Biomedical subjects

U A Th Brinkman

Publications and source records attributed to U A Th Brinkman.

18 recordsLinked to original sources

PubMed2005

Comprehensive two-dimensional gas chromatography of polybrominated diphenyl ethers.

Comprehensive two-dimensional gas chromatography with micro electron-capture detection (GCxGC-muECD) was evaluated for the separation of 125 polybrominated diphenyl ethers (PBDEs). From among the six column combinations that were evaluated, DB-1x007-65HT was found to be the most suitable because of: (i) the highest number of BDE congeners separated; (ii) the least decomposition of higher brominated congeners; and (iii) the most suitable maximum operating temperature. The separation of the 125 BDE congeners from five hydroxy- and two methoxy-BDEs and nine other brominated flame retardants (polybrominated biphenyls, tetrabromobisphenol-A, methyl-tetrabromobisphenol-A and hexabromocyclododecane) was also studied. Fluorinated BDEs were found to be valuable internal standards for the determination of BDEs because of their very similar physico-chemical properties and excellent separation from the parent BDEs, mainly in the second dimension. GCxGC-time-of-flight MS and GCxGC-muECD were shown to be useful tools to identify decomposition products of nona- and deca-substituted BDEs, which are formed during the GC run. Three nona-BDEs were shown to be the major decomposition products of BDE 209.

Chromatography, Gas↗

PubMed2005

Characterization of polychlorinated n-alkanes using comprehensive two-dimensional gas chromatography--electron-capture negative ionisation time-of-flight mass spectrometry.

Comprehensive two-dimensional gas chromatography with electron-capture negative ionization time-of-flight mass spectrometry (GC x GC-ECNI-TOF-MS) is used to study the composition and characteristics of short-, medium- and long-chain polychlorinated n-alkane (PCA) mixtures. Distinct ordered structures, which enable the highlighting and interpretation of group and sub-group separations are observed when using a DB-1 x 007-65HT column combination. The analysis of a number of, mutually rather different, technical mixtures and 35 individual standard compounds provides information on the role of chlorine substitution (number of substituents as well as their position), the contribution of carbon versus chlorine atoms to analyte volatility, i.e. GC x GC behaviour, and the influence of the chain length of the carbon skeleton. Two dust samples are analyzed to illustrate the practical usefulness of the proposed procedure.

Alkanes↗

PubMed2005

Group separation of organohalogenated compounds by means of comprehensive two-dimensional gas chromatography.

Separations of 12 compound classes, polychlorinated biphenyls (PCBs), diphenyl ethers (PCDEs), naphthalenes (PCNs), dibenzothiophenes (PCDTs), dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), terphenyls (PCTs) and alkanes (PCAs), toxaphene, organohalogenated pesticides (OCPs), and polybrominated biphenyls (PBBs) and diphenyl ethers (PBDEs) by comprehensive two-dimensional gas chromatography were evaluated. Five column combinations, DB-1 x 007-210, DB-1 x HT-8, DB-1 x LC-50, DB-1 x 007-65HT and DB-1 x VF-23ms were used to study, primarily, group-type separations, but attention was devoted also to within-class separation, especially for those classes which were not addressed in much detail before, the PCNs, OCPs, PBBs and PCTs. The DB-1 x 007-210 column set did not offer any extra separation compared to one-dimensional GC. For the DB-1 x HT-8 column combination, the useful principle of congener separation on the basis of number of halogen substituents in a molecule was confirmed (PCBs, toxaphene) and extended (PCTs, PBDEs). No practically useful group-type separation was observed for this column combination. The DB-1 x LC-50 set provides group separation based on planarity: planar compounds such as PCDDs, PCDFs, PCDTs and PCNs are much more retained than, and therefore separated from, non-planar analytes. Within the classes of PCBs, PBBs and PCTs highly useful separation of planar from non-planar compounds was also observed. The DB-1 x 007-65HT column set effectively separates PCAs and PBDEs from all other compound classes, and provides a good separation of brominated and chlorinated analogue classes from each other. This column set was the most efficient one for within-class separation of OCPs and PCNs. Finally, DB-1 x VF-23ms yields excellent within-class separations, especially of non-aromatic compounds, viz. OCPs, toxaphene and PCAs. No group separation was observed here. The applicability of the approach was demonstrated for a sediment extract and a dust extract. In the sediment extract, PCDDs, PCDFs, PCAs and PCNs were identified and their efficient separation was achieved. In the dust sample, separation of PCAs and PBDEs was achieved and several new PBDE congeners were identified.

Chromatography, Gas↗

PubMed2005

Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography.

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC x GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC x GC-ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10-150 fg injected) and CDD/Fs (10-700 fg injected) in the selected ion monitoring mode.

Gas Chromatography-Mass Spectrometry↗

PubMed2005

Analytical strategies for residue analysis of veterinary drugs and growth-promoting agents in food-producing animals--a review.

After a brief introduction into the field of veterinary drugs and growth-promoting agents, the most important EU regulations and directives for the inspection of food-producing animals and animal products regarding the residue control of these substances are presented and discussed. Main attention in the review is on the methods of analysis in use today for the most important classes of veterinary drugs and growth-promoting agents viz. anthelmintics, antibiotics, coccidiostats, hormones, beta-agonists and tranquillizers. Emphasis is given to the potential, and limitations, of state-of-the-art analytical procedures and their performance characteristics. The most obvious conclusion is that, today (reversed-phase) liquid chromatography combined with tandem mass spectrometric detection--either triple-quadrupole or ion-trap multi-stage--is the preferred technique in a large majority of all cases. In the field of sample treatment, the combined use of liquid extraction--i.e., liquid partitioning or liquid-liquid extraction--and liquid-solid extraction--primary on- or off-line solid-phase extraction--is most popular. Finally, while the analytical tools required to meet the demands typically formulated by governments and international organizations today, generally speaking are available, several problems still do exist. To quote three examples, problems are encountered in the area of simultaneously extracting and pre-treating groups of analytes with mutually widely different polarities, with regard to identification-point--based confirmation of analyte identity, and regarding quantification errors caused by ion-suppression effects. Improving the speed of analysis is another aspect that should, and will, receive dedicated interest in the near future.

Chromatography, Liquid↗

PubMed2004

Miniaturization in sample treatment for environmental analysis.

The increasing demand for faster, more cost-effective and environmentally friendly analytical methods is a major incentive to improve the classical procedures used for sample treatment in environmental analysis. In most classical procedures, the use of rapid and powerful instrumental techniques for the final separation and detection of the analytes contrasts with the time-consuming and usually manual methods used for sample preparation, which slows down the total analytical process. The efforts made in this field in the past ten years have led to the adaptation of existing methods and the development of new techniques to save time and chemicals, and improve overall performance. One route has been to develop at-line or on-line and, frequently, automated systems. In these approaches, miniaturization has been a key factor in designing integrated analytical systems to provide higher sample throughput and/or unattended operation. Selected examples of novel developments in the field of miniaturized sample preparation for environmental analysis are used to evaluate the merits of the various techniques on the basis of published data on real-life analyses of trace-level organic pollutants. Perspectives and trends are briefly discussed.

Journal Article↗

PubMed2004

Separation of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans and 12 dioxin-like polychlorinated biphenyls by comprehensive two-dimensional gas chromatography with electron-capture detection.

Comprehensive two-dimensional gas chromatography (GC x GC) with electron-capture detection (ECD) has been optimized for the separation of seventeen 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans and 12 dioxin-like polychlorinated biphenyls, with emphasis on the selection of the first- and second-dimension, commercially available, columns. When eight second-dimension columns were subsequently combined with a 100% methylpolysiloxane stationary phase (DB-1) in the first dimension to create orthogonal conditions, a complete separation of all congeners with different TEF values was obtained with two column combinations, DB-1 x VF-23 and DB-1 x LC-50. When other types of first-dimension columns were used (and orthogonality was partly sacrificed), a DB-XLB column combined with 007-65HT, VF-23 and LC-50 was found to provide a complete separation of all 29 priority congeners. Next, the potential of these three column combinations for real-life analysis was preliminarily studied. With a spiked and fractionated milk extract, DB-XLB x LC-50 was found to be the most powerful column combination, because of the good separation of the 29 priority congeners from each other as well as from the matrix constituents. Quantitative performance (close to three-order linearity; LODs, 30-150 fg injected; R.S.D.s, 1.5-6.5% (n = 10)) was satisfactory.

Benzofurans↗

PubMed2003

Hyphenation and hypernation the practice and prospects of multiple hyphenation.

In the past two decades, combining a chromatographic separation system on-line with a spectroscopic detector in order to obtain structural information on the analytes present in a sample has become the most important approach for the identification and/or confirmation of the identity of target and unknown chemical compounds. In most instances, such hyphenation can be accomplished by using commercially available equipment For most (trace-level) analytical problems encountered today, the combination of column liquid chromatography or capillary gas chromatography with a mass spectrometer (LC-MS and GC-MS, respectively) is the preferred approach. However, it is also true that additional and/or complementary information is, in quite a number of cases, urgently required. This can be provided by, for example, atomic emission, Fourier-transform infrared, diode-array UV-vis absorbance or fluorescence emission, or nuclear magnetic resonance spectrometry. In the present review, the various options are briefly discussed and a few relevant applications are quoted for each combination. Special attention is devoted to systems in which multiple hyphenation, or hypernation, is an integral part of the setup. As regards this topic, the relative merits of various combinations--which turn out to include a mass spectrometer as one of the detectors in essentially all cases--are discussed and the fundamental differences between GC- and LC-based systems are outlined. Finally, the practicability of more extensive hypernation in LC, viz. with up to four spectrometers, is discussed. It is demonstrated that, technically, such multiple hyphenation is possible and that, from a practical point of view, rewarding results can be obtained. In other words, further research in this area is certainly indicated. However, in the foreseeable future, using several separate conventional hyphenated systems will be the commonly implemented solution in most instances.

Chromatography, Gas↗

PubMed2003

Attempt to unravel the composition of toxaphene by comprehensive two-dimensional gas chromatography with selective detection.

Comprehensive two-dimensional gas chromatography (GC x GC) coupled with micro electron-capture and time-of-flight mass spectrometric (TOF-MS) detection has been used to analyse technical toxaphene. An HP-1 x HT-8 column combination yielded highly structured chromatograms and revealed a complex mixture of over 1000 compounds what is significantly higher number than in any study before. The analysis of a mixture of 23 individual congeners and TOF-MS evaluation of technical toxaphene showed that the chromatogram is structured according to the number of chlorine substituents in a molecule. The nature of the compounds (bornane and camphene) does not appear to have any influence. The sum of the peak areas of all congeners in each group was calculated using laboratory-written software; based on these results, the composition of technical toxaphene as a function of the number of chlorine substituents was provisionally calculated and was found that hepta- and octachlorinated compounds represents 75% of the total toxaphene area.

Chromatography, Gas↗

PubMed2003

Single-jet, single-stage cryogenic modulator for comprehensive two-dimensional gas chromatography (GC x GC).

A simple, single-stage CO2 jet modulator has been designed, which cools only a single, ca. 10 mm long section of the front part of the second-dimension column of a comprehensive two-dimensional gas chromatographic (GC x GC) system. Direct heating by means of the GC oven air effects remobilization of the small fractions trapped upon eluting from the first-dimension column within a predetermined short period of time. Evaluation of the present modulator for the GC x GC separation of (very) polar flavour as well as non-polar compounds shows that the analytical performance of the single-stage modulator is closely similar to that of earlier reported, more complex, types of modulator.

Food Analysis↗

PubMed2002

Current use of pressurised liquid extraction and subcritical water extraction in environmental analysis.

This review updates our knowledge about pressurised liquid extraction (PLE) and subcritical water extraction (SWE), two sample preparation techniques which are increasingly used for the extraction of moderately and non-volatile organic pollutants from a variety of solid and semi-solid environmental matrices. Parameters influencing the extraction yield and selectivity are discussed. The results deriving from the analysis of several different classes of compounds in a variety of matrices are compared with a reference method, e.g., Soxhlet extraction. PLE and SWE are both promising techniques due to the short extraction times and low solvent consumption. In addition, SWE offers a wide range of polarities by changing the temperature and can easily provide class-selective extraction by temperature programming and/or the addition of modifier(s). This indicates that, even though many applications have already been reported, more can be expected.

Environmental Monitoring↗

PubMed2002

Gas chromatographic methods for oil analysis.

In the past 50 years. gas chromatography (GC) has played a most important role in the analysis of oil. In this review, the early history is briefly reviewed; next developments in this highly relevant application area since about 1985 are highlighted. The main topic of interest are the introduction and decisive role of capillary GC, the use of selective detection techniques, the versatility of coupled-column techniques and, specifically, the additional power of comprehensive two-dimensional GC.

Chromatography, Gas↗

PubMed2002

Laser-based non-fluorescence detection techniques for liquid separation systems.

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.

Lasers↗

PubMed2002

Evaluation of a high-resolution time-of-flight mass spectrometer for the gas chromatographic determination of selected environmental contaminants.

A benchtop high-resolution time-of-flight mass spectrometer (TOF MS) was evaluated for the determination of key organic microcontaminants. The major advantage of the TOF MS proved to be the high mass resolution of about 0.002 Da (10 ppm). Consequently, the detectability of polar pesticides, polynuclear aromatic hydrocarbons and polychlorinated biphenyls is excellent, and detection limits are in the order of 1-4 pg injected mass. Best mass spectral resolution was obtained for medium-scale peaks. It is a disadvantage that the calibration range is rather limited, viz. to about two orders of magnitude. The high mass spectral resolution was especially useful to improve the selectivity and sensitivity when analyzing target compounds in complex samples and to prevent false-positive identifications.

Calibration↗

PubMed2002

Trace-level determination of pesticides in water by means of liquid and gas chromatography.

The trace-level determination of pesticides and their transformation products (TPs) in water by means of liquid and gas chromatography (LC and GC) is reviewed. Special attention is given to the use of (tandem) mass spectrometry for identification and confirmation purposes. The complementarity of LC- and GC-based techniques and the potential of comprehensive GCXGC are discussed, and also the impressive performance of time-of-flight mass spectrometry. It is also indicated that, in the near future, the TPs rather than the parent compounds should receive most attention--with a better understanding of matrix effects and eluent composition on the ionization efficiency of analytes being urgently required. Finally, the merits of using much shorter LC columns, or even no column at all (flow-injection analysis) in target analysis are shown, and a more cost-efficient and sophisticated strategy for monitoring programmes is briefly introduced.

Chromatography, Gas↗

PubMed2002

Liquid chromatographic-tandem mass spectrometric determination of selected sulphonamides in milk.

Liquid chromatography-tandem mass spectrometry is used for the quantitative analysis of selected sulphonamides in milk. Ultrafiltration is the only sample pre-treatment technique which is required. Consequently, sample throughput is much higher than with conventional procedures, and analyte recoveries are high. As for quantification, both external standard and isotope dilution calibration yield satisfactory results. The method is fully validated for five sulphonamides with a maximum residue limit of 100 microg/kg, and which are included in the Dutch control programme on residues. Furthermore, results are presented on the applicability of the method to detect compounds at a much lower concentration level exemplified by a banned sulphonamide, dapsone, which has a provisional action limit of 5 microg/kg. The main conclusion is that the present, novel approach to the trace-level determination of veterinary drugs is simple and straightforward and has a wide-ranging application potential which is briefly exemplified by the analysis of selected benzimidazoles in milk by essentially the same procedure.

Animals↗

PubMed2002

High-resolution separation of polychlorinated biphenyls by comprehensive two-dimensional gas chromatography.

Comprehensive two-dimensional gas chromatography (GC x GC) with micro electron-capture detection (microECD) has been optimised for the separation of polychlorinated biphenyl congeners with emphasis on the separation of 12 toxic non- and mono-ortho chlorinated biphenyls (CBs), viz. CBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169 and 189. The selection of the first- and second-dimension columns and the temperature programme optimisation were carried out with a mixture of 90 CBs and the results are compared with those of one-dimensional GC. A complete separation of all 12 priority CBs was obtained with two column combinations, HP-1-HT-8 and HP-1-SupelcoWax-10. With the HP-1-HT-8 column set, ordered structures show up in the two-dimensional plane, with the number of chlorine substituents and their position (ortho vs. non-ortho) being the main parameters of interest. This can help with congener identification. Estimated detection limits are excellent, i.e. about 10 fg. To illustrate the potential and the versatility of GC x GC-microECD, a cod liver extract and a standard mixture of the 17 most toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans together with 90 CBs were analysed as an application.

Chromatography, Gas↗

PubMed2002

Net fluxes of pesticides from the Scheldt Estuary into the North Sea: a model approach.

A hydrological model was constructed with the commercially available modelling environment ECoS for the calculation of mixing plots of dissolved pesticide concentrations in the Scheldt Estuary. The model was based on a one-dimensional advection-dispersion equation and dispersion coefficients were calculated from measured salinity profiles. The model could correctly predict the movement of water masses within the estuary. Nominal flushing times of the estuary were calculated with the fraction-of-freshwater method and ranged between 25 and 95 days, depending on the freshwater discharge. Model calculations demonstrated that the application-related time profiles of pesticide input may well induce curvature in the calculated estuarine mixing plot even if the pesticide behaves conservatively. Calculated mixing plots were compared with experimental data and good agreement was obtained between the measurements and the conservative mixing plot of atrazine. For metolachlor an additional direct emission had to be modelled to explain the differences between the experimental data and the conservative mixing plot. For dichlorvos and simazine. on the other hand, an estuarine loss constant had to be included in the model. Using a least-squares procedure the estuarine loss constants for dichlorvos and simazine were estimated at half-lives of five and 26 days, respectively. Because mixing plots were strongly influenced by the time profiles of pesticide input, standard procedures in which net fluxes are calculated from mixing plots, were not applicable. Therefore, net fluxes were calculated with a newly developed procedure in which the estuarine loss constants and the estuarine flushing time were combined. For the non-conservative compounds dichlorvos and simazine, the net fluxes to the North Sea were found to be 96 and 64%, respectively, lower than the gross fluxes transported by the River Scheldt.

Agriculture↗