Victor Abrahamsson

Determination of carotenoids in microalgae using supercritical fluid extraction and chromatography.

A method was developed based on supercritical fluid chromatography for quantitative determination of carotenoids in extracts of Scenedesmus sp. By utilizing the low backpressure in supercritical fluid chromatography, a C18 column and a 2-ethyl pyridine column were coupled in series. It was concluded that even minor changes in temperature had a substantial effect on selectivity. A standard mixture of 8 carotenoids and microalgae extracts obtained through supercritical fluid extraction with and without 10% ethanol as a co-solvent were successfully separated. All of the carotenoids were separated within 10 min, while the total analysis time was 20 min. The method was validated and the carotenoids of microalgae extracts were quantified. Furthermore, the method should be seen as a more rapid and environmentally sustainable alternative to traditional high-performance liquid chromatography methods utilizing organic solvents.

Extraction and Neoformation of Antioxidant Compounds by Pressurized Hot Water Extraction from Apple Byproducts

There is a great interest in searching for new environmentally sustainable techniques to enhance the use of agricultural byproducts. In this work, a response surface methodology was used to study the influence of the two independent variables, temperature (25-200 °C) and extraction time (3-17 min), in the extraction of antioxidants by pressurized hot water extraction (PHWE) from industrial apple byproducts. The optimized extraction method for determination of flavonols was at 120 °C and 3 min, giving a predicted total yield of flavonols of 1.3 μmol/g dry apple byproduct. Results obtained suggest that new antioxidant compounds were formed at the higher extraction temperatures. A desirability function response surface, considering maximum antioxidant capacity and minimal formation of brown color, was calculated and gave an optimum of 125 °C and 3 min. This latter PHWE method correlates well with the obtained results for flavonols; thus, a desirability function is a simpler alternative method for finding optimal conditions.

Impact of injection solvents on supercritical fluid chromatography.

Even though there has been a rapid development in instrumentation and applications of supercritical fluid chromatography (SFC), relatively little is known about retention mechanisms compared to high-performance liquid chromatography (HPLC). Much effort has been made to characterize the influence of injection solvents on chromatographic efficiency in HPLC, however has been left rather uninvestigated in the domain of SFC. In this study properties of different injection solvents have been studied and correlated with properties of seven various analytes on three different columns, a C18, a 2-ethylpyridine and a bare-silica column. Aided by calculations of correlation coefficients and principal component analysis (PCA), the physical properties of injection solvents and the interactions between injection solvent, solute and stationary phase were investigated. The findings of this work shows that interactions capable of masking accessible silanol groups on a C18 column are of importance in order to maximize the plate number. While solvents with dipolar and hydrogen bond interaction properties are associated negatively with chromatographic efficiency using polar columns. Properties such as molar density, vapor pressure and boiling point were related to sharper peaks, mostly likely because of solubility issues of the injection solvent into the methanol-modified carbon dioxide. However, no additional solubility due to hydrogen interactions between the injection solvent and the carbon dioxide in SFC was observed. Surface tension and viscosity was not particularly associated with a decrease in plate numbers. By increasing the injection volume a stronger correlation between solubility related properties and plate numbers were obtained. Additional experiments showed that the resistance in solubility became an issue when performing partial-loop injection where additional washing solvent entered the system, thus providing broadened peaks.

Supercritical fluid extraction of lipids from linseed with on-line evaporative light scattering detection.

Supercritical fluid extraction (SFE) is a green alternative method of extraction for neutral lipids in seeds compared to conventional methods utilizing organic solvents. In this work, a novel method where SFE is hyphenated with an evaporative light scattering detector is presented. The method was subsequently applied to determine lipid content in crushed linseed. The new method enables rapid quantification of extracted lipids as well as be ability to continuously monitor the extraction rate in real-time, thus being able to determine the time point of completed extraction. Both the detector and the method was validated. The results show that any of several tested oils can be used to calibrate the detection method for the determination of lipids extraction from linseed. The overall method repeatability and intermediate precision was 2.6% relative standard deviations. The extracted amount was significantly less than that obtained using the standard method of Soxhlet with petroleum ether, 26.0±0.4% (95% CI, n=9) compared to 32.3±1.3% (95% CI, n=3) of extracted amounts. It was found that channeling effects were present, and by either performing sequential repeated extractions with decompression in-between or by using a relatively large vessel a more complete extraction could be obtained. Interestingly, a substantially higher extracted amount (approximately 50%) was obtained compared to both a single extraction by SFE and the Soxhlet method. Therefore, it is recommended that an additional extraction including a rapid decompression in-between should be included in the validation of a method using supercritical fluid extraction, in order to either rule out channeling effects or to acquire a full recovery.

Comprehensive two-dimensional gas chromatography in combination with pixel-based analysis for fouling tendency prediction

Fouling tendencies of a series of gas condensates were evaluated using comprehensive two-dimensional gas chromatography with flame ionization detection and sulfur chemiluminescence detection. A pixel-based approach was applied in order to identify parts of the chromatograms which were associated with the reactor coil fouling. Particular emphasis is given in this work to evaluate several feature selection methodologies along with various data preprocessing procedures. It was found that both aspects were crucial for studying the fouling tendencies and, as part of the subsequent partial least squares model development, predominantly the feature selection. Based on the flame ionization detector chromatograms and using the RReliefF algorithm for feature selection, a partial least squares regression model with one latent variable resulted in a root mean square error of the cross-validation of 0.65gdeposit/6h (17%). Based on the sulfur chemiluminescence detector chromatograms, the F-statistics feature selection generated a slightly better partial least squares regression model compared to using RReliefF, thus generating a model using one latent variable with a root mean square error of the cross-validation of 0.81gdeposit/6h (21%). Heavy aromatic compounds and heavy sulfur containing compounds were negatively associated with the fouling rate. Both were crucial in developing a partial least squares model with good prediction power, however, worked independently as predictors.