Phase diagrams

The first pilot batch of protein crystals is produced for detailed and accurate study of the physical-chemical characteristics of this particular crystal form. In a phase diagram study solubility of the crystals is determined with variable parameters. The most common form of phase diagram is two-dimensional; usually it displays soluble protein concentration as a function of one parameter while other parameters are held constant.

The main parameters are temperature, pH and buffer type, precipitant type and precipitant concentration. The presence of additives is also important to study. The additives might have a significant impact on crystal solubility and separation properties. They might change the form of the crystal or improve crystal quality.

Rather complex solubility curves are often seen. These diagrams are important tools for planning of an optimized process. On the basis of phase diagram information, crystallization processes will be controlled and scaled up.