Protein Concentration Calculator Extinction Coefficient

Beer-Lambert Law:

\[ \text{Conc (mg/mL)} = \frac{\text{Abs}}{\varepsilon \times \text{path}} \]

Protein Concentration:

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1. What is the Beer-Lambert Law?

The Beer-Lambert law describes the relationship between absorbance and concentration of a substance in solution. It states that absorbance is directly proportional to the concentration of the absorbing species and the path length through which light travels.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert law equation:

\[ \text{Conc (mg/mL)} = \frac{\text{Abs}}{\varepsilon \times \text{path}} \]

Where:

\( \text{Conc} \) — Protein concentration (mg/mL)
\( \text{Abs} \) — Absorbance at specific wavelength (AU)
\( \varepsilon \) — Extinction coefficient (mL/(mg·cm))
\( \text{path} \) — Path length of cuvette (cm)

Explanation: The equation calculates protein concentration based on the measured absorbance, the protein's specific extinction coefficient, and the path length of the measurement cell.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration determination is essential for various biochemical applications including enzyme kinetics, protein purification, quantitative Western blotting, and ensuring consistent experimental conditions.

4. Using the Calculator

Tips: Enter absorbance value (typically at 280nm for proteins), the extinction coefficient specific to your protein, and the path length of your cuvette (usually 1.0 cm). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical extinction coefficient for proteins?
A: Extinction coefficients vary by protein. Common values range from 0.5-2.0 mL/(mg·cm) at 280nm. The coefficient can be calculated from the protein's amino acid composition.

Q2: Why measure at 280nm?
A: Proteins absorb light at 280nm due to tryptophan and tyrosine residues. This provides a convenient method for protein quantification without additional reagents.

Q3: What if my cuvette has a different path length?
A: The standard path length is 1.0 cm. If using a different path length, enter the actual measurement. Many micro-volume cuvettes have path lengths less than 1.0 cm.

Q4: Are there limitations to this method?
A: The method assumes the sample is pure protein. Nucleic acid contamination or turbidity can interfere with accurate measurements. Always blank with appropriate buffer.

Q5: How do I determine the extinction coefficient for my protein?
A: The extinction coefficient can be calculated from the protein's amino acid sequence using online tools or measured experimentally using quantitative amino acid analysis.