Protein standardization II: Dry mass determination procedure for the determination of the dry mass of a pure protein preparation.

A procedure has been developed for the determination of the dry mass of a pure protein preparation dissolved in one electrolyte. The procedure not only renders the concentration (in g/l), but additionally gives the partial specific volume of the protein (in ml/g). The latter is an important parameter for the characterization of a specific protein. Furthermore, the importance of extensive dialysis against one electrolyte is discussed. For the drying of human serum proteins it is clearly shown that KCl is preferred to NaCl due to its stable temperature curve. By observing the parallel fluctuations in the weight of the empty vials during drying, an average correction factor is introduced, which greatly minimizes these changes. The assay principle is discussed from a mathematical as well as from a practical point of view. A detailed procedure is described and the final results for three primary pure proteins (prealbumin, orosomucoid and transferrin) are presented. Finally, important parameters such as the wavelength of maximum absorbance, the absorption coefficient and the specific refractive increment are discussed and values for the three proteins are presented. When these parameters have been established the future determination of concentration and the characterization of pure protein solutions are greatly facilitated. These procedures were important tools for ascribing mass values for prealbumin, orosomucoid and transferrin to the international reference preparation CRM 470.