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Paper des Monats
- ja (1)
A method for the determination of the novel brominated flame retardant tetrabromobisphenol A bis(2,3-dibromopropylether), 1,1'-(isopropylidene)bis[3,5-dibromo-4-(2,3-dibromo-propoxy)-benzene] (TBBPA-dbpe), was developed. Technical TBBPA-dbpe was purified and the results of a thorough physical characterisation are reported. The application of APCI-MS is discussed and the fragmentation patterns are described. Quantification of TBBPA-dbpe was done by HPLC-DAD using external calibration. The validation of the method was accomplished using sediment and sewage sludge samples spiked with defined amounts of authentic TBBPA-dbpe. The average recovery rates of TBBPA-dbpe from spiked samples ranged from 35 to 91% (sediment) and from 57 to 98% (sewage sludge) depending on the respective extraction method. Pressurised fluid extraction (PFE) and fluidised bed extraction were superior to classical Soxhlet and sonication procedures and yielded recovery rates between 90 and 98% with relative standard deviations of 2%. The limits of detection (DTC), identification (ID) and determination (DTM) using HPLC-DAD were 10, 21 and 30 ng g-1 in sediment and 22, 44 and 72 ng g-1 in sewage sludge, respectively.
Arsenolipids represent a relevant step in the biosynthesis of organoarsenicals from inorganic arsenic compounds. Their fate after human consumption is still uncertain.
By means of a HPLC-ICP-MS/ESI-Q-TOF-MS method, 16 lipid soluble arsenic compounds, including seven formerly unknown organoarsenicals, have been identified in commercial herring fillet.
The structural assignment was done by exact mass and high resolution MS/MS data. This is the first identification of arsenolipids in herring (Clupea harengus). They contribute with (3.6±0.2) mg kg-1 arsenic to 62.3% of the total arsenic content of (5.7±0.3) mg of arsenic per kg dry mass. Current studies indicate that a metabolization by humans to cancerous dimethylarsinic acid is very likely. The presented results are highly relevant as herring is a very popular food fish species in Europe. Moreover, the screening of different fish species revealed that arsenolipids are more widespread than previously assumed.
A procedure has been developed for the determination of arsenobetaine in fish matrix by HPLC–ESI-MS/MS. Hereby (trimethylarsonium)-1,2-13C-acetate (arsenobetaine) is used as internal calibration standard. Arsenobetaine was determined in a fish material (Sea Bass) with an expanded uncertainty of 3.8%.
The reaction pathways of amino acids and reducing sugars are now fully understood. The focus in the last few years, however, has turned to the reaction of peptides and proteins with reducing sugars. We have investigated the reaction of γ-aminobutanoic acid, the heptapeptide Nα-Acetyl-Lys-Lys-β-Ala-Lys-β-Ala-Lys-Gly, and the model protein β-casein in Maillard reactions with 1-13C arabinose. Characterization of 13C-labeled acetic acid and norfuraneol by gas chromatographymass spectrometry and nuclear magnetic resonance revealed new formation pathways. The results demonstrate significant differences in the labeling pattern of the products depending on the amine used, indicating different formation pathways of acetic acid and norfuraneol.
Hands-off linear interaction energy approach to binding mode and affinity estimation of estrogens
(2013)
With this work we target the development of a predictictive model for the identification of small molecules which bind to the estrogen receptor alpha and, thus, may act as endocrine disruptors. We propose a combined thermodynamic approach for the estimation of preferential binding modes along with corresponding free energy differences using a linear interaction energy (LIE) ansatz. The LIE model is extended by a Monte Carlo approach for the computation of conformational entropies as recently developed by our group. Incorporating the entropy contribution substantially increased the correlation with experimental affinity values. Both squared coefficients for the fitted data as well as the more meaningful leave-one-out cross-validation of predicted energies were elevated up to rFit2 = 0.87 and qLOO2 = 0.82, respectively. All calculations have been performed on a set of 31 highly diverse ligands regarding their structural properties and affinities to the estrogen receptor alpha. Comparison of predicted ligand orientations with crystallographic data retrieved from the Protein database pdb.org revealed remarkable binding mode predictions.
The derivatization of organoarsenic compounds by different reagents like thioglycolates or dithiols and the subsequent analysis by GC–MS as a molecular specific technique was investigated and described. The possible derivatization reagents methyl- and ethylthioglycolate (TGM and TGE), 1,3-propane- and 1,5-pentanedithiol (PDT and PeDT), which transfer the polar and nonvolatile analytes dimethylarsenate (DMA), monomethylarsonate (MMA), arsenite and arsenate into volatile compounds, were evaluated. The application for real samples like fish material was also studied.
In addition the gas chromatographic separation and resolution was optimized and experiments were carried out to determine the highest derivatization rates. Derivatization reagents were evaluated in terms of quantity and stability of the formed chemical species.
All derivatization products were characterized by mass spectrometry in order to identify the separated arsenic species.
The most efficient conversion of DMA and MMA was observed by using ethylthioglycolate as derivatization agent. Finally, the derivatization procedure and the GC–MS-method were validated to determine linearity, precision, selectivity, analytical limiting values and recoveries. For the proposed method a limit of detection (LOD) of 5.8 pg for DMA and 14.0 pg for MMA was found. The accuracy was established by comparing the mean value measured for DMA in the certified reference material BCR-627 (tuna fish) with the certified one.
MMA was not quantified in marine samples due to its low content. In shrimp samples DMA was not detectable. For codfish a DMA-content of 0.20±0.004 mg kg-1, for 'Surströmming' an amount of 0.38±0.02 mg kg-1 and for herring, which showed the highest amount of DMA, a content of 1.15±0.03 mg kg-1 was determined.
The chemical analysis of fire debris represents a crucial part in fire investigations to determine the cause of a fire. A headspace solid-phase microextraction (HS-SPME) procedure for the detection of ignitable liquids in fire debris using a fiber coated with a mixture of three different sorbent materials (Divinylbenzene/Carboxen/Polydimethylsiloxane, DVB/CAR/PDMS) is described. Gasoline and diesel fuel were spiked upon a preburnt matrix (wood charcoal), extracted and concentrated with HS-SPME and then analyzed with gas chromatography/mass spectrometry (GC/MS). The experimental conditions—extraction temperature, incubation and exposure time—were optimized. To assess the applicability of the method, fire debris samples were prepared in the smoke density chamber (SDC) and a controlled-atmosphere cone calorimeter. The developed methods were successfully applied to burnt particleboard and carpet samples. The results demonstrate that the procedure that has been developed here is suitable for detecting these ignitable liquids in highly burnt debris.
The present study was focused on the determination and identification of arsenic species in methanolic extracts of cod liver. Arsenic species were fractionated and the fractions analysed by RP-HPLC-ICP-MS coupled with ESI-Q-TOF-MS. The total concentration of arsenic in the fresh cod liver was analysed by ICP-MS to be 1.53 ± 0.02 mg As kg-1 w.w. and the extraction recovery was ca. 100% and the column recovery >93%. Besides polar inorganic and methylated arsenic species (>70%) more hydrophobic arsenic-containing fatty acids and hydrocarbons occurred. Based on the mass spectrometric data proposals for molecular structures were elaborated for 20 of the organic As species included 10 arsenic-containing fatty acids (AsFA) and an arsenic-containing hydrocarbon (AsHC) mentioned for the first time in fresh cod liver. Arsenobetaine was found as main water-soluble arsenic compound in cod liver followed by higher molecular mass arsenic-containing fatty acids and hydrocarbons.
A recently introduced inductively coupled plasma-time-of-flight-mass spectrometer (ICP-ToF-MS) shows enhanced sensitivity compared to previous developments and superior isotope ratio precision compared to other ToF and commonly used single-collector ICP-MS instruments. Following this fact, an improvement for isotope dilution ICP-MS using the new instrumentation has been reported. This study aimed at investigating whether this improvement also meets the requirements of species-specific isotope dilution using GC/ICP-MS, where short transient signals are recorded. The results of the analysis of monomethylmercury (MMHg) of a sediment reference material show that isotope ratio precision of ICP-MS instruments equipped with quadrupole, sector-field, and time-of-flight mass analyzers is similar within a broad range of peak signal-to-noise ratio when analyzing one isotopic system. The procedural limit of quantification (LOQ) for MMHg, expressed as mass fraction of Hg being present as MMHg, w(Hg)MMHg, was similar as well for all investigated instruments and ranged between 0.003 and 0.016 μg/kg. Due to the simultaneous detection capability, the ICP-ToF-MS might, however, be more favorable when several isotopic systems are analyzed within one measurement. In a case study, the GC/ICP-ToF-MS coupling was applied for analysis of MMHg in sediments of Finow Canal, a historic German canal heavily polluted with mercury. Mass fractions between 0.180 and 41 μg/kg (w(Hg)MMHg) for MMHg, and 0.056 and 126 mg/kg (w(Hg)total) for total mercury were found in sediment samples taken from the canal upstream and downstream of a former chemical plant.