Science & Lab Tools
Protein Concentration Calculator
Calculate protein concentration and purity using absorbance readings. Get results in mg/mL and μM.
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Related to Protein Concentration Calculator
The Protein Concentration Calculator uses UV spectrophotometry at 280nm (A280) to determine protein concentration based on the Beer-Lambert law. This method utilizes the intrinsic absorbance of aromatic amino acids (primarily tryptophan and tyrosine) at 280nm, making it a non-destructive way to measure protein concentration.
Beer-Lambert Law
The calculation uses the Beer-Lambert law: C = A / (ε × l), where: • C is the protein concentration (M) • A is the absorbance at 280nm • ε is the extinction coefficient (M⁻¹ cm⁻¹) • l is the path length (typically 1 cm)
Concentration Units
The calculator provides results in both mass concentration (mg/mL) and molar concentration (μM). The conversion between these units requires the protein's molecular weight. For common proteins, both the extinction coefficient and molecular weight are pre-loaded for convenience.
The calculator provides comprehensive results to help you understand both the concentration and quality of your protein sample. Understanding these values is crucial for many biochemical applications and experimental planning.
Concentration Values
• mg/mL: Mass concentration, useful for general laboratory work • μM (micromolar): Molar concentration, important for kinetic studies and binding assays Both values are calculated using the extinction coefficient and molecular weight of your protein.
Sample Quality Assessment
• A280 < 0.1: Low concentration, may give unreliable results • A280 0.1-3.0: Optimal range for accurate measurements • A280 > 3.0: Sample too concentrated, dilution recommended
1. Why use absorbance at 280nm?
Proteins absorb UV light at 280nm due to aromatic amino acids (tryptophan, tyrosine, and phenylalanine). This method is non-destructive, meaning your sample can be recovered and used for other experiments. It's also quick and requires minimal sample preparation.
2. What is the extinction coefficient?
The extinction coefficient (ε) is a measure of how strongly a protein absorbs light at 280nm. It depends on the number and type of aromatic amino acids in the protein. For common proteins, these values are well-established and pre-loaded in the calculator. For custom proteins, it can be calculated based on amino acid composition.
3. When should I use the dilution factor?
Use the dilution factor when you've diluted your sample before measurement. For example, if you diluted 1 part sample with 9 parts buffer (1:10 dilution), enter 10 as the dilution factor. This ensures the calculator reports the concentration of your original, undiluted sample.
4. How accurate is this method?
The A280 method is generally accurate to within 5-10% when used properly. Accuracy is best in the absorbance range of 0.1-1.0. Factors that can affect accuracy include: presence of nucleic acids (which also absorb at 280nm), sample turbidity, and very low protein concentrations.
5. What is the scientific source for this calculator?
This calculator is based on the Beer-Lambert law and established principles of protein spectrophotometry. The extinction coefficients and molecular weights are derived from peer-reviewed literature and protein databases such as UniProt and the Protein Data Bank (PDB). The methodology is supported by foundational works in biochemistry, including papers by Edelhoch (1967) in Biochemistry and Pace et al. (1995) in Protein Science, which established the relationship between protein composition and UV absorption. The quality assessment ranges are based on standard laboratory practices documented in Methods in Enzymology and Current Protocols in Protein Science.