Background and aims Only the carbon (C) isotope pulse labeling approach can provide time-resolved data concerning the input and turnover of plant-derived C in the soil, which are urgently needed to ...improve the performance of terrestrial C cycle models. However, there is currently very limited information about the point in time after pulse labeling at which the distribution of tracer C accurately represents the usage of photosynthates in different components of the plant-soil system. This should be the case as soon as the tracer has disappeared from the mobile C pool due to respiration, incorporation into the structural C pool of shoot and root tissue and exudation into the soil (rhizodeposition). Methods Following pulse labeling in laboratory and outdoor experiments with spring rye, the .sup.14C dilution rates of soluble fractions and different substances from the structural C pool of the shoot (molecular level), the release of labeled CO.sub.2 by belowground respiration (component level), and the .sup.14C kinetics of shoot respiration and .sup.14C remaining in the plant-soil-soil gas continuum (system level) were analyzed during different stages of plant development. Results At all three levels investigated, .sup.14C kinetics indicated that the C tracer levels changed very little between 15 and 21 days after labeling. Results also showed increasing tracer depletion in the mobile C pool. Consequently, only 0.42 % and 0.06 % of all .sup.14C was still available for shoot respiration 15 and 21 days after labeling, respectively. Conclusions The similarities between .sup.14C tracer kinetics at the three investigated levels indicate that tracer disappearance from the mobile pool and distribution throughout the plant-soil system was nearly complete between 15 and 21 days after labeling. Therefore, this appears to be the point at which the pulse labeling approach provides sufficiently precise data concerning the use of C (assimilated during labeling) for root growth, rhizodeposition, root respiration and the microbial turnover of rhizodeposits.
Solid Phase Microextraction (SPME) has been introduced as a modern alternative to current sample preparation technology, and has a wide range of applications. Focusing on quantitative aspects of ...analysis, Applications of Solid Phase Microextraction aims to describe these applications. In industry, practical uses of SPME can be found in environmental, food, pharmaceutical, clinical and forensic applications, all of which are described in this book. Important scientific applications such as reaction monitoring, characterization of coatings and distributions of analytes in natural multiphase systems are also discussed. Throughout there are descriptions of new technologies, including new coatings and interfaces for analytical instrumentation (SPME/LC and SPME/CE), automation and calibration processes. Written by internationally recognised experts, edited by the scientist involved in the research since its infancy, and encompassing a wide range of applications, this book will be ideal for anyone wishing to explore the feasibility of using SPME technology.
Solid-phase microextraction (SPME) in both conventional and headspace mode was used for determining the freely available and reversibly bound fraction of phenols and polycyclic aromatic hydrocarbons ...in contaminated water rich in dissolved polymeric organic matter (DOM). The SPME results obtained by using internal calibration with deuterated surrogates gave the total analyte concentration based on the identical partitioning behaviour of both, native pollutants and deuterated spikes, and agreed well with data from exhaustive LLE. Data obtained with direct and headspace SPME are very similar. Investigated matrices include both contaminated water and artificial DOM solutions. The DOM compounds were isolated from different aquatic and terrestrial sources and cover a wide range of hydrophobicity. A new approach based on progressive dilution of samples rich in DOM was developed for determining both the freely-dissolved fraction of an unknown analyte and its partition coefficients. Theoretical considerations provide strong evidence that the commonly used term `concentration' in SPME analysis should be replaced by the more appropriate term `activity' of the solute.
Pressurized liquid extraction was combined with in-situ derivatisation to extract polar analytes such as phenols (including chlorophenols) sterols and carboxylic acids from environmental and ...microbial samples. This one-step protocol uses acetic anhydride as an acetylation agent, N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) as an silylation agent, and boron trifluoride–methanol, phenyltrimethyl ammoniumhydroxide and trimethyl sulfoniumhydroxide as methylation agents. It results in faster extraction rates and better or comparable extraction efficiencies when compared to classical approaches. The addition of a silylation agent also facilitates the extraction kinetics of analytes not accessible to silylation (e.g. polycyclic aromatic hydrocarbons or alkylbenzenes). This may be attributed to a dissociative action of the agent to weaken analyte–matrix interactions.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Background and aims Only the carbon (C) isotope pulse labeling approach can provide time-resolved data concerning the input ...and turnover of plant-derived C in the soil, which are urgently needed to improve the performance of terrestrial C cycle models. However, there is currently very limited information about the point in time after pulse labeling at which the distribution of tracer C accurately represents the usage of photosynthates in different components of the plant-soil system. This should be the case as soon as the tracer has disappeared from the mobile C pool due to respiration, incorporation into the structural C pool of shoot and root tissue and exudation into the soil (rhizodeposition). Methods Following ... pulse labeling in laboratory and outdoor experiments with spring rye, the 14C dilution rates of soluble fractions and different substances from the structural C pool of the shoot (molecular level), the release of labeled CO2 by belowground respiration (component level), and the 14C kinetics of shoot respiration and 14C remaining in the plant-soil-soil gas continuum (system level) were analyzed during different stages of plant development. Results At all three levels investigated, 14C kinetics indicated that the C tracer levels changed very little between 15 and 21 days after labeling. Results also showed increasing tracer depletion in the mobile C pool. Consequently, only 0.42 % and 0.06 % of all 14C was still available for shoot respiration 15 and 21 days after labeling, respectively. Conclusions The similarities between 14C tracer kinetics at the three investigated levels indicate that tracer disappearance from the mobile pool and distribution throughout the plant-soil system was nearly complete between 15 and 21 days after labeling. Therefore, this appears to be the point at which the pulse labeling approach provides sufficiently precise data concerning the use of C (assimilated during labeling) for root growth, rhizodeposition, root respiration and the microbial turnover of rhizodeposits.
Background and aims Only the carbon (C) isotope pulse labeling approach can provide time-resolved data concerning the input and turnover of plant-derived C in the soil, which are urgently needed to ...improve the performance of terrestrial C cycle models. However, there is currently very limited information about the point in time after pulse labeling at which the distribution of tracer C accurately represents the usage of photosynthates in different components of the plant-soil system. This should be the case as soon as the tracer has disappeared from the mobile C pool due to respiration, incorporation into the structural C soil (rhizodeposition). Methods Following ¹⁴CO₂ pulse labeling in laboratory and outdoor experiments with spring rye, the ¹⁴C dilution rates of soluble fractions and different substances from the structural C pool of the shoot (molecular level), the release of labeled CO₂ by belowground respiration (component level), and the ¹⁴C kinetics of shoot respiration and ¹⁴C remaining in the plant-soil-soil gas continuum (system level) were analyzed during different stages of plant development. Results At all three levels investigated, ¹⁴C kinetics indicated that the C tracer levels changed very little between 15 and 21 days after labeling. Results also showed increasing tracer depletion in the mobile C pool. Consequently, only 0.42% and 0.06% of all ¹⁴C was still available for shoot respiration 15 and 21 days after labeling, respectively. Conclusions The similarities between ¹⁴C tracer kinetics at the three investigated levels indicate that tracer disappearance from the mobile pool and distribution throughout the plant-soil system was nearly complete between 15 and 21 days after labeling. Therefore, this appears to be the point at which the pulse labeling approach provides sufficiently precise data concerning the use of C (assimilated during labeling) for root growth, rhizodeposition, root respiration and the microbial turnover of rhizodeposits.
Identification of bovine and ovine tissue from the central nervous system (CNS: brain and spinal cord) in meat products is possible by using certain CNS fatty acids as biomarkers in GC-MS analysis. ...Furthermore, the relationship between the isomers of the tetracosenic acid (C24:1) is important for differentiation of the species and age of the CNS in view of the legal definition of specified risk material (SRM). This has so far been referred to as the "cis/trans ratio of the isomers of nervonic acid"; however, structural analysis was not performed. Here we present results from GC-MS structural analysis by retention time and DMDS adduct profiling of the even numbered monoenoic fatty acids from C18:1 to C26:1. Retention times and mass spectra of the FAME standards indicated that the so far designated trans-nervonic acid has a different isomeric structure in the tetracosenic acid from brain-sample extracts. By performing GC-MS analysis of DMDS adducts we have shown that this isomer was actually cis-17-tetracosenic acid in all species so far tested, not trans-15-tetracosenic acid ( trans-nervonic acid). The tetracosenic acid isomer ratio proved to be species-specific in accordance with previous results. Thus, instead of the ratio of cis/trans isomers of nervonic acid, the ratio of omega 9/omega 7-tetracosenic acid (15c-C24:1/17c-C24:1) will have to be used as a correct reference in future publications. Although trans isomers were not detectable in sheep and cattle brain, porcine brain contained, in addition to cis-17-tetracosenic acid, small amounts of the trans isomers of the C18:1, C20:1, C24:1, and C26:1 fatty acids, in decreasing quantities. In future, this might be useful as another means of differentiation between porcine CNS (non-SRM) and ovine or bovine CNS (SRM). Extensive follow-up studies must be performed to elucidate the extent to which this GC-MS approach will facilitate the detection of CNS according to the legal SRM definition.
Supercritical fluid extraction using supercritical carbon dioxide was applied to extract nitroaromatic compounds covering a wide range of polarity from soils having high humic organic matter content. ...Commercially available non-ionic, anionic and cationic surfactants were utilised as modifiers to enhance analyte solubility in the fluid.
The applied surfactants turned out to have no significant beneficial impact on target analyte recoveries. On the contrary, surfactants exercise a detrimental effect on recovery by the formation of a “layer” on the soil or by “plugging” micropores, thus hampering analyte desorption. The surfactant deposition onto the soil under supercritical conditions was traced using electrospray ionisation mass spectrometry. The surfactant can be fully solubilised by adding polar methanol modifier to the fluid, but there was no synergetic effect between surfactant and modifier.