Although supercritical fluids were used as eluents for chromatographic separations in 1962, the term supercritical fluid chromatography (SFC) was first used only five years later. Since then, the technique has come a long way, particularly in the pharmaceutical industry. SFC has rightfully earned its place in the pharmaceutical industry simply because it has outperformed other techniques used in the field.

Basic needs of the pharmaceutical industry

The basic requirements of clinical laboratory/pharmaceutical field for chromatography are as follows:

• Minimum requirements of sample and sample preparation
• High sensitivity, specificity, reproducibility, and throughput
• Quantitative and accurate
• Automated, rapid, and easy-to-operate instrumentation
• Simple and easy to use on a daily basis
• Economical
• Easy interpretation of results

Use of SFC in terms of pharmaceutical requirements

Analytical chemists continuously look for processes, techniques, materials, and instrumentation that can help them with any of the above features. One technique that has made steady advances in all these areas is SFC.

The low viscosity and high diffusivity of a supercritical fluid make it an excellent choice as a chromatographic mobile phase, as this ensures rapid separation and high efficiency.

Use of supercritical fluids, particularly carbon dioxide, results in a tremendous reduction in the use of organic solvents, which has cost, health, and safety benefits. All these make SFC an effective alternative to HPLC (High-Performance Liquid Chromatography) for many separation processes in the industry.

Changing the pressure and temperature parameters in SFC requires detector systems that are compatible with the parameters of the separation process. Detectors in SFC have also come a long way in SFC: UV-visible detection, differential refractometry detection, heat-of-adsorption detection, fluorometric detection, thermionic (nitrogen–phosphorus) and Fourier transform infrared (FT-IR) detection, flame-photometric and ion mobility detection, electrochemical detection, and supersonic jet spectroscopy detection are all possible with SFC.

The first commercial introduction of SFC in 1982 was followed up a decade later by the introduction of second-generation hardware for high efficiency packed columns, with independent flow control under varied pressure and composition gradient conditions. All these made the rapid adoption of SFC in the pharmaceutical industry possible, as using the appropriate column plays a key role in the separation processes of individual compounds.

Safety aspects and the need for chiral separations in the pharmaceutical industry

Clinical research laboratories have two main goals:

• Identification of molecules in body fluids (blood, urine, cerebrospinal fluid) or tissues that (1) are toxic, (2) indicate a predisposition to disease, or (3) have therapeutic efficacy—any of which may serve as a marker.
• Development of drugs that is safe and effective for specific disease conditions.

In both, the absolute purity of the molecule of interest is of primary importance; undetected impurities may lead to lesser efficacies or toxic side effects. Biomolecules are chiral, and living systems are known to have preferences for specific enantiomers for almost every molecule. The absorption, metabolism, and excretion of enantiomers are also known to be quite different in living systems. For these reasons, the FDA (Food and Drug Administration) in the United States and the CHMP (Committee for Medicinal Products for Human Use) in the European Union have issued guidelines for pharmaceutical drug use—that only therapeutically effective enantiomers of chiral drugs can be released into the market.

Chirality in living systems implies that every enantiomer of a drug should be studied fully regarding its metabolism as well as its pharmaceutical properties before an enantiomer can be claimed to be of therapeutic use. This, in turn, depends on powerful methods of chiral detection and separation.

SFC has been the single most important technique used in the pharmaceutical industry for the detection, separation, and purification of chiral molecules. It has been an effective alternative to HPLC in chiral separations because of its high speed, shorter analysis time, limited environmental impact, and higher efficiency.

Areas served by SFC in the pharmaceutical industry

SFC has met the chromatography needs of the pharmaceutical industry by providing efficient and selective testing capabilities on the analytical, semi-preparative, and preparative scale.

It has been helpful in all stages of pharmaceutical drug preparation:

• Chiral separation of the enantiomers of a molecule
• Purification of each of the enantiomers in sufficient quantities to permit a study of the enantiomer’s pharmacokinetic and metabolic properties
• Identification of the enantiomer of choice as a possible therapeutic agent
• Purification on higher (production) scales

The introduction of preparative scale packed columns for SFC in 2007 and ultra-fast SFC in 2008 have helped SFC take great strides in chiral separations as well as drug discovery and development.

SFC now occupies a niche in the discovery and development of a wide variety of drugs such as antibiotics, steroids, non-steroidal anti-inflammatory drugs, barbiturates, and prostaglandins.

As the supercritical fluid mobile phase releases, no additional carbon dioxide to the atmosphere, it helps the industry in meeting green analytical chemistry standards, which is why it is called as the “green technique.”

Further Reading

• All Chromatography Content
• Chromatography Overview
• Gas Chromatography-Mass Spectrometry (GC-MS) Applications
• High Performance Liquid Chromatography (HPLC)
• Liquid Chromatography-Mass Spectrometry (LC-MS) Applications