Biomolecule separations are among the most important and most challenging separations because of the varied properties of the different types of biomolecules and the varying properties of the monomer units that comprise the biomolecules. In designing a separation of a biomolecule we must first ask the question of what is the goal of the separation that we are designing. Do we need a large amount of material? How pure do we need the product? Is there a cost constraint on the separation? Is there a time constraint?
More often than not, these are the most important questions that must be answered when we design a separation. Depending on the answers, the final choice for the separation technique may be very different. For instance, we may be working for the analytical division of a genetic engineering company that need to measure the purity of a recombinant protein to report to the FDA. The constraints on our method may be: high degree of accuracy and precision, reasonable time frame for separation (depending on number of samples per day), need for automated method of analysis, limited sample consumption. These constraints seem to indicate that a method like HPLC or CE may be the best method for analysis.
In another part of the company, the pilot plant engineers are working on a method to purify the product for market. The constraints in this department are: large sample volumes, high throughput, low cost, high precision. A bulk scale liquid-liquid extraction technique or a precipitation method may be a much better way to design the separation in this case. In this class, we are going to emulate the scientists in the quality control laboratory. For those interested in process design, an advanced degree in chemical or biotechnical engineering would be appropriate. In either case, the theory behind the separative process is the same: we want to maximize separative processes while minimizing diffusive transport.
In order to design a biomolecule separation, one must first be familiar with the general structure of the molecule: is the molecule a lipid, carbohydrate, protein, DNA? Each class of compounds entails a different set of methods. Sometimes the methods require separations between different classes of biomolecules and sometimes two classes exist in a single mixture or even a single molecule. An example of the latter is the separation of glycosylated proteins.