Determination isomer specific

Additional 14C-tracer studies were conducted to determine the specific isomer participation for TeNMe formation. In the dinitration mixt there are six isomers present 2,4-, 2,6-, 2,3-, 2,5-, 3,4- and 3,5-Dinitrotoluene (DNT). It was observed that 83% of the TeNMe formed from carbon-1 came from the DNT isomers derived from m-Nitrotoluene. The relative participation of DNT isomers for TeNMe formation is summarized in Table 1... 

For details of the clean-up of the pyrolysate of the DIN oven see reference 12. Identification and quantification of PBDD/F was performed by GC/MS (refs. 8-12). This was done for all brominated PBDD and PBDF from mono- through octabromo compounds using external standards which were either prepared (refs. 11-13) or purchased. There exists a total of 210 brominated compounds of PBDD/F. Since not all isomers are available a complete isomer-specific determination could not be performed. 

LC-MS or LC-MS-MS using ESI or APCI are versatile tools for the isomer-specific determination of trace levels of HBCDs, monitoring the specific transitions mlz 640.6 to mlz 78.9 and 80.9. Budakowsky and Tomy [117] showed that APCI has lower intensities than in a similar experiment with ESI. Consequently, the ESI mode was preferred for determining diastereoisomers in several studies. Different methods for the analysis of diastereoisomeric HBCD using LC-ESI-MS-MS and SRM were developed, obtaining LODs of 0.5-6 pg on-column [117, 118]. 

All amino acids except glycine exist in these two different isomeric forms but only the L isomers of the a-amino acids are found in proteins, although many D amino acids do occur naturally, for example in certain bacterial cell walls and polypeptide antibiotics. It is difficult to differentiate between the D and the L isomers by chemical methods and when it is necessary to resolve a racemic mixture, an isomer-specific enzyme provides a convenient way to degrade the unwanted isomer, leaving the other isomer intact. Similarly in a particular sample, one isomer may be determined in the presence of the other using an enzyme with a specificity for the isomer under investigation. The other isomer present will not act as a substrate for the enzyme and no enzymic activity will be demonstrated. The enzyme L-amino acid oxidase (EC 1.4.3.2), for example, is an enzyme that shows activity only with L amino acids and will not react with the D amino acids. 

Analytical model, assumptions and practical implications, 52-57 Analytical performance, correlation chromatography, 108 Analytical process, steps of, 7 Aroclors, isomer-specific analysis of, application of SIMCA, 195-232 Atomic absorption spectrometry, determination of iron in water, 116... 

For example, a single estimate for total PCB s has been historically collected in the NHATS program. Current advances in chemical analysis protocols now allow for the determination of isomer specific resolution of PCB s. Given the 209 PCB s that are now possible to detect, an adequate evaluation of the data without the use of pattern recognition techniques seems impossible. From a QA/QC perspective, these methods can facilitate the detection of outliers and aid in the interpretation of human chemical residue data. The application of statistical analysis must keep abreast with these advances made in chemisty. To handle the complexity and quantity of such data, the use of more sophisticated statistical analyses is needed. 

An analytical chemical technique that utilizes radioactive (or stable) isotopes for the quantitative analysis of the amount of substance. In the absence of a kinetic isotope effect, isotopic isomers react identically with respect to their unlabeled counterparts. The method offers the advantage that specific activity (or gram-atom excess in the case of stable isotopes) is an intensive variable. Therefore, one only needs to recover sufficient labeled metabolite to determine amount of substance and disintegrations per minute (or, gram-atom excess) to reach an accurate determination of specific activity. The technique is feasible so long as one can accurately determine the initial and final specific activities. 

Loganathan BG, Kannn K, Watanabe, et al. 1995. Isomer-specific determination and toxic evaluation of polychlrinated biphenyls, polychlorinated/brominated dibenzo-p-dioxins and dibenzofurans, polybrominated biphenyl ethers, and extractable organic halogen in carp from the Buffalo River, New York. Environ Sci Technol 29(7) 1832-1838. 

For the quantitative determination of polychlorinated diben-zodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), sample treatment and conservation play crucial roles, too. Only some of the 75 PCDD isomers and 135 PCDF isomers are highly toxic. The collection and analysis of the hazardous compounds present at ultratrace levels in environmental samples must preferably be isomer-specific. The exposure routes for these compounds originate from combustion processes (18-19). 

Wakimoto, T., Kannan, N., Ono, M., Tatsukawa, R., Masuda, Y., 1988. Isomer-specific determination of polychlorinated dibenzofurans in Japanese and American Polychlorinated biphenyls. Chemosphere 17, 743-750. 

Beck H, Eckart K, Mathar W, et al. 1988a. Isomer-specific determination of... 

Forst C, Stieglitz L, Zwick G. 1988. Isomer-specific determination of PCDD/PCDF in oil extracts from water leachate of a waste landfill. Chemosphere 17 1935-1944. 

Neidhard H (1990), Vortrag auf dem GDCh Info-Tag 49619. Das internationale System der toxi-schen Aquivalente und Bewertung von Quellen", Frankfurt, 09.03.1990 Nestrick TJ, Lamparski LL (1982), Anal. Chem. 54 2292-2299. Isomer-specific determination of chlorinated dioxins for assessment of formation and potential environmental emission from wood combustion"... 

Miles WF, Gurprasad NP, Malis GP (1985), Anal. Chem. 57 1133-1138. Isomer-specific determination of hexachlorodibenzo-p-dioxins by oxygen negative chemical ionization mass spectrometry, gas chromatography, and high-pressure liquid chromatography"... 

Handbook of Chemistry and Physics" (1983), 63. Edition, CRC Press, Boca Raton Kurz J, Ballschmiter K (1995), Fresenius J. Anal. Chem. 351 98-109. Isomer-specific determination of 79 polychlorinated diphenyl ethers (PCDE) in cod liver oils, chlorophenols and in a fly ash" Nestrick TJ, Lamparski LL, Crummett WB (1987), Chemosphere 16 777-790. Thermolytic surface reaction of benzene and iron(III) chloride to form chlorinated dibenzo-p-dioxins and dibenzofurans"... 

Thielen DR, Olsen G (1988), Anal. Chem. 60 1332-1336.. .Optimization of alumina selectivity for tetrachlorodibenzo-p-dioxins and the isomer-specific determination of 2,3,7,8-tetrachloro-dibenzo-p-dioxin ... 

Oehme M, Kirschmer P (1984), Anal. Chem. 56 2754-2759. Isomer-specific determination of tetrachlorodibenzo-p-dioxins using hydroxyl negative ion chemical ionization mass spectrometry combines with high-resolution gas chromatography"... 

Isomer specificity for all 2,3,7,8-substituted PCDDs/PCDFs cannot be achieved on the 60 m DB-5 column. In order to determine the concentration of the individual 2,3,7,8-substituted isomers, if the toxicity equivalence is greater than 0.7 ppb (solids), 7 ppt (aqueous), or 7 ppb (chemical waste), the sample extract shall be reanalyzed on a 60 m SP-2330 or SP-2331 (or equivalent) GC column. 

These substitution reactions proceed cleanly and give only trace amounts of side products unless the reactions are carried out under forcing conditions. With the aid of - -H and 31p nmr spectroscopy, we have been able to take advantage of the low symmetry of these derivatives and determine the specific sites at which substitution occurs in H2FeRu3(C0)33. Figure 1, for example, shows the 1h NMR spectrum of H2FeRu3(CO)(PM Ph) at -50°C which indicates the presence of two substitutional isomers for the compound. The intense doublet at t 28.07 ppm... 

A professor once received from a chemical supply house a specimen of a crystalline organic compound needed in her research. This compound was optically active, with a positive rotation (i.e., it was dextrorotatory). The professor wanted to check that the sample was not contaminated by the other (levorotatory) optical isomer. Such contamination would decrease the magnitude of the positive rotation. Therefore she gave a small amount of the material to a graduate student with instructions to determine its specific rotation at 25°C with the highly precise polarimeter available in the laboratory (see Exp. 28 and Chapter XIX). 

Isobe, T., Ramu, K., Kajiwara, N., Takahasbi, S., Lam, P. K. S., Jefferson, T. A., Zbou, K., Tanabe, S. (2007) Isomer specific determination of bexabromocyclododecanes (HBCDs) in small cretaceans from the South China Sea - levels and temporal variation. Mar. Pollut. Bull, 54 1139-1145. 

NICI mass spectra do not contain isomer-specific information. Therefore, this technique is most suitable for the determination of molecular mass information and quantification (see Sect. 3.3.1.1). 

Normal-phase HPLC, using an amino-bonded phase, was used for determination of the PAHs of up to 7 rings. This type of separation results in elution by the number of n bonds. A special reversed-phase octadecyl column was used for PAHs of 7 through 12 rings. This HPLC packing, Vydac 201TP5, is well known for its orderly structure and separates the PAHs by their overall shapes. It has been compared to the liquid-crystal phases used in gas chromatography. It provides the best isomer specific separation of PAHs. 

Quantification was based upon the method generally referred to as internal standardisation using, within each isomeric group, one C-labelled isomer as an internal standard. Inevitable differences in chromatographic retention and/or minor differences in ionisation efficiency, mass spectrometric fragmentation and ion masses monitored, lead to differences in sensitivities between the compounds to be determined and the corresponding C-labelled internal standards. These effects were accounted for in the final concentration calculation by the introduction of isomer specific relative sensitivity factors (RSF). Additional details on this procedure are described elsewhere [18,19]. 

Those that indicated accidental exposure were 2,4,4 triCB, 2 3,4-triCB, and 2,3 4-,4 tetraCB (Luotamo et al. 1993). Thus, it would appear that in some cases isomer-specific monitoring of serum levels of PCB congeners in humans can determine likely exposure soitrces (Luotamo 1988). 

Tanabe S, Kannan N, Wakimoto T, et al. 1989. Isomer-specific determination and toxic evaluation of potentially hazardous coplanar PCBs, dibenzofurans and dioxins in the tissues of "Yusho" PCB poisoning victim and in the causal oil. Toxicol Environ Chem 24 215-231. 

Ehmann J, Ballschmitter K (1989) Isomer-specific determination of tetrachlorobenzyltoluenes (TCBT) in the technical mixture Ugilec 141 by capillary gas chromatography. Fresenius J Anal Chem 332, 904-911. 

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