The bark of trees contains an interesting mixture of bioactive compounds, or so-called extractives. The use of supercritical carbon dioxide (sc-CO2) eliminates both the need for organic solvents as extractants and the danger that solvent traces might compromise the purity of the extracts. Unfortunately, the complexity and natural variability of extracts’ composition render any utilization attempts rather challenging. Thus, in order to implement exploitation concepts in a meaningful way, appropriate analytical techniques for characterizing extracts must be available beforehand. In our work, we explored gas chromatography coupled to both mass spectrometry and a flame ionization detector (GC-MS/FID), in combination with ultraperformance convergence chromatography and quadrupole time-of-flight mass spectrometry (UPC2-QTof-MS), for the characterization of bark extracts from pine (Pinus sylvestris L.) in both qualitative and quantitative terms. Although the conventional GC-MS/FID approach is a robust method for overall quantification of extractives, it fails to provide ample information about native sterol esters and triglycerides. These data are provided by a new, complementary analytical technique based on supercritical carbon dioxide, as the chromatographic eluant, coupled to a high-resolution mass spectrometer. The combination of both techniques and the use of sc-CO2 as both an extraction solvent and eluant made this combined tool especially powerful. The most prominent triglycerides in the extract were identified qualitatively and quantitatively, and the dominating sterol esters were identified qualitatively, by UPC2-QTof-MS.
The impact of totally chlorine-free (TCF) bleaching chemicals on the composition and behavior of detrimental lipophilic wood extractives in a mixed hardwood sulfite pulp was studied to determine their potential for pitch control without the need for additional reagents. Toward this end, the acetone extracts of pulp were analyzed with commonly used gas chromatography (GC) and more sophisticated ultraperformance convergence chromatography (UPC2). During EO(P)–Z–P bleaching, the highest decrease in the lipophilic extractive content was achieved after ozone bleaching (Z), with a 38% reduction of GC-FID/MS-detectable resins. Oxygen-reinforced alkaline extraction EO(P) and peroxide bleaching (P) were less effective in terms of resin quality and quantity (−30 and −27%, respectively). Analyzing the acetone extracts after alkaline hydrolysis revealed a different pattern: EO(P) with −44%, P with −20%, and Z with only −8% less lipophilic extractives. A series of oxidized compounds, such as acyl chain-oxidized sterol esters and acylglycerols, and acidic secosterol analogues, were detected for the first time with UPC2-ESI-QToF-MS after ozone bleaching. These compounds lead to an underestimation of the GC-detectable resin content and may be involved in the formation of deposits during lignocellulosic processing. Reaction pathways for lipophilic extractives during ozone bleaching were established.
The extraction of lipophilic wood extractives from pulp and paper process waters proves to be a challenging task, due to harsh and alternating process and sample conditions. This study has determined the potential use of polymeric sorbents for solid-phase extraction (SPE) and compared to classical silica-based reversed-phase packed columns, with polymeric hydrophilic-lipophilic balanced (HLB) cartridges being the sorbent with the most potential. Recovery functions were obtained with an internal standard mixture representative for the main lipophilic wood extractive groups, which are fatty acids and alcohols, sterols, sterol esters and triglycerides. The impact of pH, sample volume and sample matrix, expressed as TOC and cations, on the retention behavior of lipophilic extractives during SPE of industrial samples were determined with polymeric HLB sorbent. High variations in the composition of pulp mill matrices led to different optimal extraction conditions. Thus, a new SPE protocol was developed, which bypasses matrix interferences and omits the loss of analytes due to sample preparation. The method is applicable to different pulp mill effluents with large discrepancies in pH and sample matrices, resulting in recoveries >90 % with RSD <5 % for all lipophilic wood extractives.
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