How is total protein in a sample typically measured?

How is total protein in a sample typically measured?

• A. Using a spectrophotometer
• B. Using a refractometer
• C. Using a hemocytometer
• D. Using a centrifuge

Answer: (A)

Total protein is quantified by converting protein to a colored complex using a dye-based assay, then measuring the color’s intensity with a spectrophotometer. The dye binds to protein, and more protein yields more dye binding, producing a stronger color. The spectrophotometer reads this color at a specific wavelength, giving an absorbance value that is proportional to protein concentration. By running standards with known protein amounts, you create a calibration curve, and the sample’s absorbance is translated into its protein concentration. This method is preferred because it is sensitive, adaptable to many sample types, and provides a direct quantitative readout. A refractometer measures refractive index and is used only for estimating total solids or protein indirectly in some foods, not for precise total protein concentration. A hemocytometer counts cells. A centrifuge separates components but does not quantify protein by itself.

Total protein is quantified by converting protein to a colored complex using a dye-based assay, then measuring the color’s intensity with a spectrophotometer. The dye binds to protein, and more protein yields more dye binding, producing a stronger color. The spectrophotometer reads this color at a specific wavelength, giving an absorbance value that is proportional to protein concentration. By running standards with known protein amounts, you create a calibration curve, and the sample’s absorbance is translated into its protein concentration. This method is preferred because it is sensitive, adaptable to many sample types, and provides a direct quantitative readout. A refractometer measures refractive index and is used only for estimating total solids or protein indirectly in some foods, not for precise total protein concentration. A hemocytometer counts cells. A centrifuge separates components but does not quantify protein by itself.