Molar Extinction Coefficient Formula:
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Definition: The Molar Extinction Coefficient (ε) measures how strongly a chemical species absorbs light at a particular wavelength.
Purpose: It's used in spectroscopy to determine concentrations of substances in solution using Beer-Lambert Law.
The calculator uses the formula:
Where:
Explanation: The slope from a Beer's Law plot (absorbance vs. concentration) divided by the path length gives the molar extinction coefficient.
Details: This value is crucial for quantitative analysis in spectroscopy, as it's a characteristic property of each substance at specific wavelengths.
Tips: Enter the slope from your absorbance vs. concentration plot and the cell path length (default 5.05×10⁻⁸ m for standard 1 cm cells). Path length must be > 0.
Q1: What are typical values for molar extinction coefficients?
A: They vary widely - from 10 to over 100,000 m²/mol depending on the substance and wavelength.
Q2: Why is the path length important?
A: Absorbance is directly proportional to path length, so accurate measurement is essential for correct ε calculation.
Q3: What units should the slope have?
A: The slope should be in absorbance units per molar concentration (AU/M or AU·L/mol).
Q4: Can I use this for any wavelength?
A: ε is wavelength-specific, so calculations must be done for each wavelength of interest.
Q5: How do I get the slope value?
A: Plot absorbance vs. concentration for several standard solutions and determine the slope of the best-fit line.