1. What is a Protein Concentration Calculator?

Definition: This calculator estimates protein concentration based on absorbance measurements using the Beer-Lambert law.

Purpose: It helps researchers and laboratory technicians determine protein concentrations in solution for various biochemical applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C \) — Protein concentration (mg/mL)
• \( A \) — Absorbance at 280nm (AU)
• \( \epsilon \) — Extinction coefficient (mL/mg·cm)
• \( l \) — Path length of the cuvette (cm)

Explanation: The absorbance is divided by the product of extinction coefficient and path length to determine concentration.

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration determination is crucial for experimental reproducibility, protein purification, and biochemical assays.

4. Using the Calculator

Tips: Enter the absorbance value (typically at 280nm), extinction coefficient (default 1.0 mL/mg·cm), and path length (default 1.0 cm). Extinction coefficient and path length must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is the extinction coefficient?
A: The extinction coefficient is a measure of how strongly a protein absorbs light at a specific wavelength, typically 280nm for proteins.

Q2: How do I find the extinction coefficient for my protein?
A: It can be calculated from the protein sequence or measured experimentally. Many online tools can predict it from amino acid composition.

Q3: What if my cuvette has a different path length?
A: Adjust the path length value accordingly (standard cuvettes are 1cm, but micro-volume cuvettes may have shorter path lengths).

Q4: What wavelength should I use for measurement?
A: Proteins are typically measured at 280nm where tryptophan and tyrosine residues absorb strongly.

Q5: Does this work for all proteins?
A: This method works best for purified proteins. For complex mixtures, other methods like Bradford assay may be more appropriate.