Jasco takes chromatography supercritical

By Dr Matt Wilkinson

- Last updated on GMT

Related tags Chromatography

A new range of preparative scale supercritical fluid chromatography
(SFC) and extraction (SFE) products promises cheaper and faster
separations and extractions.

The new system was unveiled at this year's Pittcon and gives researchers the ability to extend the range of separation methodologies available in one system by also accommodating high performance liquid chromatography (HPLC) - reducing space requirements as well as initial outlay costs.

By using either supercritical CO2; or water, SFC reduces the environmental impact of a laboratory by reducing solvent use and the amount of solvent sent for disposal.

The system can be coupled to a variety of detectors, with Jasco offering a combined UV and circular dichroism detector option that allows the detection and quantification of the purity of chiral compounds.

This is particularly useful for pharmaceutical applications where one chiral enantiomer will give the desired pharmacological activity and the other may cause severe side effects.

Pharmaceutical companies had traditionally been reluctant to adopt SFC despite advances in instrumentation from the likes of Thar Technologies, Novasep, Jasco and Mettler-Toledo, because HPLC is perceived as the more versatile tool.

However, with the ability to combine both techniques into one instrument, Rich Cowman, chromatography specialist at Jasco believes that the time is ripe for SFC to finally deliver on its promises.

"All the pharmaceutical companies are saying that they need to go to SFC systems to save time and money," said Cowman.

When CO2's temperature and pressure is raised above the thermodynamic critical point it becomes supercritical CO2 (sCO2).

In this state the molecules have the unique ability to diffuse through solids like a gas while dissolving materials like a liquid.

This fact has been exploited for extraction applications since the 1950s, however its use as a mobile phase for chromatography has been hampered because polar compounds are often not soluble in the apolar sCO2.

However, in 2005, researchers from Virginia Polytechnic Institute and State University showed that the addition of small amounts of polar solvents such as methanol or isopropanol enabled these compounds to be solubilised.

According to Cowman, the supercritical CO2 mobile phase is less viscous and therefore diffuses better through the column packing, leading to increased separation efficiency which can be between three and five times faster than a standard HPLC system.

Jasco uses the example of a separation of the four tocopherol isomers of vitamin E to show the time savings, where a standard HPLC separation took 14 minutes and the SFC separation took 8 minutes.

It also claims that the solvents used in the HPLC separation cost $0.20 compared to $0.08 for the SFC separation.

The supercritical mobile phase is less aggressive to the mobile phase which increases the life of the column.

The systems utilise standard silica or ethyl-pyridine columns as well as chiral columns which allow the separation of racemic mixtures of chiral compounds.

The solvating power of the sCO2 depends on the pressure and temperature of the system with increasing pressure leading to increased solubility.

When the fluid is depressurised at the end of a separation or extraction the solute is precipitated.

This again saves time as lengthy drying procedures are not needed to recover the products as manageable products - a problem often associated with liquid chromatography techniques.

Another advantage of using sCO2 as a solvent is that it can be safely used for separating products for the pharmaceutical and food industries where the toxicity of solvents, and their residues, may be a problem.

By using a back-pressure regulator, such as Jasco's BP-2081, the pressure of the sCO2 can be changed without changing the flow rate.

This is especially useful for changing the solubility of the system during the separation, much like a temperature gradient in gas chromatography.

The system also allows the self-cleaning of any substances that have precipitated in the system during a separation.

The technique also finds application in the extraction of natural products from plant samples where the sample itself can be regarded as the stationary phase, often allowing the desired compounds to be specifically extracted.

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