(496e) Novel Approach to Study the Supercritical Fluid Extraction Process Continuously Using Evaporative Light Scattering Detection

As a part of the recent trends within analytical chemistry, it’s not uncommon to mention the three R’s in this context, namely Replace, Reduce and Recycle [1]. That is also why the supercritical fluid extraction (SFE) in theory is the ideal extraction method due to the usage of CO₂ instead of organic solvents. Even though its established use, much work remains in characterizing the fundamentals of the extraction process. The fundamental knowledge gained studying analytical scaled systems can subsequently be used in for example modelling of larger systems.

Modelling in general requires experimental data for calibration which is not easily obtained with good accuracy in large quantities. A popular approach is to sample fractions during the extraction process or terminating the extraction at various time points. Both approaches are time consuming and may cause an inflation of the experimental error. On-line detection for continuously monitoring the process enables the acquisition of accurate data in large quantities with reasonable effort. Previous examples exist using for example UV-Vis and FTIR detectors [2]. These may however limit operating boundaries of the SFE system with regards to pressure due to the flow cell of the detectors. Also the use of UV-Vis detectors requires that the compounds of interest have a chromophore in order to be efficiently detected.

A novel approach has been developed to study the extraction in real-time by coupling an evaporative light scattering detector (ELSD) to a continuous SFE system. The ELSD offers universal detection thus not requiring that compounds of interest readily absorb light in the UV-Vis part of the spectrum. The fact that it is coupled after the depressurization means that it does not limit the maximum pressure of the system.

The SFE-ELSD system was validated by applying it to crushed linseeds with the purpose of quantifying the total amount of oil. A full validation was performed in order to ensure good quality of the measurements. The precision was considered good with a repeatability and reproducibility of 2.6% and the accuracy of the ELSD was in well agreement with a gravimetric determination subsequent the extraction.

The newly developed system was subsequently used to study the extraction process of lipids from crushed linseeds at various extraction conditions. It was also noted that by performing repeated extractions using an analytical scale extraction vessel the yield increased immensely. The accumulated yield was approximately doubled compared to the first single extraction, and the yield was far greater than that of the commonly used reference method using Soxhlet with petroleum ether. Some claims have been made that compression and decompression can rupture the matrix and thus increasing total available content [3]. However by utilizing the proposed SFE-ELSD system we believe that these findings are rather related to channeling effects than rupturing of the sample matrix.

In addition some preliminary evaluation of models using the data acquired from the SFE-ELSD system will be presented.

1.         Welch, C.J., et al., Greening analytical chromatography. TrAC - Trends in Analytical Chemistry, 2010. 29(7): p. 667-680.

2.         Amador-Hernández, J. and M.D. Luque De Castro, On-line detection for supercritical-fluid extraction. Journal of Biochemical and Biophysical Methods, 2000. 43(1-3): p. 329-343.

3.         Barthet, V.J. and J.K. Daun, An evaluation of supercritical fluid extraction as an analytical tool to determine fat in canola, flax, solin, and mustard. JAOCS, Journal of the American Oil Chemists' Society, 2002. 79(3): p. 245-251.