Supercritic​al Fluid Chromatography (SFC) evolved from the work of scientists exploring the unique properties of fluids at or above their critical point. SFC as an analytical technique, however, began use in the 1960s, when its potential for efficient separations was realized.

SFC has seen significant advancements in technology, understanding, and applications over the years. Technological innovations, such as the development of high-pressure delivery pumps and pressure vessels, enabled the use of supercritical fluids. Simultaneously, a deeper understanding of supercritical fluid behavior and its impact on separations led to optimal operating conditions for SFC. Today, SFC is a robust technique applied in everything from pharmaceutical analysis to food and beverage testing.

SFC is a powerful technique for separating and identifying various components within a compound. It leverages the unique properties of supercritical fluids, most commonly supercritical carbon dioxide, under high pressure to perform efficient and rapid separations of analytes with varying characteristics. Unlike traditional liquid or gas chromatography techniques, SFC is a hybrid of the two, providing a unique blend of efficiency and precision.

Fundamentally, SFC functions similarly to other chromatography techniques. A mixture to be separated is injected into a flow of supercritical fluid, also known as the mobile phase. This fluid is passed through a stationary phase, commonly a column containing silica gel, such as Teledyne LABS' RediSep columns.

The individual components of the mixture partition differently between the mobile and stationary phases due to their unique chemical properties. Those with higher affinity for the supercritical fluid move at a faster rate, while those favoring the stationary phase lag behind. As a result, the components are separated based on their individual partitioning behaviors.

The key to SFC's success lies in its unique mobile phase – the supercritical fluid. With a density similar to liquids but viscosity and diffusivity akin to gasses, supercritical fluids offer greatly enhanced diffusing power. These properties make SFC excellent for performing faster, cleaner, and more precise separations in complex mixtures.

The three states of matter are gas, liquid and solid. In the supercritical fluid region, matter under the influence of certain temperature and pressure levels becomes supercritical, where a difference between the gaseous and liquid states can no longer be observed.

In SFC, the mobile phase commonly used is supercritical carbon dioxide. Carbon dioxide is normally a gas (people and animals exhale it) and when it is under a certain pressure and cold enough, it forms dry ice. When the temperature and pressure reach a certain highpoint, the CO2 becomes supercritical.

Supercritical carbon dioxide is used in chromatography because it yields quick results and offers environmental advantages. It is stable, relatively inexpensive, non-flammable, non-toxic, and easy to remove from the sample. You can learn more about supercritical carbon dioxide here.

Because many compounds cannot be separated using supercritical CO2 alone, it usually is used in combination with another solvent, such as methanol, ethanol, and others.

  1. The mixture to be separated is introduced into the flow of supercritical fluid (the mobile phase).
  2. The mobile phase, bearing the sample, is passed over the stationary phase -- typically silica gel.
  3. The constituents of the mixture partition differently between the mobile and stationary phases, primarily governed by their individual physical and chemical properties.
  4. Analytes with higher affinity for the mobile phase transport faster, while those favoring the stationary phase move slower. As a result, they separate based on their partition coefficients.

SFC offers several advantages over traditional chromatography techniques. It provides high-precision separations in shorter time frames, making it highly efficient. It can accommodate a wide range of analytes due to the unique properties of supercritical fluids. The use of CO2, the most common supercritical fluid, offers environmental benefits due to its non-toxic nature and easy disposal.

However, not all substances are suited for SFC. Highly polar substances may not be efficiently separated with common supercritical fluids. Also, the set-up and maintenance of SFC systems can be comparatively complex due to the need for high-pressure equipment and careful temperature control. 

Despite these limitations, continuous advancements in technology and a better understanding of supercritical fluids are expanding the horizons for SFC applications. It is emerging as a strong contender to conventional chromatography techniques, promising a future where rapid, precise, and environmentally friendly separations will be more common.​

SFC has a wide range of applications. Due to its unique features and efficiency, it has been widely adopted in pharmaceutical analysis, environmental science, and food and beverage analysis. Its ability to analyze a vast variety of compounds, from volatile to nonvolatile and polar to nonpolar substances, makes it an ideal chromatographic technique.
Supercritical Fluid Chromatography in pharmaceutical ana​​lysis

SFC plays a vital role in the field of pharmaceuticals. Given its precision and accuracy in identifying the composition and purity of substances, it is increasingly being employed in drug discovery and development.

  • Drug discovery: Due to its high efficiency and resolving power, SFC is used to separate and analyze complex mixtures during the drug discovery process.
  • Quality control: SFC aids in the quality control of pharmaceutical products by detecting impurities, degradants, and chiral purity, ensuring that only high-quality medicines reach consumers.
  • Lipophilicity determination: SFC effectively determines the lipophilicity of drug molecules, an important property influencing drug absorption and distribution in the human body.

Moreover, with the aid of supercritical fluid extraction, SFC is used for the extraction of pharmaceuticals from their natural sources, significantly speeding up the production process.

Applications of Supercritical Fluid Chromatography in environmental science

In environmental science, SFC aids in the detection and analysis of pollutants and contaminants. 

  • Pesticide analysis: Pesticide residues in food and the environment can be efficiently detected and quantified using SFC, ensuring environmental and human safety.
  • Hydrocarbon analysis: SFC can analyze complex mixtures of hydrocarbons in petroleum products and determine the presence of specific compounds.
  • Soil analysis: SFC plays a significant role in soil sampling, detecting pollutants like polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and organochlorine pesticides.

In terms of aiding environmental sustainability, supercritical carbon dioxide extraction, a method employed in SFC, is used for the efficient extraction of natural resources, reducing the environmental impact.

Supercritical Fluid Chromatography for food and beverage analysis

SFC has become a staple in food and beverage analysis due to its ability to determine the composition, purity, and quality of food constituents. 

  • Food additives: SFC helps in the analysis and quantification of food additives and preservatives to ensure their levels are within safe limits.
  • Flavor profiling: It is used to create a flavor profile for beverages and foods by accurately identifying and quantifying the individual flavor compounds.
  • Nutrient analysis: SFC aids in the detection and quantification of nutrients in food, allowing for accurate labeling and dietary planning.

Supercritical carbon dioxide is also used in the decaffeination of coffee and tea, and the extraction of hops for beer production, demonstrating SFC's crucial role in the food and beverage industry.

​Frequently Asked Question​​​​s

What are some recent advancements in Supercritical Fluid Chromatography​?

Advancements in SFC technology have significantly boosted SFC's effectiveness and potential, making it even more vital in chemical analysis..

  • The introduction of Ultra High Performance SFC (UHPSFC) has increased the speed and resolution of SFC, enhancing productivity and efficiency in separation science.
  • Flow Modifier application has progressed, enabling better control over mobile phase properties, improving selectivity and providing more reliable results.
  • The use of polar stationary phases, such as diol and amide, has extended the range of compounds that can be analyzed by SFC, broadening its use to more complex and diverse samples.
What are some potential areas of future research for Supercritical Fluid Chromatography?

Considering the widespread application of SFC, there are several potential areas for future research and innovation.

  • Hardware and Software: Development and refinement of hardware and software can enhance the robustness and user-friendliness of SFC methods.
  • Green Chemistry: Exploring more environmentally friendly supercritical fluids and developing greener extraction and separation methods could align SFC more closely with sustainable chemistry practices.
  • Biotechnology: Investigating the application of SFC in the biotech sector, particularly in protein and enzyme analysis, can further extend its use.
What are some advantages of Supercritical Fluid Chromatography over HPLC?

While the principles of SFC are much like those of high-performance liquid chromatography (HPLC), the supercritical fluid used as the mobile phase offers decreased viscosity, allowing SFC to be run at a higher flow rate than HPLC. Therefore, SFC is generally a three to four times faster process than HPLC. Other advantages of SFC over HPLC include its “green” features:

  • Greatly reduces solvent consumption (up to eight times less organic solvent used)
  • Less solvent waste
  • Up to seven times lower energy consumption for solvent removal
  • CO2-neutral: reuses CO2 captured from other processes or the atmosphere
  • Environmentally friendly alternative to hazardous organic solvents
  • CO2 is nontoxic and with appropriate co-solvents is safe to use with food and pharmaceutical products