Marker compounds, distributions

Nonetheless the approach can provide - both routinely and rapidly - large amounts of pharmacokinetic or other distribution information on several compounds without significantly increasing the burden on the animals, whilst also minimizing the number of animals used. It is common to include a compound of known pharmacokinetics that acts as a control in each of these studies. This can help in identifying when the co-administered compounds have changed the kinetics. However, such marker compounds will not necessarily highlight problems with compounds that are subject to different clearance mechanisms [35],... 

Other Experimental Methods. It is probably suitable to discuss here column porous structure. Porous space of a conventional packed column consists of the interparticle volume (Vip—space around particles of packing) and pore volume (Vp— space inside porous particles). The sum of those two constitutes the column void volume. The void volume marker ( unretained ) should be able to evenly distribute itself in these volumes while moving through the column. Only in this case the statistical center mass of its peak will represent the true volume of the Uquid phase in the column. In other words, its chromatographic behavior should be similar to that of the eluent molecules in a monocomponent eluent. If a chosen void volume marker compound has some preferential interaction with the stationary phase compared to that of the eluent molecules, it will show positive retention and could not be used as void marker. If on the other hand it has weaker interaction, it will be excluded from the adsorbent surface and will elute faster than the real void time, meaning that it also could not be used. For any analytical applications (when no thermodynamic dependences are not extracted from experimental data), 10% or 15% error in the determination of the void volume are acceptable. It is generally recommended to avoid elution of the component of interest with a retention factor lower than 1.5. Accurate methods for the determination of the column void volume are discussed in Chapter 2. 

Sagebiel, J.C., Seiber, J.N. (1993) Studies on the occurrence and distribution of wood smoke marker compounds in foggy atmospheres. Environ. Toxicol. Chem. 12, 813-822. 

By virtue of where, when, and how the various organic matter inputs were formed and transported to the underlying sediments, it is possible to exploit specific chemical and isotopic characteristics to make inferences about the sources and composition of sedimentary organic matter. Much of this information is inaccessible at the bulk level. For example, bulk elemental compositions and stable carbon isotopic compositions are often insufficiently unique to distinguish and quantify sedimentary inputs. Abundances and distributions of source-specific organic compounds ( biomarkers ) can help to identify specific inputs. However, this molecular marker approach suffers from the fact that the source diagnostic marker compounds are... 

Distributions of carotenoids can be characteristic for various groups of photosynthetic organisms. Fucoxan-thin is characteristic of diatoms (BaciUariophyceae) and peridinin is found in many dinoflagellates (Dinophyceae Fig. 2.23). In contrast, diatoxanthin and diadinoxanthin occur in many phytoplanktonic classes due to their xanthophyll cycle role (Fig. 2.25).Although it is a less specific marker compound, (3-carotene is abundant in cyanobacteria. Photosynthetic bacteria produce acyclic and aromatic carotenoids (e.g. lycopene and okenone, respectively Fig. 2.23). Astaxanthin and its esters are major constituents of marine zooplankton (Fig. 2.23). 

Chapter 2 contains two studies related to groundwater contamination as a result of two different anthropogenic activities. The first study (chapter 2.1) focuses on emissions derived from a leaking waste deposit landfill. The chemical characterisation as well as the identification of specific contaminants are main objectives. Further on, using a set of specific waste deposit derived marker compounds the spatial distribution as well as a time trend was characterised in order to assess the risk of the waste deposit derived effluents. 

For monitoring the spatial distribution of the landfill derived contamination the selected marker compounds were quantified in 5 groundwater wells at two different levels as indicated in Fig. 2. Selected quantitative data are also presented in Fig. 2. NBBS was excluded in this marker analyses due to an artificial contamination of the water samples during the pumping operation by plasticizers released by plastic fittings. 

The GC/MS non-target screening analyses revealed numerous compounds of which selected ones are subsequently presented and discussed in the following mainly with respect to their source specifity and their spatial distribution within the riverine system. Concentrations of anthropogenic marker compounds as well as of still unnoticed contaminants will effectively characterize anthropogenic emissions and provide a more detailed view on the pollution of the Lippe river. All quantitative data are shown in Tab. 2 a-d. 

Fig. 4 Distribution patterns of the three gathered industrial marker compound in samples from the campaign of August 1999...

Considering the spatial distribution of the chlorinated marker compounds (bischloropropylethers, chlorinated butadienes and OCS) a significant contribution of effluents from chlorochemical industry has to be stated for samples from locations 1 and 2. In fact there is a settlement of several chemical plants nearby sampling location 2. Hence, it is obvious... 

Hence, for the evaluation of the proposed Elbe marker compounds the quantitative and spatial distribution as illustrated for selected substances in Fig. 1 and 2 are the most important criteria. The quantitative evaluation of the molecular markers has to consider the accumulation rates of organic matter at the different sampling sites. Thus, in order to avoid misinterpretation all quantitative data presented in Fig.l and 2 are normalized to TOC content (given in pg/kg TOC). 

Di- and trichlorinated benzenes were detected not only at sample sites mainly influenced by the Elbe river but also at sampling sites G and D, which are mainly influenced by input of the Ems river, with similar concentrations as in samples E and F (see Tab. 2). Hence these lower substituted compounds, which are used as synthetic raw material for many technical products such as antiseptic agents, solvents and additives (Biyant, 1993), are not appropriate marker compounds for tracing Elbe river derived contaminations. In contrast the tetra- to hexachlorinated benzenes, which have formerly been identified as contaminants in particulate matter of the Elbe river system (Schwarzbauer 1997, Schwarzbauer et al. 2001), appeared in the North Sea sediments only at sampling sites A,B,C,E and F (see Tab. 2). Fig. 1 illustrates the spatial distribution of hexachlorobenzene with concentrations between 2 and 50 pg/kg TOC in samples influenced by the Elbe river. 

Fig. 1 Concentration and spatial distribution of selected Elbe specific marker compounds in sediments of the German Bight (all data are given in pg/kg dry matter and normalized to TOC). All abbreviations of the substances are explained in Tab. 2. The dotted lines indicate the main flow circle of the water body according to Ducrotoy et al. (2000).

As illustrated in Fig. 1 for 2,2-bis(4-chlorophenyl)-l,l-dichloroethane (4,4 -DDD) higher concentrations (25 to 47 pg/kg TOC) were observed at sampling sites A, B and C, whereas the concentrations decreased at sites D, E and F (1, 7 and 5 pg/kg TOC, respectively). At sampling location G, which is not influenced by Elbe river derived sedimentary matter, the concentration of 4,4 -DDD fell below the LOQ. A similar distribution was observed for 2,2-bis(4-chlorophenyl)-l,l-dichloroethene (4,4 -DDE) (see Tab. 3). Low concentrations of DDT metabolites bis(4-chlorophenyl)acetonitrile (4,4 -DDCN) and 2,4 -DDD were detected only at sampling site B. The concentrations of DDD, DDE and DDCN analysed in the North Sea sediments reflect a significant proportion of Elbe derived DDT metabolites in sediments of the German Bight and confirm DDT related compounds as appropriate Elbe marker compounds. 

Selected contaminants were quantified in seven sediment samples of the German Bight. The compounds analysed include substances formerly proposed as Elbe specific marker compounds and contaminants reflecting a diffuse contribution to the pollution of North Sea sediments. For the evaluation of the proposed Elbe marker compounds the quantitative and spatial distribution was investigated and discussed as the most important criterion to define their source specifity. 

For the evaluation of these proposed Elbe marker compounds the quantitative and spatial distribution was investigated. These data provide an important criterion to define their source specifity. 

GC and GC-MS (see Chapter 2), are ideal for the separation and characterization of individual molecular species. Characterization generally relies on the principle of chemotaxonomy, where the presence of a specific compound or distribution of compounds in the ancient sample is matched with its presence in a contemporary authentic substance. The use of such 6molecular markers is not without its problems, since many compounds are widely distributed in a range of materials, and the composition of ancient samples may have been altered significantly during preparation, use and subsequent burial. Other spectroscopic techniques offer valuable complementary information. For example, infrared (IR) spectroscopy and 13C nuclear magnetic resonance (NMR) spectroscopy have also been applied. 

Such requirements are expected to assure that the dosage form is formulated and manufactured appropriately to ensure that the index or marker ingredients are uniformly distributed and will dissolve in the gastrointestinal tract and be available for absorption. No assumption is made that the marker or index compound selected for demonstration of dissolution is responsible for the purported effect. The test is valuable in that it assures that the formulation technology used is reflective of the state-of-the-art technology, provides a means to evaluate lot-to-lot performance over a product s shelf-life and that excipients used to facilitate transfer of the index or marker ingredients of the botanical to the human system are appropriate. 

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