1. What is a Protein Concentration Calculator?

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

Purpose: It helps researchers and laboratory technicians determine protein concentrations in solution using spectrophotometric data.

2. How Does the Calculator Work?

The calculator uses the Beer-Lambert law:

Where:

• \( C \) — Protein concentration (mol/L)
• \( A \) — Absorbance (unitless)
• \( \epsilon \) — Molar absorptivity (L/mol·cm)
• \( l \) — Path length (cm)

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

3. Importance of Protein Concentration Measurement

Details: Accurate protein concentration determination is crucial for experiments, protein purification, enzyme kinetics studies, and biochemical assays.

4. Using the Calculator

Tips: Enter the absorbance value, molar absorptivity (specific to your protein), and path length (default 1.0 cm). Absorbance must be ≥ 0, while ε and l must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is molar absorptivity?
A: Molar absorptivity (ε) is a measure of how strongly a chemical species absorbs light at a given wavelength, characteristic for each protein.

Q2: What's a typical path length?
A: Most spectrophotometer cuvettes have a 1.0 cm path length, but some micro-volume instruments use shorter paths (e.g., 0.1 cm).

Q3: How do I find the molar absorptivity for my protein?
A: Check literature values for your specific protein or measure it using known concentrations.

Q4: What wavelength should I use for measurements?
A: Typically 280 nm for proteins (tryptophan/tyrosine absorbance), but some assays use other wavelengths.

Q5: Why might my calculated concentration be inaccurate?
A: Possible reasons include incorrect ε value, light scattering, interfering substances, or absorbance outside the linear range.