Cohnfractionatie

Cohnfractionatie, or Cohn fractionation, is a method for separating plasma proteins by ethanol-induced precipitation at low temperatures. Developed by Edwin J. Cohn in the 1940s, the process enabled large-scale fractionation of human plasma to obtain multiple plasma-derived proteins. It played a pivotal role in the early production of clinical products such as albumin, immunoglobulins, and coagulation factors.

The technique involves cooling plasma and gradually adding ethanol to produce selective precipitation of different protein groups. By carefully adjusting ethanol concentration, pH, and ionic strength, fractions are precipitated in sequence and collected as Fraction I, Fraction II, Fraction III, Fraction IV, and Fraction V. Temperature is typically maintained in the range of 0 to 5 degrees Celsius to favor specific precipitations. Each step is designed to enrich for particular classes of proteins while leaving others in solution for later processing.

In practice, the fractions are described by their protein content rather than exact compositions. Fraction V is generally enriched in albumin, while combined fractions such as II+III are associated with immunoglobulins; other fractions contain fibrinogen and various coagulation factors. The original scheme allowed a single starting material (plasma) to yield multiple therapeutic protein products.

Historically, Cohn fractionation informed the development of plasma-derived therapeutics and established foundational principles for protein purification. Its influence extended to process design, quality control, and safety standards in biopharmaceutical manufacturing. In modern practice, the traditional ethanol-based fractionation has been complemented or replaced by chromatographic techniques and robust virus inactivation steps, though the conceptual framework of sequential precipitation remains relevant in protein purification and process development.