Liquid Chromatography at the Industrial Scale

There is a growing demand for high purity chemicals within the technical, life science and fine chemical industries. As new synthetic routes are discovered and purity requirements increase, the demand for more sophisticated processing techniques is more prevalent than ever before.

Companies selling into industries with a strong emphasis on quality – such as pharmaceuticals, semiconductors, agrochemicals and medical devices – have specifications and purity requirements that are often set by the purchasing entity. External specifications can be difficult to meet and, at times, require advanced purification methods like chromatography, particularly when alternatives such as distillation, recrystallization and solvent-to-solvent extraction do not work.

Chromatography is based on the principle “like attracts like”. The more similar two materials are in polarity and structure, the stronger the intermolecular attractive forces are between them, which enables the separation of large quantities of compounds based on minor differences in molecular structure. Although chromatography is more commonly known for its analytical applications, it can also be a powerful tool for removing impurities from large scale processes.

Liquid chromatography

In liquid chromatography, a system consists of a column filled with stationary (or solid) phase, mobile phase(s), detection instrument(s) and pump(s) to move a mixture through a system that separates solutes.

The mobile phase flows through the stationary phase, carrying solutes that remain in the column for varying lengths of time, due to differences in molecular structure and varying strengths of intermolecular interactions. The interactions between solutes and column packing material (solid phase) allow one specific component, or multiple components, to exit the column at different times. Varying retention times allow for the collection of purified materials once an elution profile has been identified.

Several varieties of liquid chromatography exist – including normal phase, reverse phase and ion exchange – that are dependent on the relative polarities of mobile phases, stationary phases or ionic strength of solutions. Normal phase media, such as silica and alumina, is typically used for one purification and then disposed of (because of chemisorption), while reverse phase and ion exchange resins can be regenerated and reused for many cycles.

Separating power

Liquid chromatography can be seen at almost any stage of a process, from generating sub gram amounts to producing thousands of tons of purified material. During industrial synthesis, byproducts often have structures very similar to the target material, making them difficult to separate with techniques such as solvent extractions or recrystallization. Extractions from biological sources also suffer from challenging purifications, due to the variety of molecules that can be coextracted from a living organism.

Most commercially available chemical and drug products require a high degree of purity which, in turn, drives the need for effective separation techniques. Among the manufacturing techniques available, chromatography is often the most sensitive purification method due to its exceptional separating power. Structural changes in a molecule can alter its polarity, hydrogen bonding or charge, influencing the intermolecular interactions between solutes and the stationary phase. Differentiating factors can be as subtle as changing a single atom or even one bond. In contrast, distillation is limited to volatile compounds, while recrystallization and solvent-to-solvent extractions are typically used for mixtures with significant differences in polarity, charge, hydrogen bonding or solubility.

The specific interaction between solutes and solid phase is dependent on a variety of factors, including column packing material, mobile phase (or mixture of mobile phases), flow rate and sometimes temperature. Numerous variables can be adjusted to meet the separation needs of crude mixtures that are difficult to separate, allowing for flexibility and customization.

Chromatography supports further specialization and continuous development due to its versatility in modification. Recent advancements have improved specificity with the introduction of specialty solid-phase materials, supercritical solvents and simulated moving beds.

Suppliers

The type of column packing materials used in liquid chromatography can drastically impact how solutes elute and can be customized with regards to composition, polarity, charge, particle size, surface area, pore diameter, pore volume, pH and more.

The ability to customize solid phase materials, mobile phases and process conditions ensures chromatography systems can be optimized for maximum yield, purity and efficiency. Experienced suppliers can add significant value to a chromatography process by offering customizations and higher quality materials that directly enhance the performance of the separation media. In addition, suppliers with experience in chromatography applications can provide essential supporting quality documentation to ensure compliance with domestic and international regulatory requirements.

Diverse applications

Chromatography’s versatility as a purification technique allows it to be used in a variety of large-scale processes, including:  

• Phospholipids: One of the largest applications of industrial chromatography, phospholipid purifications separate by utilizing the dynamic environment in which lipids can exist.
• Peptides: In the development of smaller peptide-based pharmaceuticals (e.g., immunosuppressants), chromatography plays a critical role with separations that require a high degree of specificity and can distinguish between complex molecules.
• Antibiotics: A wide variety of antibiotics have been, and continue to be, purified at the industrial scale using liquid chromatography. Synthetically produced antibiotics and extracted antibiotics can be difficult to purify due to the byproducts generated from a reaction and the substances that are coextracted as impurities.
• Inhibitor removal: By effectively removing inhibitor and moisture from monomers prior to the polymerization process, liquid chromatography leads to higher-quality polymer products.
• Small Molecules: By utilizing materials such as silica gel or alumina, which have a high surface area, small molecules can be purified at one or multiple stages of a production process. These materials, along with the organic solvents used as mobile phases, are generally low-cost at the commercial scale, helping to reduce overall expenses.
• Biological Molecules: Products like monoclonal antibodies have broadly adopted chromatography as one of the purification steps in production and occupy one of the largest markets for development of new solid phase materials.

Economics at the industrial scale

Using liquid chromatography for a commercial scale process can sometimes be perceived as costly. As is common in many other areas, such as semiconductors or processes that require a precious metal catalyst, raw materials and manufacturing methods can significantly impact overall expenses.

While it may not always be the first choice for purification, chromatography is often the only technique capable of achieving the high purity requirements of modern-day technologies. Consequently, companies need to ensure the value of the final product outweighs the manufacturing expenses before implementation. Ultimately, whether chromatography – or any other techniques that add value to a product – can be effectively covered depends on what the market will bear. In the pharmaceutical industry, especially in biologics, products can sell for well over $10,000 per gram, allowing ample margin to cover a liquid chromatography purification step.

During the production of monoclonal antibodies, ion exchange medias are often used and can sell for more than $500 per kilogram, even at the commercial scale. Fortunately, the value of the final active ingredient is several orders of magnitude higher. Most ion exchange resins can be regenerated and reused, to reduce the cost of manufacturing and to help maintain healthy profit margins.

Although the costs of chromatography should be considered during scale up, products do not need to sell for tens of thousands of dollars per gram to make it feasible. Many chemical products, priced well below $20 per kilogram, utilize chromatography for purification. Normal phase media is frequently employed in industrial-scale processes where cost reduction is essential, despite the stationary phase often being single-use. The high volume of solid and mobile phase materials required allows for bulk purchasing at lower prices compared to ion exchange or reverse phase.

In large-scale chromatography, customers often pay under $10 per kilogram for silica gel or alumina packing media, which can generate a finished product with greater than 99% purity. Spent media can be sold to other industries, like cement manufacturing, to further reduce costs and waste.

Another key area that can have a major impact on operating expenses in an industrial-scale chromatography process is the column packing step. Although prepacked or disposable columns can seem appealing because they circumvent the need for column packing resources, it does not take long for a reusable column to pay for itself.

Managing the column packing process internally not only supports leaner manufacturing, it is also the only viable option for larger chromatography skids, as prepacked or disposable columns are not available past a certain size. Instead of purchasing a new column when the media loses efficiency, the solid phase inside the column can be replaced, with expenditures limited to the value of the stationary phase and the solvents used during packing. 

Conclusion

By consistently creating extremely high levels of purity, advanced purification processes can open the door to new materials and technologies. Separating power, flexibility, customization and repeatability are the features of liquid chromatography that allow for efficient separation of challenging mixtures, succeeding where other techniques fall short. With an established history in industrial scale manufacturing across a wide range of applications, the value chromatography brings as a purification tool is undeniable.