Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 37
Filtrar
1.
J Chromatogr A ; 852(2): 525-34, 1999 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-10481989

RESUMO

Achiral and chiral interactions of alkyl nitrates (R-O-NO2) with heptakis-(3-O-acetyl-2,6-di-O-pentyl)-beta-cyclodextrin (LIPODEX-D) in the gas phase were investigated chromatographically. Two major outcomes can be summarized. First, LIPODEX-D shows very fast temperature-dependent variations of the selectivity up to changes in the order of elution for C1-C5 alkyl nitrates. These changes in selectivity reveal that LIPODEX-D possesses different shape selectivities for small alkyl nitrates at different temperatures (40-80 degrees C), i.e. with increasing isothermal separation temperature extended (chain-like) alkyl nitrates have increased retention relative to bulky alkyl nitrates. The observations are highly reproducible and might indicate conformational changes of the cyclodextrin, however, an ultimate proof would require further spectroscopic investigation. Secondly, the chiral separations of systematically varied sets of C4-C11 alkyl nitrates allowed the thermodynamic characterization of enantiodiscriminating interactions. Quantitative evidence is provided showing that the presence of an ethyl group at the asymmetric carbon atom of an n-alkyl nitrate gives a strong enthalpic contribution to the resulting enantioselectivity. The Gibbs free energy differences -deltaR,S(deltaG) decrease systematically three to six times if the ethyl group is either shortened or enlarged by only a -CH2-increment. The results are based on two separate thermodynamic approaches, i.e. the determination of thermodynamic quantities (-deltaR,S(deltaG), -deltaR,S(deltaH), -deltaR,S(deltaS), Tiso) and a theoretical concept of enthalpy-entropy compensation. The data from our laboratory experiments also indicate that van der Waals interactions are responsible for chiral discrimination.


Assuntos
Cromatografia Gasosa/métodos , Ciclodextrinas/química , Nitritos/química , beta-Ciclodextrinas , Sondas Moleculares , Estereoisomerismo , Termodinâmica
2.
Anal Bioanal Chem ; 356(1): 98-9, 1996 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-15048376

RESUMO

Cyclodextrins as cyclic hexa-(alpha) to octa-(gamma) saccharides are widely and successfully used after esterification or etherification as stationary phases in gas chromatography for the separation of chiral compounds. Their basic potential as thermostable stationary phases as such or after derivatisation offers a unique spectrum of interactions ranging from hydrogen bonding to shape selectivity. Similar properties as thermostable stationary phases are shown by long-chain saccharide ethers (chain-length C8-C20), which are normally used as non-ionic detergents.

3.
Anal Bioanal Chem ; 354(3): 333-43, 1996 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-15048459

RESUMO

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m(3) per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.

4.
Chemosphere ; 34(5-7): 1285-96, 1997.
Artigo em Inglês | MEDLINE | ID: mdl-9134673

RESUMO

Blubber tissues of the following marine mammals differing in their geographic distribution (North Atlantic, North Pacific, Bering Sea/Arctic Ocean), trophic level, and feeding habits were analyzed for their organochlorine contents: two seal species (harbor seals--Phoca vitulina, northern fur seals--Callorhinus ursinus), three toothed whale species (belukha whales--Delphinapterus leucas, one common dolphin--Delphinus delphis, one pilot whale--Globicephala melaena), and one baleen whale species (a bowhead whale--Balaena mysticetus). As xenobiotics were quantified the seven indicator congeners of the polychlorinated biphenyls (PCB 28, 52, 101, 118, 138, 153, and 180), three isomers of the hexachlorocyclohexanes (alpha-, beta- and gamma-HCH) as well as six components of the DDT-group (4,4'-DDT, 4,4'-DDD, 4,4'-DDE, 2,4'-DDT, 2,4'-DDD, and 2,4'-DDE). When comparing the xenobiotic levels of these marine mammals, it showed that the animals from the western North Atlantic were contaminated about 15 times more with organochlorines than the animals from the eastern North Pacific and the Bering Sea/Arctic Ocean. The total organochlorine burden, the 4,4'-DDE-percentage as well as the metabolic PCB patterns correlate with the trophic levels of the marine mammals studied. The quantitative analyses were done by high-resolution capillary gas chromatography with electron capture detection (HRGC/ECD) whereas the analyses of the metabolic PCB patterns were done by high-resolution capillary gas chromatography and mass selective detection (HRGC/MSD).


Assuntos
Golfinhos , Inseticidas/análise , Resíduos de Praguicidas/análise , Focas Verdadeiras , Poluentes Químicos da Água/análise , Baleias , Tecido Adiposo/química , Animais , Oceanos e Mares , Bifenilos Policlorados/análise
5.
Chemosphere ; 37(13): 2599-615, 1998 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-9839394

RESUMO

Alkyl nitrates with a chain length up to five carbon atoms have been determined in snow, white frost, and surface water. The samples were taken in the vicinity of Ulm, Germany, a region in central Europe. The determination of C1-C5-alkyl nitrates in water samples was achieved with a new water codistillation enrichment technique directly coupled with on-column head-space gas chromatography. The concentrations of the short chain alkyl nitrates in the different forms of wet deposition range from 89 ng L-1 for 1-propyl nitrate down to 35 ng L-1 for 1-pentyl nitrate. C1-C5-alkyl nitrates in wet depositions were also directly determined by static head-space gas chromatography. Gas-water partition coefficients KGW (Henry's law constant H) were determined by head-space gas chromatography and secondly by calculating the Henry's law constant by the ratio of vapor pressure to water solubility. The gas-water partition constants (dimensionless) or Henry's law constants range from KGW = 0.038 (H = 93 Pa m3 mol-1) for 1-propyl nitrate up to KGW = 0.122 (H = 302 Pa m3 mol-1) for 2-pentyl nitrate.


Assuntos
Água Doce/análise , Nitratos/análise , Poluentes Químicos da Água/análise , Abastecimento de Água/análise , Cromatografia Gasosa , Chuva , Neve
6.
Chemosphere ; 40(6): 651-60, 2000 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-10705541

RESUMO

The understanding of the global environmental multiphase distribution of persistent organic pollutants (POPs) as a result of the physico-chemical properties of the respective compounds is well established. We have analysed the results of a vertical transport of POPs from upper water layers (0-200 m) to the deepwater region (> 800 m) in terms of the contamination of the biophase in both water layers. The contents of persistent organochlorine compounds like polychlorinated biphenyls (PCBs) in fish living in the upper water layers of the North Atlantic and the South Atlantic, and at the continental shelf of California (Marine Sanctuary Monterey Bay and its deep-sea Canyon) are compared to the levels in deep-sea or bottom dwelling fish within the same geographic area. The deep-sea biota show significantly higher burdens as compared to surface-living species of the same region. There are also indications for recycling processes of POPs--in this case the PCBs--in the biophase of the abyss as well. It can be concluded that the bio- and geo phase of the deep-sea may act similarly as the upper horizons of forest and grasslands on the continents as an ultimate global sink for POPs in the marine environment.


Assuntos
Peixes , Bifenilos Policlorados/análise , Poluentes Químicos da Água/análise , Animais , Oceano Atlântico , California , Ecossistema , Monitoramento Ambiental/métodos
7.
Chemosphere ; 40(6): 661-70, 2000 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-10705542

RESUMO

The understanding of the global environmental multiphase distribution of persistent organic pollutants (POPs) as a result of the physico-chemical properties of the respective compounds is well established. We have analysed the results of a vertical transport of POPs from surface water to deepwater in terms of the contamination of the biota living in the respective environmental compartments. Samples were taken from the North and the South Atlantic and from the uprising water region of the continental shelf of California (Marine Sanctuary Monterey Bay and its Canyon). The contents of persistent organochlorine pesticides (DDTs, chlordanes, toxaphenes, HCHs, and HCB) in surface-living fish are compared to those in deepwater fish of the same geographic area. The deepwater biota show significantly higher burdens as compared to surface-living species of the same region. There are also indications for recycling processes of POPs of the class of organochlorine pesticides in the biophase of the abyss as well. It can be concluded that the bio- and geophase of the deep-sea may act as an ultimate global sink for persistent semivolatile contaminants in the marine environment like the soil on the continents.


Assuntos
Peixes , Hidrocarbonetos Clorados/análise , Praguicidas/análise , Poluentes Químicos da Água/análise , Animais , Oceano Atlântico , California , DDT/análise , Ecossistema , Monitoramento Ambiental
8.
Chemosphere ; 33(7): 1369-90, 1996 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-8799997

RESUMO

Three laboratories participated in an interlaboratory comparison exercise for the determination of polychlorinated biphenyl (PCB) congeners and chlorinated pesticides in Standard Reference Material (SRM) 1588 (Organics in Cod Liver Oil) a whale blubber control material, and six beluga whale (Delphinapterus leucas) blubber samples. The results are generally in good agreement. The minor disagreement of some of the results may be attributed to differences in detector calibrations, differences in chromatographic separation selectivity for specific compounds, or both. The SRM and control material help to validate the analytical procedures and to verify that these procedures remain in control.


Assuntos
Tecido Adiposo/química , Inseticidas/análise , Bifenilos Policlorados/análise , Baleias , Animais , Cromatografia Gasosa-Espectrometria de Massas , Variações Dependentes do Observador , Padrões de Referência
15.
Fresenius J Anal Chem ; 371(6): 882-90, 2001 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-11768481

RESUMO

The main components of five technical mixtures of brominated flame retardants were identified by mass spectroscopy, H-NMR, IR spectroscopy, elementary analysis, and HRGC-MS, respectively. The mixtures have been identified as: phosphoric acid bromopropylates: Bromcal P 67-6 HP; C18-alkylated bromophenols: Bromcal P 40-3; dibromopropyl-2,4,6-tribromophenyl ether: Bromcal 73-5 PE; brominated diphenyl ethers (PBrDE): Bromcal 70-5 DE; decabromodiphenyl ether: Bromcal 82-0. Gas chromatographic retention data of the various constituents were measured on standard GC columns. The data prove the interference of some of the brominated compounds with PCBs and other halogenated pesticides in HRGC using the electron capture detector.

16.
Fresenius J Anal Chem ; 366(4): 346-50, 2000 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-11220316

RESUMO

The synthesis of a beta-cyclodextrin-silica normal-phase (NP)-liquid chromatography (LC) stationary phase is reported. Silica gel was modified with (3-bromopropyl)trimethoxysilane to a 3-bromopropyl-silica that was reacted with beta-cyclodextrin, resulting in a beta-cyclodextrin-silica. To prove its usefulness in group-separation of organic nitrates among others, a mixture of three groups of organic nitrates was separated. The results are compared with those obtained on a nitrated polyol-silica that has recently been reported. The alkyl dinitrates exhibt higher retention relatively to alkyl mononitrates on the new phase. This allows to cut the LC fractions in a way that the alkyl mononitrates and phenylalkyl nitrates appear in one fraction and the dinitrates in a second one without any overlap of the two fractions.

17.
Fresenius J Anal Chem ; 366(4): 365-7, 2000 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-11220320

RESUMO

Patterns of volatile ECD-active substances in marine air at the ultra trace level were investigated. The protocol used carbon based adsorbents, thermodesorption and thick film HRGC-ECD together with a second ECD in line with oxygen doped make-up gas. The latter ECD mode leads to an increased sensitivity for chloromethane. dichloromethane, and other important chlorinated substances with an otherwise low response at an ECD driven with oxygen-free nitrogen or argon/methane. The experimental set-up is easily to employ. Air samples were taken on two cruises of the German research vessel R/V "Polarstem" in the Atlantic Ocean to determine the background pattern of all volatile halocarbons from CF3Cl to CHI3 in marine air.


Assuntos
Atmosfera/química , Clorofluorcarbonetos/análise , Cloreto de Metila/análise , Cloreto de Metileno/análise , Oceano Atlântico , Efeito Estufa , Hidrocarbonetos Iodados/análise , Ozônio , Sensibilidade e Especificidade
18.
Int J Environ Anal Chem ; 8(1): 15-35, 1980.
Artigo em Inglês | MEDLINE | ID: mdl-7399798

RESUMO

Pristine Alpian fresh water lakes with no run off were selected to monitor the atmospheric fall-out of C6--C12 -organochlorine compounds. Off-shore marine areas were taken for monitoring the average marine pollution by these compounds. In both cases fishes have been used as bioextractors. The analytical work-up combines solvent-partition, liquid chromatography and glass capillary gas chromatography with the electron capture detector. The idenfification is done by matching high-resilution retention indices of unknowns with those of reference compounds. The following compounds could be identified in the spawn of arctic chars (Salvelinus alpinus) caught in off-road Alpian lakes as well as in the liver of predatory antarctic cod (Dissostichus eleginoides) caught near South Georgia, as well as in Peru fish oil and crude sperm oil: hexachlorobenzene alpha-, beta-, gamma-hexachlorocyclohexane; 4,4'-DDT; 4,4'-DDE; 4,4'-DDD; 2,4'-DDE; 2,4'-DDD; heptachloroepoxide; polychlorobiphenyls (PCB) and polychlorocamphenes. Concentrations are given in nanogram/gram total lipid extract (ppb). First value Salvelinus (Alps), second value Dissostich (Antarctic Ocean), alpha-HCH: 40/0,1; beta-HCH: 4,1/0,1; gamma-HCH: 17,2/0,1; HCB: 65/8; 4,4'-DDT: 59/4; 4,4'-DDE: 477/5; sigma DDT 646/11,4; sigma PCB: 1030/32; sigma PCC: 124/68.


Assuntos
Hidrocarbonetos Halogenados/análise , Poluentes Químicos da Água/análise , Poluentes da Água/análise , Poluentes Atmosféricos , Animais , Regiões Antárticas , Cromatografia Gasosa , Europa (Continente) , Peixes/metabolismo , Óleos/análise
19.
Fresenius J Anal Chem ; 368(2-3): 244-9, 2000.
Artigo em Inglês | MEDLINE | ID: mdl-11220587

RESUMO

Air samples of the atmospheric ground layer in the cities of Ulm in Germany, Las Vegas, Nevada, and Salt Lake City, Utah, in the US were analyzed for organic nitrates. The air samples were taken around noon in summer at sunny weather conditions. 43 (C6-C13) alkyl mononitrates, 24 (C3-C6) alkyl dinitrates, and 19 (C2-C6) hydroxy alkyl nitrates have been identified. The analytical protocol included high-volume-sampling, NP-HPLC group separation, high resolution capillary gas chromatography, and detection by the highly selective mass spectrometer detector (SIM mode, m/z = 46). The levels of the sum of 15 (C6-C10) alkyl mononitrates ranged from 2.9 to 11.0 parts per trillion (ppt(v)). The levels of the sum of 21 (C3-C6) alkyl dinitrates ranged from 2.3 to 10.5 ppt(v), and the levels of the sum of 7 (C2-C4) hydroxy alkyl nitrates ranged from 7.3 to 28 ppt(v), respectively, in the urban air samples. These results emphazise the contribution of the alkyl dinitrates and hydroxy alkyl nitrates besides the alkyl mononitrates to the budget of NO(Y) compounds. No major differences in levels and pattern of the organic nitrates are present in air of the German and the US cities.

20.
Fresenius J Anal Chem ; 371(5): 598-606, 2001 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-11767885

RESUMO

Halogenated methyl-phenyl ethers (methoxybenzenes, anisoles) are ubiquitous organics in the environment although they are not produced in industrial quantities. Modelling the fate of organic pollutants such as halogenated anisoles requires a knowledge of the fundamental physico-chemical properties of these compounds. The isomer-specific separation and detection of 60 of the 134 possible congeners allowing an environmental fingerprinting are reported in this study. The vapor pressure p0(L) of more than 60 and further physico-chemical properties of 26 available congeners are given. Vapor pressures p0(L), water solubilities S(L)W, and n-octanol/water partition coefficients Kow were determined by capillary HR-GC (High Resolution Gas Chromatography) on a non-polar phase and by RP-HPLC (Reversed Phase High Performance Liquid Chromatography) on a C18 phase with chlorobenzenes as reference standards. From these experimental data the Henry's law constants H, and the gas/water Kgw and gas/n-octanol Kgo partition coefficients were calculated. We found that vapor pressures, water solubilities, and n-octanol/water partition coefficients of the halogenated anisoles are close to those of the chlorobenzenes. A similar environmental fate of both groups can, therefore, be predicted.


Assuntos
Anisóis/análise , Poluentes Ambientais/análise , Hidrocarbonetos Halogenados/análise , Modelos Químicos , Anisóis/química , Cromatografia Líquida de Alta Pressão , Cromatografia Gasosa-Espectrometria de Massas , Hidrocarbonetos Halogenados/química , Solubilidade
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA