Phytochemical Screening and Antioxidant Activity of Selected Estonian Galium Species.

The aim of the present study was to examine three different Galium species from the native population of Estonia, Galium verum, Galium aparine, and Galium mollugo, to characterise their non-volatile and volatile phytochemical composition and antioxidant activity. The main groups of bioactive compounds in the plants were quantified by colorimetric tests, showing high concentrations of polyphenols (up to 27.2 ± 1.5 mg GAE/g), flavonoids (up to 7.3 ± 0.5 mg QE/g) and iridoids (up to 40.8 ± 2.9 mg AE/g). The species were compared using HPLC-DAD-MS/MS, revealing some key differences in the phytochemical makeup of the extracts. The most abundant compound in the extracts of Galium verum blossoms and herb was found to be asperuloside, in Galium aparine herb, asperulosidic acid, and in Galium mollugo herb, chlorogenic acid. Additionally, the composition of volatile compounds was analysed by SPME-GC-MS. The degree of variability between the samples was high, but three volatiles, hexanal, anethole, and ß-caryophyllene, were quantified (≥1%) in all analysed samples. The antioxidative activity of all extracts was evaluated using the ORACFL method, demonstrating that the Galium species from Estonia all exhibit strong antioxidant capacity (up to 9.3 ± 1.2 mg TE/g). Out of the extracts studied, Galium verum blossoms contained the highest amounts of bioactives and had the strongest antioxidant capacity.

Preparation and characterization of lignin-derived carbon aerogels.

Lignin is considered a valuable renewable resource for building new chemicals and materials, particularly resins and polymers. The aromatic nature of lignin suggests a synthetic route for synthesizing organic aerogels (AGs) similar to the aqueous polycondensation of resorcinol with formaldehyde (FA). The structure and reactivity of lignin largely depend on the severity of the isolation method used, which challenges the development of new organic and carbon materials. Resorcinol aerogels are considered a source of porous carbon material, while lignin-based aerogels also possess great potential for the development of carbon materials, having a high carbon yield with a high specific surface area and microporosity. In the present study, the birch hydrolysis lignin and organosolv lignin extracted from pine were used to prepare AGs with formaldehyde, with the addition of 5-methylresorcinol in the range of 75%-25%, yielding monolithic mesoporous aerogels with a relatively high specific surface area of up to 343.4 m2/g. The obtained lignin-based AGs were further used as raw materials for the preparation of porous carbon aerogels (CAs) under well-controlled pyrolysis conditions with the morphology, especially porosity and the specific surface area, being dependent on the origin of lignin and its content in the starting material.

Characterization of Organosolv Lignins and Their Application in the Preparation of Aerogels.

The production of novel materials and value-added chemicals from lignin has received considerable attention in recent years. Due to its abundant occurrence in nature, there is a growing interest in utilizing lignin as a feedstock for functional materials production, for example aerogels. Much like in the synthesis of phenol-based resins, the vacant ortho positions of the aromatic rings in lignin can crosslink with formaldehyde and form polymeric gels. After drying the hydrogels with supercritical CO2, highly porous aerogels are obtained. Current study focuses on the preparation and thorough parametrization of organosolv lignins from different types of lignocellulosic biomass (aspen, pine, and barley straw) as well as their utilization for the preparation of lignin-5-methylresorcinol-formaldehyde aerogels. The thorough structural characterization of the obtained aerogels was carried out by gas adsorption, IR spectroscopy, and scanning electron microscopy. The obtained lignin-based monolithic mesoporous aerogels had specific surface areas and total pore volumes in the upward ranges of 450 m2/g and 1.4 cm3/g, respectively.

Carbon aerogel-based solid-phase microextraction coating for the analysis of organophosphorus pesticides.

The current study is focused on the in situ synthesis of a carbon aerogel (CA)-based solid-phase microextraction (SPME) fiber coating on stainless steel wire and evaluation of the suitability of CAs as SPME coating materials for the analysis of selected organophosphorus pesticides (OPPs) contained in environmental samples. A CA-based coating was obtained by pyrolyzing organic aerogels, which were prepared by the sol-gel polymerization of formaldehyde and 5-methylresorcinol, an oil shale processing by-product. The results demonstrated, for the first time, the in situ synthesis of a CA-based SPME fiber coating on stainless steel wire and its suitability for the extraction and preconcentration of six OPPs. Main parameters affecting the extraction efficiency were investigated and optimized. The direct immersion (DI)-SPME procedure combined with gas chromatography-mass spectrometry (GC-MS) for the simultaneous analysis of selected OPPs was successfully applied to the efficient and sensitive determination of analytes of interest in environmental matrices of honey and natural water samples. The developed CA-coated SPME fiber showed good linearity (R2 = 0.981-0.994), low detection limits (0.11-0.83 µg L-1) and satisfactory single fiber and fiber-to-fiber reproducibilities (8.8-12.3%, n = 5 and 11.4-17.2%, n = 3). The performance of the CA-coating was compared with that of commercially available SPME fiber coatings.

Evaluation of carbon aerogel-based solid-phase extraction sorbent for the analysis of sulfur mustard degradation products in environmental water samples.

In this study, SPE method using a carbon aerogel(CA)-based sorbent was developed and evaluated for the simultaneous extraction of sulfur mustard (HD) degradation products from environmental water samples. Applied CAs proved to be very promising materials for use as SPE sorbents, due to their high porosity, very low density and a large specific surface area. 10 degradation products of HD, both aliphatic and cyclic (thiodiglycol (TDG), TDG sulfoxide, TDG sulfone, 3,5-dithia-1,7-heptanediol, 3,6-dithia-1,8-octanediol, 1,4-thioxane, 1,3-dithiolane, 1,4-dithiane, 1,2,5-trithiepane, and 1,4,5-oxadithiepane) were extracted on a CA-based SPE cartridge. The concentrations of target analytes in the eluate were determined by HPLC-DAD and CE-DAD. Several parameters affecting the extraction efficiency, including the kind and volume of the eluting solvent, sample loading flow rate, volume and ionic strength as well as the reusability of the cartridge, were investigated and optimized to achieve the best performance for the analytes. A series of quantitative parameters such as linear range, coefficient of determination, LOD, LOQ and precision were examined under the optimized conditions. High sensitivity (LODs 0.17-0.50 µM) and high precision (intraday RSD = 2.0-7.7% and interday RSD = 2.7-9.9%) for all the analytes were achieved. The performance of the CA-based sorbent was compared with that of commonly used SPE sorbents. Applied for the analysis of spiked pore water samples collected from the Bornholm Basin, one of the largest chemical warfare dumping sites in the Baltic Sea, the proposed method allowed high SPE recoveries of all the analytes ranging from 83.5 to 99.7% to be obtained.

Development of a capillary electrophoresis method with direct UV detection for the analysis of thiodiglycol and its oxidation products.

A novel method based on CE with precolumn derivatization and direct UV detection for the determination of thiodiglycol (TDG), TDG sulfoxide, and TDG sulfone in water samples was developed. The lack of a UV chromophore of target analytes was overcome by derivatization with phthalic anhydride. The reactant concentrations, as well as the derivatization dependence on heating temperature and time, were carefully investigated. The baseline separation of three derivatives was achieved in less than 8 min by applying a simple BGE composed of a 30 mM borate buffer at pH 8.5. Several parameters affecting the separation efficiency (buffer pH and concentration, capillary temperature, and applied voltage) were evaluated. Calibration curves of all compounds showed good linear correlations (R(2) > 0.9994). The LODs of the TDG and its oxidation products were in the range of 98-154 ng/mL. The precision tests resulted in RSDs for migration times and peak areas of less than 1.2 and 3.6%, respectively. The developed method was successfully applied for the analysis of TDG and oxidation products in seawater, utilizing the carbon aerogel-based adsorbents for sample purification and concentration. Additionally, the method has the potential to be transformed into a portable CE format.