Protein Molar Concentration Calculator For Chemistry

Protein Concentration Equation:

\[ C = \frac{A_{280}}{\epsilon \times l} \]

Absorbance at 280nm (A₂₈₀):

dimensionless

Molar Extinction Coefficient (ε):

M^-1cm^-1

Path Length (l):

Protein Molar Concentration (C):

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1. What is the Protein Molar Concentration Equation?

The Beer-Lambert law relates the absorption of light to the properties of the material through which the light is traveling. For proteins, absorbance at 280nm (A₂₈₀) is commonly used to estimate concentration based on the protein's molar extinction coefficient.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert equation:

\[ C = \frac{A_{280}}{\epsilon \times l} \]

Where:

\( C \) — Protein molar concentration (mol/L)
\( A_{280} \) — Absorbance at 280nm (dimensionless)
\( \epsilon \) — Molar extinction coefficient (M^-1cm^-1)
\( l \) — Path length (cm)

Explanation: The equation calculates concentration by dividing the measured absorbance by the product of the extinction coefficient and path length.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration determination is essential for biochemical experiments, enzyme kinetics studies, protein purification, and many other laboratory applications.

4. Using the Calculator

Tips: Enter absorbance at 280nm, the protein's molar extinction coefficient, and path length (typically 1cm for standard cuvettes). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How do I find the extinction coefficient for my protein?
A: The extinction coefficient can be calculated from the protein sequence (based on Trp, Tyr, and Cys content) or measured experimentally.

Q2: What if my protein doesn't absorb well at 280nm?
A: For proteins lacking aromatic amino acids, alternative methods like Bradford or BCA assays should be used.

Q3: What is a typical path length?
A: Standard cuvettes have 1cm path length. For microvolume measurements, specialized instruments with shorter path lengths are used.

Q4: How accurate is this method?
A: Accuracy depends on knowing the correct extinction coefficient. It's generally ±10% accurate for pure proteins with known coefficients.

Q5: Can this be used for protein mixtures?
A: For mixtures, the calculated concentration represents total protein based on average extinction coefficient, not individual components.