Calculadora de Concentração de Proteína (interpolação linear)
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
C = C₁ + [(C₂−C₁)/(A₂−A₁)] × (A_amostra − A₁)
About this calculator
This calculator linearly interpolates the protein concentration of a sample from two standard points of a calibration curve, such as that obtained in the BCA (bicinchoninic acid) assay. You provide the known concentrations and absorbances of two standards, and the absorbance of the sample. The tool calculates the sample concentration using linear interpolation, assuming a linear relationship between absorbance and concentration within the range of the standards.
The BCA assay is widely used for protein quantification in molecular biology and biochemistry labs. It relies on the reduction of Cu²⁺ to Cu⁺ by proteins in an alkaline medium, followed by reaction with BCA to form a purple complex with maximum absorption at 562 nm. Absorbance is proportional to protein concentration, allowing construction of a standard curve.
To use this calculator, measure the absorbance of two standards with known concentrations (e.g., 0.2 and 1.0 mg/mL) and your sample. Enter the values in the corresponding fields. The result is the interpolated concentration, assuming the sample absorbance lies between the standards. If outside, the tool still calculates, but accuracy is limited.
Cautions: linear interpolation is only valid if the curve is linear in the interval. Always include a blank (zero concentration standard) to calibrate the spectrophotometer. The sample absorbance should fall within the standard range for best accuracy. Avoid saturation (absorbance > 1.5) and dilute the sample if needed.
Frequently asked questions
What if the sample absorbance is higher than the most concentrated standard?
Linear interpolation still works but is less accurate. It is recommended to dilute the sample and repeat the measurement so it falls within the standard range.
Do I need to use exactly two standards?
Yes, the calculator is designed for simple linear interpolation with two points. For curves with more points, use other methods.
Can I use this calculator for methods other than BCA?
Yes, as long as the relationship between absorbance and concentration is linear in the range of the standards. Adjust units as needed.
What is the unit of the resulting concentration?
The unit will be the same as you used for the standards (e.g., mg/mL, μg/mL). Ensure all values are in the same unit.
What is the blank and why is it important?
The blank is a sample without protein (only solvent) that zeros the spectrophotometer. It corrects background absorbance and ensures accurate measurements.