Separation Science

Quantification of Compounds in the E7 Liquid Crystal Mixture by Supercritical Fluid Chromatography with UV Detection

Agilent Technologies has produced an application note demonstrating the capability of the Agilent 1260 Infinity Analytical SFC system to perform quantitative analysis of liquid crystal compounds. It demonstrates that fast separation of commercial liquid crystal mixtures is possible within a few minutes. Detection was done by UV, and a relative quantification of the composition of the E7 mixture is described. The results are supported by a statistical evaluation.

Agilent_compounds_E7_liquid_crystal_mixture.pngIntroduction
Liquid crystal is a type of matter that has physical properties between the solid state and the liquid state. Liquid crystals can be obtained in thermotropic, lyotropic, and metallotripic phases. The thermotropic liquid crystals are, for example, rod-shaped organic molecules. They exhibit a phase transition to the liquid crystal phase with change of temperature. Typically, below a certain temperature range, thermotropic liquid crystals behave like a solid, and above like a liquid. Within the range of liquid crystallinity, they may show some nematic and smectic phases. In the nematic phases, rod-shaped molecules typically order along their axis and align to magnetic and electric fields. In smectic phases, the molecules are ordered in layers.

In this application, the quantification of all compounds is demonstrated by creation of the respective calibration curves after UV detection. The relative quantifcation of the content of a commercially available liquid crystal mixture is shown.

Results and Discussion
From the individual stock solutions of the liquid crystal compounds 5CB, 7CB, 8OCB, and 5CT, a mixed stock solution was generated. This solution was used for the development of the SFC separation method. The single wavelength at 280 nm for the detection of all compounds was determined from individual spectra, where the response of all compounds was sufficient. The developed method separated the four similar compounds between 1.38 minutes and 1.73 minutes.

Conclusion
The baseline separation of a mixture of four liquid crystal compounds of technical importance is demonstrated in a fast, 2.25-minute run time. This fast run time is about a factor of 20-times faster than the typically used conventional RP-HPLC separations. The retention time RSDs are below 0.25 %, and the calibration curve linearity is better than 0.99990. The quantitative determination of the
composition of a commercial E7 liquid crystal mixture is demonstrated.

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