If you have pure proteins in solution, you can use any of several protein assay kits that are commercially available (examples, BCA assay and Bradford assay). Each one requires a standard. The standard, in these cases, can be the same protein that you are measuring, since they can be purchased.

If the pure proteins are in a solution in which there is nothing else that absorbs in the far UV, you can use the method of Gill and von Hippel to calculate the molar extinction coefficient (or look it up somewhere), and measure the UV absorbance to get the concentration. This method requires a solution of 8 M guanidine-HCl to fully denature the protein.

Gill, S.C. and von Hippel, P.H. (1989). Calculation of protein extinction coefficients from amino acid sequence data. Anal. Biochem. 182:319-26

The refractive index of the solution of pure proteins can be used to measure the concentration of the protein, using the refractive index increment (dn/dc) for globular proteins (0.185 mL·g−1), if a refractometer is available.

For pure proteins, you can send them to a specialist lab to measure the concentrations by amino acid analysis.

If the proteins are present in mixtures, then you can use an ELISA kit with specificity to the protein of interest. These can be purchased, but are expensive. Standards of the same proteins of known concentration are required, and should be supplied with the kit.

If the protein of interest is a major component in a mixture, a semi-quantitative method would be to use SDS-PAGE, Coomassie Blue staining, and densitometry to measure the percentage of stain in the band corresponding to the protein of interest, and compare that to the total protein concentration measured by some other method, such as Bradford or BCA. This requires a densitometer or gel imager with this capability.

There are a variety of other possibilities, depending on the nature of the sample, the availability of a standard of comparison, and the available equipment.

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These products include total protein assay kits and reagents, such as Bradford assay reagents, BCA assay kits, bovine serum albumin (BSA) standards, and other spectrophotometer and microplate protein assay products used to precisely determine and measure total protein concentration following cell lysis, labeling or purification and you can many mothed for determination albumin it is easy method kit spectrophotometry

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Bradford Assay: The Bradford assay is a colorimetric protein assay based on the binding of Coomassie Brilliant Blue dye to proteins. The intensity of the dye-protein complex is directly proportional to the protein concentration. This assay is relatively quick and simple and can be used to quantify both albumin and casein.