-dependent and is usually reported at the wavelength of maximum absorption (λmax).

Q5: What factors affect molar absorptivity measurements?
A: Temperature, solvent, pH, and instrumental factors can affect measured values. Always use consistent conditions for accurate comparisons.