How is total protein in a sample typically measured?

Total protein in a sample is typically measured using a spectrophotometer, which analyzes the absorbance of light at specific wavelengths by the proteins present in the sample. This method is based on the principle that proteins will absorb light, and the amount of light absorbed correlates with the concentration of protein.

When using a spectrophotometer, a common method for total protein measurement is the Biuret method, where proteins form a complex with copper ions in an alkaline solution. The intensity of the resulting color change is measured spectrophotometrically and is directly proportional to the protein concentration.

The refractometer, mentioned in the response, is primarily used to measure the refractive index of a liquid, which can provide indirect information about protein concentration in some cases (such as in urine). However, it is not the standard method for measuring total protein concentration in serum or plasma samples.

The hemocytometer is a device used for counting cells in a sample and is not applicable for measuring total protein levels. A centrifuge, on the other hand, is used for separating components of a sample based on density but does not measure protein concentration directly.

Thus, while the refractometer can be useful in specific scenarios, using a spectrophotometer is