Protein Purification Techniques
Until the beginning of the 20th century, typical separation technologies included precipitation, filtration, and crystallization.
Since the advent of modern liquid chromatography, it is rare that any one of these early techniques is used alone. Today, a combination of techniques is generally used to assure the quantity, quality, and desired purity of the protein target.
A number of protein precipitation methods are frequently used today. Protein precipitation with a neutral salt, such as ammonium sulfate, is useful for purification and enrichment of a target protein from an extract without loss of activity.
At industrial scale, Cohn’s cold ethanol fractionation/precipitation methods from the 1940s are still used to produce human serum albumin, immunoglobulins, and other blood-based products. However, chromatography methods, in combination with ultrafiltration, have started to replace Cohn fractionation since they offer higher purity and yield, and are easier to automate.
Many biopharmaceuticals are produced using cell culture-based processes that are divided into cell culture, separation, and formulation steps. The separation step is typically divided into two distinct operations—recovery and purification. Recovery operations exploit different filtration technologies extensively to separate product-containing fluids from particulates or can be used to harvest cells prior to lysis.
Combined filtration-centrifugation operations are used for many separation and purification applications at laboratory and industrial scales. Centrifugal ultrafiltration can be used at laboratory scale to concentrate small samples, and at larger scales this combination protects and maintains the performance of expensive chromatography columns and media.
Industrial protein separation usually involves liquid chromatography, and over the decades several chromatographic techniques have been developed. The techniques work by exploiting physical or chemical properties of the target protein and the properties of other substances in the sample solution. Learn about different chromatography techniques here.