A home-made silica-based silver ion solid-phase extraction (Ag + -SPE) system for the fractionation and subsequent gas chromatographic analysis of trans fatty acids in human adipose tissue is developed and examined. Analytical characteristics of the home-made Ag + -SPE column were compared with those of the commercial Discovery Ag-Ion SPE column and it was demonstrated that the both columns can be applied for the fractionation of fatty acid methyl esters.
A monolithic silica sorbent has been successfully synthesized and modified with aminopropyl groups. The modification was achieved by the reaction of (3‐aminopropyl)triethoxysilane and silanol groups on the sorbent surface. For the formation of silver nanoparticles on the aminopropyl groups modified monolithic sorbent, silver nitrate was used as a precursor and formaldehyde as a reducing reagent. Prepared sorbent was tested for pre‐separation of trans fatty acids methyl esters followed by gas chromatography analysis. Due to the interaction between the silver nanoparticles on sorbent surface and double bounds of fatty acids methyl esters, fractionation based on a number of double bounds and on the configuration was achieved.
Static headspace gas chromatographic method for determination of hexanal as a marker of lipid oxidation was developed. Tetradecane was suggested as a matrix for hexanal release from the sample. Sample equilibration temperature and time, tetradecane volume, injection time were optimized. Benzaldehyde was selected as an internal standard. Under the optimized conditions quality parameters were determined. The calibration curve was linear in the concentration range from 25 µg l -1 to 2 g l -1 , the detection limit was 15 µg l -1 , RSD was determined by five replication analysis with hexanal concentration 0.1 g l -1 and was 1.2%. The technique was applied for hexanal determination in potato chips and fried potatoes.
Direct and headspace gas chromatographic analysis is compared for the determination of lactic, oxalic, succinic, malic and citric acids. For better chromatographic behaviour, prior to GC analysis carboxylic acids were derivatized using BSTFA as a silylation reagent. Three solvents – acetone, diethyl ether and dimethylformamide – were tested as a derivatization medium and DMF was considered as the best. Derivatization conditions were optimized and analytical characteristics of the direct gas chromatographic determination of analytes in solutions were determined. The method was applied for the determination of citric acid in food. For the analytes dissolved in DMF, the headspace gas chromatographic determination was not sensitive enough. Concentrations of the derivates in the headspace were very low, thus the limits of detection were high and the method was not of practical use. On the other hand, headspace gas chromatography can be applied for identifying of carboxylic acids in solid samples.
Oxidation of unsaturated fatty acids of edible oils results in off-flavours, in a decrease in the nutritional properties and in the formation of toxic compounds. Hexanal is a suitable marker of the oxidation process. A new solvent, coconut oil, was suggested for hexanal quantification by static headspace extraction-gas chromatography. Sample equilibration temperature, time, weight and injection time were determined to provide the highest extraction to the headspace efficiency. At the optimized extraction conditions, the hexanal detection limit was 30 µg kg–1, linearity was 0.9977 for a concentration range of 50 µg kg–1 – 2 g kg–1 and repeatability of the results was 1.1%. The effect of heating on hexanal formation in four edible oils (olive oil, sunflower oil, rapeseed oil and linseed oil) was investigated. The biggest quantity of hexanal was observed in sunflower oil and it significantly increased after heating. Rapeseed oil was the most resistant to the oxidation at elevated temperatures. For linseed oil hexanal is not the most relevant oxidation marker as hexanal is not the main volatile oxidation product.
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