Supercritical Fluid Chromatography - Fourier Transform Infrared Spectroscopy (SFC-FTIR)

Supercritical Fluid Chromatography - Fourier Transform Infrared Spectroscopy (SFC-FTIR)

At present, the hyphenated technology in the field of modern analytical chemistry technology is developing rapidly and has occupied an important position, and its application is very extensive. Supercritical fluid chromatography-Fourier infrared spectroscopy (SFC-FTIR) technology is a promising hyphenated technology that is newly developed.

Supercritical Fluid Chromatography

Supercritical fluid chromatography (SFC) is a chromatographic method that uses supercritical fluid as the mobile phase. It is a chromatographic branch that has developed rapidly since the 1980s. The so-called supercritical fluid refers to a state of matter above the critical pressure and critical temperature. It is neither a gas nor a liquid, but it has the characteristics of low viscosity of gas, high density of liquid, and higher diffusion coefficient between liquid and gas. SFC can analyze thermally unstable, higher boiling point, and larger molecular weight substances that are difficult to handle by GC at a lower temperature. It also has higher column efficiency and faster separation speed than HPLC. Generally, SFC uses detectors commonly used in GC or HPLC, such as UV detectors. As more and more attention is paid to structural information detectors, SFC can also be used online with mass spectrometry (MS) and Fourier infrared spectroscopy (FTIR). Therefore, SFC can facilitate the qualitative and quantitative analysis of substances. Although SFC can make up for some of the shortcomings of GC and LC, it cannot completely replace GC and LC. Therefore, SFC is a complementary method in chromatographic analysis.

Fourier Transform Infrared Spectroscopy (FTIR)

The Fourier transform infrared spectrometer is different from the principle of dispersive infrared spectroscopy. It is an infrared spectrometer developed based on the principle of Fourier transform of infrared light after interference. Fourier transform infrared spectrometer is mainly composed of infrared light source, interferometer, sample chamber, detector, computer data processing system and power supply. Fourier transform infrared spectrometer has the advantages of high signal-to-noise ratio, good reproducibility, and fast scanning speed. It can perform qualitative and quantitative analysis of samples and is widely used in medicine, chemical industry, petroleum, coal, environmental protection and other fields.

Supercritical Fluid Chromatography - Fourier Transform Infrared Spectroscopy (SFC-FTIR)

FTIR has a strong resolving power, which can completely identify the overall structure information of the tested substance. But the separation ability of FTIR is much weaker than that of SFC. Most SFCs use carbon dioxide as the mobile phase, which has advantages such as good solubility. Supercritical carbon dioxide only exhibits strong infrared absorption at 3800~3500 cm-1 and 2500~2200 cm-1. Therefore, supercritical carbon dioxide is also a good solvent for infrared spectroscopy. The combination of SFC-FTIR technology effectively combines the characteristics of the two analysis methods and exerts a greater advantage. SFC-FTIR can be used as an effective means to analyze and identify complex organic mixtures, giving the functional group information of the entire analyte molecule. SFC-FTIR, GC-FTIR and HPLC-FTIR are complementary analytical methods.

The interface method of SFC-FTIR is similar to that of liquid chromatography, which is divided into flow cell method and mobile phase removal method.

  • Flow cell method
  • The flow cell is the most important part of SFC-FTIR. The flow cell method uses a subtraction method to deduct the interference of the mobile phase spectrum, and has the advantages of simple equipment and convenient operation. But the flow cell method also has shortcomings. When the pressure rises, the absorption of carbon dioxide will increase and cause the baseline of the spectrum to rise, which will interfere with the chromatographic peaks. In addition, due to the existence of the strong infrared absorption peak of carbon dioxide, alcohol, nitrile and alkyne compounds cannot be detected. The flow cell method also restricts the use of polar modifiers.

  • Mobile phase removal method
  • The mobile phase removal method is a method of collecting SFC fractions and then performing spectral measurement. The advantages of the mobile phase removal method are high sensitivity, easy spectral analysis and retrieval, and various mobile phases can be selected according to chromatographic requirements. However, the mobile phase removal method has disadvantages such as complicated equipment and complicated operation, which is not conducive to the detection of low boiling point compounds.

As a new type of analysis technology, SFC-FTIR needs to be continuously updated and improved in many places. With the continuous updating of technology, SFC-FTIR is bound to have more rapid development.

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