Publications by authors named "Udo A Th Brinkman"

43 Publications

Peak clustering in two-dimensional gas chromatography with mass spectrometric detection based on theoretical calculation of two-dimensional peak shapes: the 2DAid approach.

J Chromatogr A 2011 Oct 3;1218(43):7878-85. Epub 2011 Sep 3.

Free University, Department of Analytical Chemistry, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

A method is presented to facilitate the non-target analysis of data obtained in temperature-programmed comprehensive two-dimensional (2D) gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-ToF-MS). One main difficulty of GC×GC data analysis is that each peak is usually modulated several times and therefore appears as a series of peaks (or peaklets) in the one-dimensionally recorded data. The proposed method, 2DAid, uses basic chromatographic laws to calculate the theoretical shape of a 2D peak (a cluster of peaklets originating from the same analyte) in order to define the area in which the peaklets of each individual compound can be expected to show up. Based on analyte-identity information obtained by means of mass spectral library searching, the individual peaklets are then combined into a single 2D peak. The method is applied, amongst others, to a complex mixture containing 362 analytes. It is demonstrated that the 2D peak shapes can be accurately predicted and that clustering and further processing can reduce the final peak list to a manageable size.
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http://dx.doi.org/10.1016/j.chroma.2011.08.081DOI Listing
October 2011

Characterization of olive oil volatiles by multi-step direct thermal desorption-comprehensive gas chromatography-time-of-flight mass spectrometry using a programmed temperature vaporizing injector.

J Chromatogr A 2008 Apr 29;1186(1-2):228-35. Epub 2007 May 29.

LECO Instrumente, Department of Separation Science, Marie-Bernays-Ring 31, 41199 Mönchengladbach, Germany.

The feasibility of a versatile system for multi-step direct thermal desorption (DTD) coupled to comprehensive gas chromatography (GC x GC) with time-of-flight mass spectrometric (TOF-MS) detection is studied. As an application the system is used for the characterization of fresh versus aged olive oil after treatment at 70, 175, 250 and 600 degrees C.
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http://dx.doi.org/10.1016/j.chroma.2007.05.066DOI Listing
April 2008

Analytical separation and detection methods for flavonoids.

J Chromatogr A 2006 Apr 14;1112(1-2):31-63. Epub 2006 Feb 14.

Quest International, Department of Analytical Research and Development, Huizerstraatweg 28, 1411 GP Naarden, The Netherlands.

Flavonoids receive considerable attention in the literature, specifically because of their biological and physiological importance. This review focuses on separation and detection methods for flavonoids and their application to plants, food, drinks and biological fluids. The topics that will be discussed are sample treatment, column liquid chromatography (LC), but also methods such as gas chromatography (GC), capillary electrophoresis (CE) and thin-layer chromatography (TLC), various detection methods and structural characterization. Because of the increasing interest in structure elucidation of flavonoids, special attention will be devoted to the use of tandem-mass spectrometric (MS/MS) techniques for the characterization of several important sub-classes, and to the potential of combined diode-array UV (DAD UV), tandem-MS and nuclear magnetic resonance (NMR) detection for unambiguous identification. Emphasis will be on recent developments and trends.
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http://dx.doi.org/10.1016/j.chroma.2006.01.019DOI Listing
April 2006

Changed isoflavone levels in red clover (Trifolium pratense L.) leaves with disturbed root nodulation in response to waterlogging.

J Chem Ecol 2005 Jun;31(6):1285-98

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.

The effect of disturbed root nodulation on the quantitative and qualitative composition of the main isoflavonoid glucoside malonates, glucosides, and aglycones in the leaves of Trifolium pratense L. grown under waterlogging conditions was investigated. Isoflavonoids are involved in the regulation of root nodule activity and the establishment of the mycorrhizal association. Isoflavonoid determination was performed using reversed-phase liquid chromatography coupled to mass spectrometric and UV absorbance detection. In response to waterlogging, the concentrations of biochanin A and biochanin A-7-O-glucoside malonate, biochanin A-7-O-glucoside, and genistein-7-O-glucoside in the leaves increased two- to threefold after a lag period of 3 wk because of disturbed root nodulation. The other isoflavones detected formononetin, formononetin-7-O-glucoside malonate, and formononetin-7-O-glucoside-did not show any significant changes related to waterlogging. After restoring normal soil water conditions, the concentrations of biochanin A and its glucoside and glucoside-malonate rapidly returned to the initial values, whereas the concentration of genistein-7-O-glucoside remained high.
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http://dx.doi.org/10.1007/s10886-005-5286-1DOI Listing
June 2005

Flow regime at ambient outlet pressure and its influence in comprehensive two-dimensional gas chromatography.

J Chromatogr A 2005 Sep;1086(1-2):141-50

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, De Boelelaan 1083, 1081 HVAmsterdam, The Netherlands.

With method development in one-dimensional GC already being a tedious task, developing GC x GC methods is even more laborious. The majority of the present GC x GC applications are derived from previously optimised 1D-GC methods, from which especially the carrier gas flow settings are copied. However, in view of the high pressure inside the first-dimension column (high flow resistance of the narrow-bore second-dimension column), diffusion in the first column is much slower than in 1D-GC. Proper optimisation of the column combination and the carrier gas flow can considerably improve separations in GC x GC. To assist in the process of selecting column dimensions and flow rate optimization, we have developed a computer programme, based on Excel, that enables quick and simple calculation for all types of column combinations. The programme merely needs column dimensions and carrier gas type as input parameters and calculates all resolution and velocity parameters of the GC x GC separation by using flow rate and plate height equations. From the calculations a number of interesting conclusions can be drawn. As an example, the calculations clearly show that the majority of column combinations reported up till now have been operated at a far from optimal flow -- and, consequently, a far from optimal resolution. Probably even more important is the conclusion that the majority of column combinations used so far, i.e. those with 100 microm I.D. second-dimension columns, are not necessarily the best choice for GC x GC.
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http://dx.doi.org/10.1016/j.chroma.2005.05.086DOI Listing
September 2005

Twin comprehensive two-dimensional gas chromatographic system: concept and applications.

J Chromatogr A 2005 Sep;1086(1-2):128-34

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HVAmsterdam, The Netherlands.

A twin GC x GC system has been designed which enables the analysis of a sample by means of two different and independent column combinations simultaneously. Both combinations are incorporated in the same oven, using the same temperature programme, and are fed using a 50:50 column-entrance-split. It is demonstrated that, employing combinations of a conventional non-polar x polar and a reversed-type polar x non-polar column set, the information content is as high, and the analytical performance is as good as when using two separate GC x GC systems. That is, there is an appreciable gain of time and a reduction of costs without any loss of quality. The general usefulness of performing, and comparing two mutually different GC x GC runs is further illustrated with FAMEs in olive oil, and pollutants in a sediment sample.
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http://dx.doi.org/10.1016/j.chroma.2004.12.021DOI Listing
September 2005

Improved determination of flavour compounds in butter by solid-phase (micro)extraction and comprehensive two-dimensional gas chromatography.

J Chromatogr A 2005 Sep;1086(1-2):99-106

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HVAmsterdam, The Netherlands.

The practicability and potential of comprehensive two-dimensional gas chromatography (GC x GC) coupled to both conventional flame ionisation (FID) and time-of-flight mass spectrometric (TOF-MS) detection, were compared with those of conventional one-dimensional (1D) GC, with the determination of flavour compounds in butter as an application. For polar flavour compounds, which were collected from the aqueous fraction of butter by means of solid-phase extraction (SPE), it was found that GC x GC dramatically improves the overall separation. Consequently, quantification and preliminary identification based on the use of ordered structures, can be performed more reliably. The improvement effected by replacing 1D-GC by GC x GC is considerable also in the case of TOF-MS detection, as illustrated by the high match factors generally obtained during identification. GC x GC was also used successfully for the characterisation of volatile flavour compounds in the headspace of butter collected by solid-phase microextraction (SPME) and to study the effect of heat treatment on the composition of butter samples in more detail.
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http://dx.doi.org/10.1016/j.chroma.2005.05.094DOI Listing
September 2005

Trace analysis of polychlorinated dibenzo-p-dioxins, dibenzofurans and WHO polychlorinated biphenyls in food using comprehensive two-dimensional gas chromatography with electron-capture detection.

J Chromatogr A 2005 Sep;1086(1-2):61-70

Environmental Chemistry, Department of Chemistry, Institute of Environmental Chemistry, Umeå University, SE-90187 Umeå, Sweden.

Trace analysis of 2,3,7,8-polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and the 12 WHO-PCBs (four non-ortho and eight mono-ortho congeners that have been assigned toxic equivalence factors, TEFs, by the World Health Organisation) was conducted by comprehensive two-dimensional gas chromatography with a micro electron-capture detector (GC x GC-microECD). Four food matrices (fish oil from herring, spiked cows' milk, vegetable oil and an eel extract) were analysed by two GC x GC laboratories, and four GC-HRMS laboratories generated reference values. The two GC x GC laboratories used different column combinations for separating the target analytes. For the first dimension, non-polar DB-XLB and VF-1 columns were used, and for the second dimension, an LC-50 liquid crystalline column with unique selectivity for planar compounds. The congener-specific and total toxic equivalence (TEQ) data obtained using DB-XLB x LC-50 were in good agreement with results obtained by the GC-HRMS laboratories. The WHO-PCB data obtained with the VF-1 x LC-50 combination was also good, but the PCDD/F concentrations were sometimes overestimated due to matrix interferences. GC x GC-microECD using DB-XLB x LC-50 seems to fulfil the European Community requirements of a screening method for PCDD/F and WHO-PCB TEQ in food.
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http://dx.doi.org/10.1016/j.chroma.2004.11.071DOI Listing
September 2005

Characterization of lipids in complex samples using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry.

J Chromatogr A 2005 Sep;1086(1-2):2-11

Department of Environmental Chemistry IIQAB-CS, C, c/Jordi Girona No. 18-26, 08034 Barcelona, Spain.

Most lipids are a complex mixture of classes of compounds such as fatty acids, fatty alcohols, diols, sterols and hydroxy acids. In this study, the suitability of comprehensive two-dimensional gas chromatography coupled to a time-of-light mass spectrometer is studied for lipid characterization in complex samples. With lanolin, a refined wool wax, as test sample, it is demonstrated that combined methylation plus silylation is the preferred derivatization procedure to achieve (i) high-quality GC x GC separation and (ii) easily recognizable ordered structures in lipid analysis. Optimization of the GC x GC column combination, the influence of the temperature programme on the quality of the separation, and the potential and limitations of automated TOF-MS-based identification are discussed. The combined power of a 2D separation, ordered structures and MS detection is illustrated by the identification of several minor sample constituents.
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http://dx.doi.org/10.1016/j.chroma.2005.05.093DOI Listing
September 2005

Fast miniaturised sample preparation for the screening and comprehensive two-dimensional gas chromatographic determination of polychlorinated biphenyls in sludge.

J Sep Sci 2005 Jul;28(11):1121-8

Vrije Universiteit, Department of Analytical Chemistry and Applied Spectroscopy, de Boelelaan 1083,1081 HV Amsterdam, The Netherlands.

Polychlorinated biphenyls (PCBs) in sludge are usually extracted by a technique such as Soxhlet with subsequent fractionation prior to long GC runs using GC-ECD or GC-HRMS. In this study, the extraction of selected chlorinated biphenyls (CBs) from a spiked sludge sample by three rapid techniques, i.e. ultrasonic (USE), pressurised-liquid (PLE), and microwave-assisted (MAE) extraction using a domestic microwave, was studied, with subsequent direct GC-ECD, GC-MS, or GC x GC-microECD analysis of the extracts. The main goal was to select an appropriate, and miniaturised, extraction method after only a brief optimisation and demonstrate the power of GC x GC analysis of dirty extracts. For PLE similar CB recoveries were found when extracting with either n-hexane or n-hexane/acetone (1/1). For USE and MAE, n-hexane/acetone (1/1) was the preferred extraction solvent. USE gave the best recoveries (80-95%; except 130% for CB 105). The only clean-up needed prior to GC-MS or GC x GC-gECD analysis was the removal of sulphur-containing compounds. GC-ECD was not suitable for these dirty extracts. The lowest LODs for the CBs (20 fg or 0.1 ng/g sludge) were found when combining USE and GC x GC-microECD, because of the powerful extraction, high separation power and excellent detectability provided by this technique.
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http://dx.doi.org/10.1002/jssc.200301733DOI Listing
July 2005

Polychlorinated biphenyls in marine sediments from the southern North Sea and Scheldt estuary: a ten-year study of concentrations, patterns and trends.

J Environ Monit 2005 Jul 9;7(7):701-9. Epub 2005 Jun 9.

Management Unit Mathematical Models of the North Sea, Royal Belgian Institute for Natural Sciences, 3e and 23e Linieregimentsplein, B-8400 Oostende, Belgium.

The paper reports the concentrations and patterns of CBs in sediments of the Belgian part of the southern North Sea and the Scheldt estuary for the period 1991-2001. The long-term analytical performance was well within the quality assurance boundaries set at the outset of the study and is consistent with the state of the art for this type of analysis. The CB concentrations (given as the median of the sum of IUPAC Nos 28, 52, 101, 118, 138, 153 and 180) vary between 0.1 microg kg(-1) and 50 microg kg(-1) dry weight in the total sediment and it could be demonstrated that CB patterns in the fine fraction of the sediment were closely similar throughout the investigated area. Isolation of the fine fraction (<63 microm) by sieving can be regarded as a physical normalisation to reduce the differences in sediment granulometric composition. It allows for a better understanding of CB distribution and patterns and improves the trend analysis. A significant downward trend could not be found at any of the stations, which suggests that CB levels have not been changing in the area of interest in the past decade.
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http://dx.doi.org/10.1039/b419240kDOI Listing
July 2005

Comprehensive two-dimensional gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer: principles and applications.

J Chromatogr A 2005 Mar;1067(1-2):245-54

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

The principles, practicability and potential of comprehensive two-dimensional (2D) gas chromatography coupled to a rapid-scanning quadrupole mass spectrometer (GC x GC-qMS) for the analysis of complex flavour mixtures in food, allergens in fragrances and polychlorinated biphenyls (PCBs) were studied. With a scan speed of 10,000 amu/s, monitoring over a mass range of up to 200 atomic mass unit (amu) can be achieved at an acquisition frequency of 33 Hz. Extending this mass range and/or increasing the data acquisition frequency results in a loss of spectral quality. Optimal parameter settings allow, next to unambiguous identification/confirmation of target compounds on the basis of high-quality mass spectra, fully satisfactory quantification (three to four modulations per peak) with linear calibration plots and detection limits in the low-pg level. The potential of time-scheduled data acquisition to increase the effective mass range within one GC x GC run was also explored. The analyses, with baseline separation of the flavours, allergens and PCB target compounds, took less than 30 min.
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http://dx.doi.org/10.1016/j.chroma.2004.09.094DOI Listing
March 2005

Characterization of monofluorinated polycyclic aromatic compounds by 1H, 13C and 19F NMR spectroscopy.

Magn Reson Chem 2005 Jul;43(7):588-94

Department of Chemistry, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.

Monofluorinated polycyclic aromatic hydrocarbons (F-PAHs) have attracted much attention in analytical, environmental, toxicological and mechanistic studies because of their physico-chemical properties, which are closely similar to those of the parent PAHs. Because of this, full NMR characterization has become of interest. Complete 1H, 13C and 19F NMR chemical shifts, and also 1J(H,C), (n)J(C,F), (n)J(H,F) and (n)J(H,H) coupling constants, have been assigned for the F-PAHs 1-fluoronaphthalene, 2-fluorofluorene, 5-fluoroacenaphthylene, 2-fluorophenanthrene, 3-fluorophenanthrene, 3-fluorofluoranthene, 1-fluoropyrene, 1-fluorochrysene, 2-fluorochrysene, 3-fluorochrysene and 9-fluorobenzo[k]fluoranthene. To allow comparison with the corresponding parent PAHs, the 1H and 13C chemical shifts of acenaphthylene, phenanthrene, fluoranthene, pyrene and benzo[k]fluoranthene were determined. Chemical shift increments and the effects on the coupling constants from the fluorine substitution are discussed.
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http://dx.doi.org/10.1002/mrc.1584DOI Listing
July 2005

Retention-time database of 126 polybrominated diphenyl ether congeners and two bromkal technical mixtures on seven capillary gas chromatographic columns.

J Chromatogr A 2005 Feb;1065(2):239-49

Netherlands Institute for Fisheries Research, Animal Sciences Group, Wageningen UR, 1970 IJmuiden, The Netherlands.

The elution order of 126 polybrominated diphenyl ethers (PBDE) was determined for seven different gas chromatographic (GC) stationary phases. The resulting database facilitates selection of the most suitable GC columns for developing a quantitative, congener-specific BDE analysis and the testing of retention prediction algorithms based on structure relationships of GC phases and congener substitution patterns. In addition, co-elutions of the principal BDE congeners with other BDEs and/or with other brominated flame retardants were investigated and, as an application, the composition of two Bromkal mixtures (70-5DE and 79-8DE) was studied.
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http://dx.doi.org/10.1016/j.chroma.2004.12.059DOI Listing
February 2005

Comprehensive two-dimensional gas chromatography--a powerful and versatile technique.

Analyst 2005 Feb;130(2):123-7

Free University, Department of Analytical Chemistry, Amsterdam, The Netherlands.

Comprehensive two-dimensional gas chromatography (GC x GC) was introduced about a decade ago and is, today, rapidly become a powerful and widely applicable technique for the characterisation and analysis of a variety of complex samples. GC x GC provides structurally ordered chromatograms in the 2D plane, and features an impressive peak capacity. Combining GC x GC and time-of-flight mass spectrometry (ToFMS), with its fast acquisition rates and excellent deconvolution potential, has been an important step forward which enables identification and identity confirmation of large numbers of target analytes and unknowns in one run. Up until now, some 150 papers have been published, fish and food, environmental and air analysis. Polyhalogenated aromatics and other priority pollutants, flavours and fragrances, fatty acid methyl esters and essential oils, are among the classes of compounds which frequently receive attention. In summary, GC x GC is increasingly being recognised as the separation technique of choice in problem areas.
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http://dx.doi.org/10.1039/b407372jDOI Listing
February 2005

Miniaturised pressurised liquid extraction of chloroanilines from soil with subsequent analysis by large-volume injection-gas chromatography-mass spectrometry.

J Chromatogr A 2004 Nov;1058(1-2):243-9

Department of Analytical Chemistry and Applied Spectroscopy, Free University, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

A number of chloroanilines were extracted from soil by means of miniaturised pressurised liquid extraction (PLE). The extraction procedure was optimised for both large-volume on-column (LV-OC) and programmed-temperature vaporisation (PTV) injections combined with GC-MS. Hexane was the only extraction solvent suited for LV-OC and hexane/acetone gave the best results when using a PTV. Overall, the hexane/acetone-plus-PTV procedure shows better results than the hexane-plus-LV-OC method in terms of analyte recovery (36-109% versus 5-87%), repeatability (8-13% versus 4-31%) and detection limits. Both approaches allow detection of the chloroanilines in complex soil samples down to the 5-50 ng/g range. However, the PTV-based procedure is superior as regards robustness: over one hundred samples can be analysed without any maintenance being required.
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http://dx.doi.org/10.1016/j.chroma.2004.05.044DOI Listing
November 2004

Group-type characterisation of mineral oil samples by two-dimensional comprehensive normal-phase liquid chromatography-gas chromatography with time-of-flight mass spectrometric detection.

J Chromatogr A 2004 Nov;1058(1-2):217-21

LECO Instrumente, Separation Science Group, Marie-Bernays-Ring 31, 41199 Mönchengladbach, Germany.

Normal-phase liquid chromatography (NPLC) and capillary gas chromatography (GC) are complementary techniques, which makes them ideally suited for hyphenated and comprehensive coupling. In this work, an LC and a GC equipped with a time-of-flight mass spectrometer were on-line and comprehensively coupled (LC x GC-ToF MS) for the analysis of mineral oil samples. Classes of compounds present in the oil like paraffins, mono-aromatic and multi-aromatic compounds were separated by normal-phase LC. with a subsequent boiling-point separation within each class by means of GC. Sub-groups present in each class of compounds were distinguished by selecting their unique masses.
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http://dx.doi.org/10.1016/j.chroma.2004.08.083DOI Listing
November 2004

Comprehensive two-dimensional gas chromatography of complex samples by using a 'reversed-type' column combination: application to food analysis.

J Chromatogr A 2004 Oct;1054(1-2):47-55

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

The practicability and potential of a non-orthogonal approach in comprehensive two-dimensional gas chromatography (GC x GC) were studied and compared to those of the orthogonal approach for two different complex matrices, and using conventional flame ionisation (FID) and time-of-flight mass spectrometry (ToF MS) detection. The separation of a diesel oil showed that the non-orthogonal approach also provides interesting, but completely reversed, ordered structures. For the more extensively studied flavour analysis in food samples, improved peak shapes and, also, different types of ordered structures and retention behaviour, and improved detectability for polar compounds make the two approaches complementary to each other. As a consequence, identification and/or determination of targets and/or unknowns can be performed more reliably. Analytical performance (close to three-order linearity; LODs, 2-30 pg injected in most cases; R.S.D.s, 1-6% (n = 6)) was fully satisfactory.
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October 2004

Liquid chromatography coupled to nuclear magnetic resonance spectroscopy for the identification of isoflavone glucoside malonates in T. pratense L. leaves.

J Sep Sci 2004 Sep;27(13):1061-70

Vrije Universiteit, Department of Analytical Chemistry and Applied Spectroscopy, de Boelelaan 1083, 1081 HV Amsterdam, the Netherlands.

Previous studies revealed that the main isoflavones in extracts of leaves of T. pratense L. are biochanin A and formononetin, their 7-O-glucosides, and two glucoside malonate isomers of each of them. Since LC-MS(/MS) did not provide sufficient information to distinguish the glucoside malonate isomers, in the present paper LC-NMR as well as off-line two-dimensional NMR were used to obtain further structural information. Matrix solid-phase dispersion (MSPD) was applied to obtain sufficiently high analyte concentrations to perform LC-NMR. Stop-flow reversed-phase LC-NMR was performed using a gradient of deuterated water and deuterated acetonitrile. Offline COSY and NOESY experiments were carried out to determine the positions of the glucose moiety on the flavonoid aglycone, and of the malonate moiety on the glucose. Based on the fragmentation patterns in MS/MS and the NMR spectra, the two formononetin glucoside malonate isomers were identified as 7-O-beta-D-glucoside 6"-O-malonate and 7-O-beta-D-glucoside 4"-O-malonate; i.e. they only differ in the substitution position of the malonate group on the glucoside ring. The biochanin A glucoside malonate isomers, however, have quite different structures. The main and later eluting isomer is biochanin A 7-O-beta-D-glucoside 6"-O-malonate, and the minor and earlier eluting isomer is 5-hydroxy-7-methoxyisoflavone 4'-O-beta-D-glucoside 4"-O-malonate: the positions of the methoxy group and the glucoside 6"-O-malonate group on the flavonoid skeleton are interchanged.
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http://dx.doi.org/10.1002/jssc.200401844DOI Listing
September 2004

Automated on-line comprehensive two-dimensional LC x GC and LC x GC-ToF MS: instrument design and application to edible oil and fat analysis.

J Sep Sci 2004 Apr;27(5-6):397-409

LECO Instrumente, Separation Science Group, Marie-Bernays-Ring 31, 41199 Mönchengladbach, Germany.

After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LC x GC) has been studied. Important aspects to consider when developing automated LG x GC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LC x GC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LC x GC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.
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http://dx.doi.org/10.1002/jssc.200301676DOI Listing
April 2004

On-line LC-GC and comprehensive two-dimensional LCxGC-ToF MS for the analysis of complex samples.

Anal Bioanal Chem 2004 Apr 22;378(8):1944-7. Epub 2004 Jan 22.

Central Analytical Science, Unilever Research and Development, P.O. Box 114, 3130 AC, Vlaardingen, The Netherlands.

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http://dx.doi.org/10.1007/s00216-003-2484-yDOI Listing
April 2004

Comprehensive two-dimensional gas chromatography-a powerful and widely applicable technique.

Anal Bioanal Chem 2004 Apr 28;378(8):1939-43. Epub 2004 Jan 28.

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit Amsterdam, de Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.

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http://dx.doi.org/10.1007/s00216-003-2478-9DOI Listing
April 2004

Liquid chromatography with triple-quadrupole and quadrupole-time-of-flight mass spectrometry for the determination of micro-constituents - a comparison.

Anal Bioanal Chem 2004 Apr 5;378(7):1754-61. Epub 2004 Feb 5.

Laboratory for Organic-analytical Chemistry, National Institute for Public Health and the Environment (RIVM), PO Box 1, 3720 BA, Bilthoven, The Netherlands.

The potential of liquid chromatography with triple-quadrupole mass spectrometry (LC-QqQ MS) was compared to that of quadrupole time-of-flight mass spectrometry (LC-Q-ToF MS) for the determination of microconstituents. Three applications were studied: (1) the ng/l quantification of five human drugs in surface water and waste-water effluents; (2) the quantification and confirmation of three corticosteroids in bovine urine at concentrations of 1-100 microg/l, and; (3) the confirmation of nicotine in rat plasma. In all cases, the criteria of the EU Commission Decision 2002/657/EC were followed (for confirmation analysis two MS/MS ions were monitored, and the ratio of their abundances were calculated and compared with those of standards). With both techniques fully satisfactory results were obtained in almost all instances. That is, unequivocal confirmation according to the most stringent EU criteria, those for "illegal compounds", was possible.One main advantage of LC-Q-ToF MS is that for identification and confirmation purposes, full MS/MS spectra are available after a single injection: no second injection, as required with QqQ MS, is needed. As well as the increased efficiency, the enhanced selectivity due to the impressive mass selectivity of LC-Q-ToF MS must be emphasized, which allows accurate masses of fragment ions to be calculated. Method characteristics such as linear dynamic range and repeatability were found to be essentially the same for both techniques, but LC-QqQ MS has the advantage that its detection limits are somewhat lower.
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http://dx.doi.org/10.1007/s00216-003-2485-xDOI Listing
April 2004

AT-column, a novel concentrating technique for large-volume injections in gas chromatography.

J Chromatogr A 2004 Jan;1023(2):165-74

ATAS GL International, P.O. Box 17, 5500AA Veldhoven, The Netherlands.

Nowadays, large-volume injection is widely used for the GC determination of trace analytes, specifically to improve detectability. The most popular injectors for large-volume injections are the programmable temperature vaporisation (PTV) injector and the cold on-column (COC) injector, where each device has its own advantages and limitations. The novel AT-column concentrating technique combines features of two other injection techniques, loop-type large-volume and vapour overflow. AT-column injection is based on solvent evaporation in an empty liner with solvent vapour discharge via the split line. Little or no optimisation is required. The only relevant parameter is the injection temperature which can easily be calculated using the equation of Antoine. As an application, AT-column injection is combined with GC-MS for the trace-level determination of labile analytes and with GC-flame ionisation detection for the analysis of high molecular weight polymer additives. In summary, AT-column is an injection technique that combines the inertness of the COC, and the flexibility and robustness of the PTV large-volume technique.
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http://dx.doi.org/10.1016/j.chroma.2003.10.031DOI Listing
January 2004

Determination of VOCs in yellow eel from various inland water bodies in Flanders (Belgium).

J Environ Monit 2003 Dec;5(6):876-84

Management Unit Mathematical Models of the North Sea, Royal Belgian Institute for Natural Sciences, 3e and 23e Linieregimentsplein, B-8400 Oostende, Belgium.

Twenty freshwater eels caught in Flanders (Belgium) were analysed by GC-MS for a total of 52 VOCs. The most prominent VOCs are the BTEX and a number of chlorinated compounds such as chloroform and tetrachloroethene. The observed concentrations which, typically, were in the low ng/g wet weight range, could be linked to the major emission sources and the present study gives new evidence that combustion of fossil fuels is a major source of BTEX in the environment. The concentration levels in eels seem to be a reflection of the actual concentrations in their environment. For eels from the same location similar patterns and concentrations were observed, and the concentrations agree with what can be expected from those of the water column. Generally speaking, the observed concentrations do not seem to pose a threat for organisms. More definite statements will, however, require a larger dataset. The study suggests that the yellow eel can possibly be used as a biomonitor or sentinel organism for VOCs.
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http://dx.doi.org/10.1039/b307862kDOI Listing
December 2003

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection for the trace analysis of flavour compounds in food.

J Chromatogr A 2003 Nov;1019(1-2):157-72

Vrije Universiteit, Department of Analytical Chemistry and Applied Spectroscopy, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

The practicability and potential of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOF-MS) for the analysis of complex flavour mixtures in food were studied. With the determination of key flavour targets in dairy samples as an example, it was demonstrated that GC x GC dramatically improves the separation. As a consequence, identification and, more importantly, quantification down to the ng/g level can be performed more reliably: background interferences largely disappear. Next to the peak table generated from the GC-TOF-MS software after data processing, the additional use of well-ordered patterns in the 2D-plane and information from second-dimension retention times can substantially help the identification of unknowns. The technique was successfully used for an evaluation of extraction techniques and the characterisation of different types of samples.
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http://dx.doi.org/10.1016/s0021-9673(03)01131-2DOI Listing
November 2003

Comprehensive two-dimensional gas chromatography with atomic emission detection and correlation with mass spectrometric detection: principles and application in petrochemical analysis.

J Chromatogr A 2003 Nov;1019(1-2):89-99

Department of Analytical Chemistry and Applied Spectroscopy, Vrije Universiteit, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

Comprehensive gas chromatography (GC x GC) has been combined with atomic emission detection (AED) to enable element-selective detection. Under optimised experimental conditions, the requirement of minimum five data points across a peak can be obtained even for analytes eluting early from the second-dimension column. Simple manipulation of the results allows the combined presentation of up to four sets of elemental data in one two-dimensional plot. GC x GC with AED and mass spectrometric (MS) detection in petrochemical analysis for fingerprinting as well as the identification of N- and S-containing unknowns is presented as an application.
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http://dx.doi.org/10.1016/s0021-9673(03)01301-3DOI Listing
November 2003

Evaluation of modulators and electron-capture detectors for comprehensive two-dimensional GC of halogenated organic compounds.

J Chromatogr A 2003 Nov;1019(1-2):65-77

Department of Analytical Chemistry and Applied Spectroscopy, Faculty of Sciences, Vrije Universiteit, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

Different cryogenic and a heated GC x GC modulator(s) were evaluated and compared for the analysis of high-boiling halogenated compounds. The cryogenic modulators investigated were: (i) the longitudinally modulated cryogenic system; (ii) the liquid-nitrogen-cooled jet modulator (KT2001); (iii) a dual-jet CO2 modulator (made in-house); (iv) a semi-rotating cryogenic modulator (made in-house) and (v) a CO2 loop modulator (KT2003); the heated modulator was the slotted heater system (sweeper). Each modulator was optimised with respect to analyte peak widths at half height in the second-dimension. n-Alkanes, chlorinated alkanes, polychlorinated biphenyls (PCBs) and fluorinated polycyclic aromatic hydrocarbons (F-PAHs) were used as test analytes. The flow rate of the coolant was found to be an important parameter, i.e. the flow rate of the gaseous nitrogen in the KT2001, and of the liquid CO2 in the other cryogenic modulators. For the slotted heater the stroke velocity and pause time were important parameters. This modulator had a limited application range in terms of temperature due to a necessary 100 degrees C difference between sweeper and oven temperature. All cryogenic modulators were found to be suitable for the GC x GC analysis of high-boiling compounds, but the CO2 modulators are to be preferred to the KT2001 due to a wider application range and slightly narrower peaks. As regards the performance of three commercially available electron-capture detectors (ECDs), the aim was to obtain narrow peak widths in GC x GC, i.e. to avoid band broadening caused by the cell volume. The most important parameters were the flow rate of the make-up gas and the detector temperature which both should be as high as possible. Comparison of analyte peak widths obtained with ECD mode and flame ionisation detection (FID) showed that all ECDs exhibited band broadening compared to the FID. The narrowest peaks were obtained with the Agilent micro-ECD, which has a cell volume of only 150 microl.
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http://dx.doi.org/10.1016/s0021-9673(03)01237-8DOI Listing
November 2003

Capillary electrophoresis coupled on-line with ultraviolet resonance Raman spectroscopy.

Anal Chem 2003 Nov;75(21):5697-702

Department of Analytical Chemistry and Applied Spectroscopy, Laser Centre, Vrije Universiteit Amsterdam, de Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.

Capillary electrophoresis (CE) and resonance Raman spectroscopy (RRS) with excitation in the deep ultraviolet (UV) region (lambda(ex): 244 or 257 nm) were coupled on-line. The potential of this hyphenated technique, denoted as CE-UV-RRS, for analyte confirmation/identification purposes was explored with aromatic sulfonic acids and nucleotides as test compounds. Good-quality UV-RRS spectra could be recorded on-the-fly. Identification limits for the nucleotides were in the 10-125 microg/mL range. The RRS spectra showed sufficient characteristic features to enable analyte confirmation. In addition, the identification power of UV-RRS was studied with substituted pyrenes as model compounds. The compounds were distinguishable on the basis of their RRS spectra at 244 nm.
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http://dx.doi.org/10.1021/ac034555zDOI Listing
November 2003

Liquid chromatography with triple-quadrupole or quadrupole-time of flight mass spectrometry for screening and confirmation of residues of pharmaceuticals in water.

Anal Bioanal Chem 2004 Feb 16;378(4):955-63. Epub 2003 Oct 16.

Laboratory for Analytical Chemistry, National Institute for Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands.

LC-MS-MS has been performed with triple-quadrupole (QqQ) and quadrupole-time of flight (Q-ToF) instruments and has been used for screening and confirmation of pharmaceuticals in surface, drinking, and ground water. Screening was based on monitoring of one specific MS-MS ion of the target compounds. Confirmation of the identity of the pharmaceuticals was based either on the monitoring of two specific MS-MS ions and calculation of the ratio of their intensities, or on the exact masses of MS-MS product ions obtained for a molecular ion by use of LC-Q-ToF MS. The set of pharmaceuticals included four analgesics (acetylsalicylic acid, diclofenac, ibuprofen, and paracetamol), three antibiotics (sulfamethoxazole, erythromycin, and chloramphenicol), five blood-lipid regulators and beta-blockers (fenofibrate, bezafibrate, clofibric acid, bisoprolol, and metoprolol), and the anti-epileptic drug carbamazepine. Limits of quantification ranged from 5 to 25 ng L(-1). Fifty-six samples were analysed and residues of the pharmaceuticals were detected in almost all surface and groundwater and in some drinking water samples. The identity of the compounds could be confirmed by use of both QqQ- and Q-ToF-based LC-MS-MS. However, the latter technique has the distinct advantage that a large number of pharmaceuticals can be screened and confirmed at low concentrations (1-100 ng L(-1)) in one run.
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http://dx.doi.org/10.1007/s00216-003-2253-yDOI Listing
February 2004
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