TY - JOUR AB - Comprehensive two-dimensional gas chromatography (GC × GC) is amongst the most powerful separation technologies currently existing. Since its advent in early 1990, it has become an established method which is readily available. However, one of its most challenging aspects, especially in hyphenation with mass spectrometry is the high amount of chemical information it provides for each measurement. The GC × GC community agrees that there, the highest demand for action is found. In response, the number of software packages allowing for in-depth data processing of GC × GC data has risen over the last couple of years. These packages provide sophisticated tools and algorithms allowing for more streamlined data evaluation. However, these tools/algorithms and their respective specific functionalities differ drastically within the available software packages and might result in various levels of findings if not appropriately implemented by the end users. This study focuses on two main objectives. First, to propose a data analysis framework and second to propose an open-source dataset for benchmarking software options and their specificities. Thus, allowing for an unanimous and comprehensive evaluation of GC × GC software. Thereby, the benchmark data includes a set of standard compound measurements and a set of chocolate aroma profiles. On this foundation, eight readily available GC × GC software packages were anonymously investigated for fundamental and advanced functionalities such as retention and detection device derived parameters, revealing differences in the determination of e.g. retention times and mass spectra. AU - Weggler, B.A.* AU - Dubois, L.M.* AU - Gawlitta, N. AU - Gröger, T.M. AU - Moncur, J.* AU - Mondello, L.* AU - Reichenbach, S.* AU - Tranchida, P.* AU - Zhao, Z.* AU - Zimmermann, R. AU - Zoccali, M.* AU - Focant, J.F.* C1 - 60715 C2 - 49576 CY - Radarweg 29, 1043 Nx Amsterdam, Netherlands TI - A unique data analysis framework and open source benchmark data set for the analysis of comprehensive two-dimensional gas chromatography software. JO - J. Chromatogr. A VL - 1635 PB - Elsevier PY - 2021 SN - 0021-9673 ER - TY - JOUR AB - The transplacental passage of thyroid hormones (THs) is of great significance since the maternal THs are vitally important in ensuring the normal fetal development. In this paper, we determined the concentrations of seven THs, viz. L-thyroxine (T4), 3,3',5-triiodo-l-thyronine (T3), 3,3',5'-triiodo-l-thyronine (rT3), 3,3'-diiodo-l-thyronine (T2), 3,5-diiodo-l-thyronine (rT2), 3-iodo-l-thyronine (T1) and 3-iodothyronamine (T1AM), in placenta using isotope dilution liquid chromatography quadrupole time-of-flight mass spectrometry. We optimized the method using isotopically labeled quantification standards (13C6-T4, 13C6-T3, 13C6-rT3 and 13C6-T2) and recovery standard (13C12-T4) in combination with solid-liquid extraction, liquid-liquid extraction and solid phase extraction. The linearity was obtained in the range of 0.5-150 pg uL-1 with R2 values >0.99. The method detection limits (MDLs) ranged from 0.01 ng g-1 to 0.2 ng g-1, while the method quantification limits (MQLs) were between 0.04 ng g-1 and 0.7 ng g-1. The spike-recoveries for THs (except for T1 and T1AM) were in the range of 81.0%-112%, with a coefficient of variation (CV) of 0.5-6.2%. The intra-day CVs and inter-day CVs were 0.5%-10.3% and 1.19%-8.88%, respectively. Concentrations of the THs were 22.9-35.0 ng g-1 T4, 0.32-0.46 ng g-1 T3, 2.86-3.69 ng g-1 rT3, 0.16-0.26 ng g-1 T2, and < MDL for other THs in five human placentas, and 2.05-3.51 ng g-1 T4, 0.37-0.62 ng g-1 T3, 0.96-1.3 ng g-1 rT3, 0.07-0.13 ng g-1 T2 and < MDL for other THs in five mouse placentas. The presence of T2 was tracked in placenta for the first time. This method with improved selectivity and sensitivity allows comprehensive evaluation of TH homeostasis in research of metabolism and effects of environmental contaminant exposures. AU - Li, Z.M. AU - Giesert, F. AU - Vogt Weisenhorn, D.M. AU - Main, K.M.* AU - Skakkebæk, N.E.* AU - Kiviranta, H.* AU - Toppari, J.* AU - Feldt-Rasmussen, U.* AU - Shen, H.* AU - Schramm, K.-W. AU - de Angelis, M. C1 - 52692 C2 - 44206 SP - 85-92 TI - Determination of thyroid hormones in placenta using isotope-dilution liquid chromatography quadrupole time-of-flight mass spectrometry. JO - J. Chromatogr. A VL - 1534 PY - 2018 SN - 0021-9673 ER - TY - JOUR AB - Research in the area of new nanomaterials has been given high priority as having an enormous economic potential. Due to marked antimicrobial effect, silver nanoparticles (AgNPs) are one of the most commercialized and successfully exploited nanomaterials in a wide range of medical and consumer products.In biological and environmental compartments, AgNPs undergo different transformations including interaction with organic molecules, such as proteins, and dissolution. Hyphenated systems consisting of capillary electrophoresis (CE) coupled to sensitive element detection like ICP-MS can be considered as the promising methods for speciation analysis of AgNPs. Here, we investigated applicability of different CE methods hyphenated to ICP-MS for speciation of AgNPs in biological systems.The paper presents approach to analyze species formed in interaction of AgNPs with metallothionein (MT) as model protein. As AgNPs might be coated by MTs in bio-fiuids, we installed first a CE-speciation method for MT-1 and MT-2. Although this separation was successful, no reproducible and well separated peaks for AgNPs or Ag* were achieved. Therefore, we focused on developing methods for separating MT-1, MT-2, Ag* and AgNPs. Several buffer conditions were tested to improve their separation and to minimize Ag-sticking to capillary walls. All compounds of interest in this paper, i.e. MT-1, MT-2, Ag+ and AgNPs, were well separated from each other using tetramethyl-ammoniumhydroxide as electrolyte. In mixed samples, we observed Ag+ being completely associated with MT-1, while Ag*-association with MT-2 was less: The highest quantity of Ag* was associated with a compound having low Cd-concentration, while another relevant fraction was bound to MT-2. Free Ag* was also seen in minor amounts whereas another Ag-peak at 8.13 min remains unknown. Most AgNPs remained free. AgNPs were only little associated with MT-1, the latter being split into two peak signals, whereas association with MT-2 was high. Only 15% of AgNPs remained unbound.We demonstrated CE hyphenated to the ICP-MS as promising and elegant technique to study AgNPs in biological systems. (C) 2018 Elsevier B.V. All rights reserved. AU - Michalke, B. AU - Vinković-Vrček, I.* C1 - 54193 C2 - 45431 CY - Po Box 211, 1000 Ae Amsterdam, Netherlands SP - 162-171 TI - Speciation of nano and ionic form of silver with capillary electrophoresis-inductively coupled plasma mass spectrometry. JO - J. Chromatogr. A VL - 1572 PB - Elsevier Science Bv PY - 2018 SN - 0021-9673 ER - TY - JOUR AB - Phenanthrene is present in numerous environmental media and serves as a model substrate for the biomonitoring of polycyclic aromatic hydrocarbon (PAH). PAH exposure studies are commonly focused on urinary metabolites, concentrations of which are dependent on absorption, biotransformation and excretion. Monitoring of unmetabolized PAHs in blood would allow more reliable exposure assessment, but requires invasive sampling and extensive sample preparation. We describe the analysis of phenanthrene in 1. μL capillary blood using thermal extraction (TE) combined with gas chromatography - mass spectrometry (GC-MS). Less invasive sampling of 1. μL capillary blood does not require the assistance of medical staff. Compared to previous studies, analysis time was improved significantly by TE due to minimization of sample preparation steps. The evaluate method was applied successfully to the monitoring of phenanthrene blood levels. This is the first report presenting the pharmacokinetics of unmetabolized PAHs in human. AU - Gruber, B. AU - Schneider, J. AU - Föhlinger, M. AU - Buters, J.T.M. AU - Zimmermann, R. AU - Matuschek, G. C1 - 50448 C2 - 42439 SP - 254-257 TI - A minimal-invasive method for systemic bio-monitoring of the environmental pollutant phenanthrene in humans: Thermal extraction and gas chromatography - mass spectrometry from 1 µl capillary blood. JO - J. Chromatogr. A VL - 1487 PY - 2017 SN - 0021-9673 ER - TY - JOUR AB - Vacuum ultraviolet (VUV) absorption spectroscopy was recently introduced as a new detection system for one, as well as comprehensive two-dimensional gas chromatography (GC×GC) and successfully applied to the analysis of various analytes in several matrices. In this study, its suitability for the analysis of breath metabolites was investigated and the impact of a finite volume of the absorption cell and makeup gas pressure was evaluated for volatile analytes in terms of sensitivity and chromatographic resolution. A commercial available VUV absorption spectrometer was coupled to GC×GC and applied to the analysis of highly polar volatile organic compounds (VOCs). Breath gas samples were acquired by needle trap micro extraction (NTME) during a glucose challenge and analysed by the applied technique. Regarding qualitative and quantitative information, the VGA-100 is compatible with common GC×GC detection systems like FID and even TOFMS. Average peak widths of 300ms and LODs in the lower ng range were achieved using GC×GC-VUV. Especially small oxygenated breath metabolites show intense and characteristic absorption patterns in the VUV region. Challenge responsive VOCs could be identified and monitored during a glucose challenge. The new VUV detection technology might especially be of benefit for applications in clinical research. AU - Gruber, B. AU - Gröger, T.M. AU - Harrison, D.* AU - Zimmermann, R. C1 - 49306 C2 - 41740 CY - Amsterdam SP - 141-146 TI - Vacuum ultraviolet absorption spectroscopy in combination with comprehensive two-dimensional gas chromatography for the monitoring of volatile organic compounds in breath gas: A feasibility study. JO - J. Chromatogr. A VL - 1464 PB - Elsevier Science Bv PY - 2016 SN - 0021-9673 ER - TY - JOUR AB - In the present work two different approaches, a semi-quantitative and a Derringer function approach, were developed to assist column selection for method development in targeted metabolomics. These approaches were applied in the performance assessment of three HILIC columns with different chemistries (an amide, a diol and a zwitterionic phase). This was the first step for the development of a HILIC UPLC-MS/MS method that should be capable to analyze a large number of polar metabolites. Two gradient elution profiles and two mobile phase pH values were tested for the analysis of multi-analyte mixtures. Acquired chromatographic data were firstly treated by a ratiometric, "semi-quantitative" approach which quantifies various overall analysis parameters (e.g. the percent of detected compounds, retentivity and resolved critical pairs). These parameters were used to assess chromatographic performance in a rather conventional/traditional and cumbersome/labor-intensive way. Secondly, a comprehensive and automated comparison of the three columns was performed by monitoring several well-known chromatographic parameters (peak width, resolution, tailing factor, etc.) using a lab-built programming script which calculates overall desirability utilizing Derringer functions. Derringer functions exhibit the advantage that column performance is ultimately expressed in an objective single and quantitative value which can be easily interpreted. In summary, results show that each column exhibits unique strengths in metabolic profiling of polar compounds. The applied methodology proved useful for the selection of the most effective chromatographic system during method development for LC-MS/MS targeted metabolomics, while it could further assist in the selection of chromatographic conditions for the development of multi-analyte methods. AU - Sampsonidis, I.* AU - Witting, M. AU - Koch, W. AU - Virgiliou, C.* AU - Gika, H.G.* AU - Schmitt-Kopplin, P. AU - Theodoridis, G.A.* C1 - 45603 C2 - 37427 CY - Amsterdam SP - 145-155 TI - Computational analysis and ratiometric comparison approaches aimed to assist column selection in hydrophilic interaction liquid chromatography-tandem mass spectrometry targeted metabolomics. JO - J. Chromatogr. A VL - 1406 PB - Elsevier Science Bv PY - 2015 SN - 0021-9673 ER - TY - JOUR AB - The application of ammonia acetate buffered liquid chromatography (LC) eluents is known to concomitantly lead to ion suppression when electrospray ionization mass spectrometry (ESI-MS) detection is used. In negative ESI mode, post column infusion of 2-(2-methoxyethoxy)ethanol (2-MEE) was shown in the literature to help to compensate this adverse effect occurring in reversed phase liquid chromatography mass spectrometry (RP-LC-MS) analyses. Here a setup of direct infusion and hydrophilic interaction chromatography (HILIC) post-column infusion experiments was established in order to investigate systematically the beneficial effects of 2-MEE. We demonstrate that, 2-MEE can help to improve ESI-MS sensitivity in HILIC too and reveal analyte structure specific behaviors. Our study indicates that 2-MEE especially improves ESI response for small and polar molecules. The ESI response of stable isotope labeled amino acids spiked into biological matrices increases up to 50-fold (i.e. D5-l-glutamic acid) when post column infusion of 2-MEE is applied. A non-targeted analysis of a pooled urine sample via HILIC-ESI-QTOF-MS supports this hypothesis. In direct infusion, the combined application of an ammonia acetate buffered solution together with 2-MEE results in an improved ESI response compared to a non-buffered solution. We observed up to 60-fold increased ESI response of l-lysine. We propose this effect is putatively caused by the formation of smaller ESI droplets and stripping of positive charge from ESI droplets due to evaporation of acetic acid anions. In summary, post-column infusion of 2-MEE especially enhances ESI response of small and polar molecules. Therefore it can be regarded as a valuable add-on in targeted or non-targeted metabolomic HILIC-MS studies since this method sets a focus on this molecule category. AU - Koch, W. AU - Forcisi, S. AU - Lehmann, R. AU - Schmitt-Kopplin, P. C1 - 31992 C2 - 34936 CY - Amsterdam SP - 209-216 TI - Sensitivity improvement in hydrophilic interaction chromatography negative mode electrospray ionization mass spectrometry using 2-(2-methoxyethoxy)ethanol as a post-column modifier for non-targeted metabolomics. JO - J. Chromatogr. A VL - 1361 PB - Elsevier Science Bv PY - 2014 SN - 0021-9673 ER - TY - JOUR AB - The growing scientific attention in the biological function of D-amino acids leads to an increasing analytical interest for enantiomeric amino acid separation, which is still very challenging due to the lack of sufficiently sensitive, high-throughput analytical methods that can cope with often occurring matrix interferences and very low D-amino acid concentrations. Here, enantioseparation can benefit from improved resolution and chromatographic speed offered by modern UHPLC techniques and the precision of MS detection. We developed a RP-UHPLC-QqToF-MS method using pre-column OPA/IBLC derivatization for very precise discrimination of amino acids enantiomers. The method shows a superb sensitivity with limits of detection in the range of several pmol/l. It has neither shown matrix inferences in the tested very complex biological matrices (serum, plasma, urine and gut) nor stability or racemisation problems. AU - Müller, C. AU - Fonseca, J.R. AU - Rock, T. AU - Krauss-Etschmann, S. AU - Schmitt-Kopplin, P. C1 - 28547 C2 - 33437 SP - 109-114 TI - Enantioseparation and selective detection of D-amino acids by ultra-high-performance liquid chromatography/mass spectrometry in analysis of complex biological samples. JO - J. Chromatogr. A VL - 1324 PB - Elsevier Science PY - 2014 SN - 0021-9673 ER - TY - JOUR AB - Multidimensional gas chromatography is an appropriate tool for the non-targeted and comprehensive characterisation of complex samples generated from combustion processes. Particulate matter (PM) emission is composed of a large number of compounds, including condensed semi-volatile organic compounds (SVOCs). However, the complex amount of information gained from such comprehensive techniques is associated with difficult and time-consuming data analysis. Because of this obstacle, two-dimensional gas chromatography still receives relatively little use in aerosol science [1-4]. To remedy this problem, advanced scripting algorithms based on knowledge-based rules (KBRs) were developed in-house and applied to GCxGC-TOFMS data. Previously reported KBRs and newer findings were considered for the development of these algorithms. The novelty of the presented advanced scripting tools is a notably selective search criterion for data screening, which is primarily based on fragmentation patterns and the presence of specific fragments. Combined with "classical" approaches based on retention times, a fast, accurate and automated data evaluation method was developed, which was evaluated qualitatively and quantitatively for type 1 and type 2 errors. The method's applicability was further tested for PM filter samples obtained from ship fuel combustion. Major substance classes, including polycyclic aromatic hydrocarbons (PAH), alkanes, benzenes, esters and ethers, can be targeted. This approach allows the classification of approximately 75% of the peaks of interest within real PM samples. Various conditions of combustion, such as fuel composition and engine load, could be clearly characterised and differentiated. AU - Weggler, B.A. AU - Gröger, T.M. AU - Zimmermann, R. C1 - 32348 C2 - 35011 CY - Amsterdam SP - 241-248 TI - Advanced scripting for the automated profiling of two-dimensional gas chromatography-time-of-flight mass spectrometry data from combustion aerosol. JO - J. Chromatogr. A VL - 1364 PB - Elsevier Science Bv PY - 2014 SN - 0021-9673 ER - TY - JOUR AB - Lipid profiling or lipidomics is currently applied in many different research fields. It refers to the global analysis of a samples lipid content using different analytical chemistry methods, with mass spectrometry as the mostly employed technology. We developed a comprehensive in-depth analysis method for the lipidome of the soil-dwelling nematode Caenorhabitis elegans, a widely used model organism. Four different columns were compared with a generic gradient and a novel sub-2-μm core-shell column, Waters Cortecs C18, showed superior performance in case of chromatographic peak characteristics, e.g. plate numbers and number of detected lipid features. Retention time deviation was generally less than 1% within one column and below 5% for columns from different batches. Intensity variation was lower than 30% for most detected features. Improved chromatographic separation showed enhanced resolution for isomeric lipids and allowed collection of highly detailed MS/MS spectra for lipid identification. In total 1304 lipid features were detected in positive ionization mode and 265 in negative mode. Lipids from different classes were annotated and MS/MS spectra obtained by data dependent fragmentation were used for identification purposes. AU - Witting, M. AU - Maier, T.V. AU - Garvis, S.* AU - Schmitt-Kopplin, P. C1 - 31853 C2 - 34810 CY - Amsterdam SP - 91-99 TI - Optimizing a ultrahigh pressure liquid chromatography-time of flight-mass spectrometry approach using a novel sub-2μm core-shell particle for in depth lipidomic profiling of Caenorhabditis elegans. JO - J. Chromatogr. A VL - 1359 PB - Elsevier Science Bv PY - 2014 SN - 0021-9673 ER - TY - JOUR AB - A common challenge for scientists working with animal tissue or human biopsy samples is the limitation of material and consequently, the difficulty to perform comprehensive metabolic profiling within one experiment. Here, we present a novel approach to simultaneously perform targeted and non-targeted metabolomics as well as lipidomics from one small piece of liver or muscle tissue by ultra-high performance liquid chromatography/mass spectrometry (UHPLC/MS) following a methyl tert-butyl ether (MTBE)-based extraction. Equal relative amounts of the resulting polar and non-polar fractions were pooled, evaporated and reconstituted in the appropriate solvent for UHPLC/MS analysis. This mix was comparable or superior in yield and reproducibility to a standard 80% methanol extraction for the profiling of polar and lipophilic metabolites (free carnitine, acylcarnitines and FFA). The mix was also suitable for non-targeted metabolomics, an easy measure to increase the metabolite coverage by 30% relative to using the polar fraction alone. Lipidomics was performed from an aliquot of the non-polar fraction. This novel strategy could successfully be applied to one mouse soleus muscle with a dry weight of merely 2.5 mg. By enabling a simultaneous profiling of lipids and metabolites with mixed polarity while saving material for molecular, biochemical or histological analyses, our approach may open up new perspectives toward a comprehensive investigation of small, valuable tissue samples. AU - Chen, S.L.* AU - Hoene, M. AU - Li, J.* AU - Li, Y.J.* AU - Zhao, X.J.* AU - Häring, H.-U. AU - Schleicher, E.D. AU - Weigert, C. AU - Xu, G.W.* AU - Lehmann, R. C1 - 26273 C2 - 32167 SP - 9-16 TI - Simultaneous extraction of metabolome and lipidome with methyl tert-butyl ether from a single small tissue sample for ultra-high performance liquid chromatography/mass spectrometry. JO - J. Chromatogr. A VL - 1298 PB - Elsevier Science PY - 2013 SN - 0021-9673 ER - TY - JOUR AB - The present review gives an introduction into the concept of metabolomics and provides an overview of the analytical tools applied in non-targeted metabolomics with a focus on liquid chromatography (LC). LC is a powerful analytical tool in the study of complex sample matrices. A further development and configuration employing Ultra-High Pressure Liquid Chromatography (UHPLC) is optimized to provide the largest known liquid chromatographic resolution and peak capacity. Reasonably UHPLC plays an important role in separation and consequent metabolite identification of complex molecular mixtures such as bio-fluids. The most sensitive detectors for these purposes are mass spectrometers. Almost any mass analyzer can be optimized to identify and quantify small pre-defined sets of targets; however, the number of analytes in metabolomics is far greater. Optimized protocols for quantification of large sets of targets may be rendered inapplicable. Results on small target set analyses on different sample matrices are easily comparable with each other. In non-targeted metabolomics there is almost no analytical method which is applicable to all different matrices due to limitations pertaining to mass analyzers and chromatographic tools. The specifications of the most important interfaces and mass analyzers are discussed. We additionally provide an exemplary application in order to demonstrate the level of complexity which remains intractable up to date. The potential of coupling a high field Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (ICR-FT/MS), the mass analyzer with the largest known mass resolving power, to UHPLC is given with an example of one human pre-treated plasma sample. This experimental example illustrates one way of overcoming the necessity of faster scanning rates in the coupling with UHPLC. The experiment enabled the extraction of thousands of features (analytical signals). A small subset of this compositional space could be mapped into a mass difference network whose topology shows specificity toward putative metabolite classes and retention time. AU - Forcisi, S. AU - Moritz, F. AU - Kanawati, B. AU - Tziotis, D. AU - Lehmann, R.* AU - Schmitt-Kopplin, P. C1 - 24878 C2 - 31709 SP - 51-65 TI - Liquid chromatography-mass spectrometry in metabolomics research: Mass analyzers in ultra high pressure liquid chromatography coupling. JO - J. Chromatogr. A VL - 1292 PB - Elsevier Science PY - 2013 SN - 0021-9673 ER - TY - JOUR AB - The goal of this paper is to demonstrate the separation and detection capability of eco-friendly micro-TLC technique for the classification of spirulina and selected herbs from pharmaceutical and food products. Target compounds were extracted using relatively low-parachor liquids. A number of the spirulina samples which originated from pharmaceutical formulations and food products, were isolated using a simple one step extraction with small volume of methanol, acetone or tetrahydrofuran. Herb samples rich in chlorophyll dyes were analyzed as reference materials. Quantitative data derived from micro-plates under visible light conditions and after iodine staining were explored using chemometrics tools including cluster analysis and principal components analysis. Using this method we could easily distinguish genuine spirulina and non-spirulina samples as well as fresh from expired commercial products and furthermore, we could identify some biodegradation peaks appearing on micro-TLC profiles. This methodology can be applied as a fast screening or fingerprinting tool for the classification of genuine spirulina and herb samples and in particular may be used commercially for the rapid quality control screening of products. Furthermore, this approach allows low-cost fractionation of target substances including cyanobacteria pigments in raw biological or environmental samples for preliminary chemotaxonomic investigations. Due to the low consumption of the mobile phase (usually less than 1 mL per run), this method can be considered as environmentally friendly analytical tool, which may be an alternative for fingerprinting protocols based on HPLC machines and simple separation systems involving planar micro-fluidic or micro-chip devices. AU - Zarzycki, P.K.* AU - Zarzycka, M.B.* AU - Clifton, V.L.* AU - Adamski, J. AU - Głód, B.K.* C1 - 3758 C2 - 28887 SP - 5694-5704 TI - Low-parachor solvents extraction and thermostated micro-thin-layer chromatography separation for fast screening and classification of spirulina from pharmaceutical formulations and food samples. JO - J. Chromatogr. A VL - 1218 IS - 33 PB - Elsevier PY - 2011 SN - 0021-9673 ER - TY - JOUR AB - The development, optimization and validation of a liquid chromatography-atmospheric pressure photoionization tandem mass spectrometric (LC-APPI/MS/MS) method for the determination of 15 azaarenes (4-azafluorene, benzo[h] and -[f]quinoline, phenanthridine, acridine, 1-azafluoranthene, 4-azapyrene, benz[a]- and -[c]acridine, -10-azabenzo[a]pyrene, 7,9- and 7,10-dimethylbenz[c]acridine, dibenz[a,j]-,-[c,h] and [a,i]acridine) in airborne particulate matter is described. Each compound was detected and quantified operating in multiple reaction monitoring mode. Extraction of azaarenes was achieved using accelerated solvent extraction (ASE) with dichlormethane/methanol (50/50, v/v). After extraction, no additional clean-up procedure like solid phase or liquid/liquid extraction was necessary. Limits of quantification (S/N x 10) ranged from 0.2 pg/mu l, matrix dependent recoveries were between 57% and 94%, with relative standard deviations from 8% to 17%. Applicability of the method was demonstrated analyzing 10 samples of particulate matter (PM2.5) collected in winter 2008. In all samples dimethylbenz[c]acridines as well as dibenzacridines were below the limit of quantification, concentration of the remaining analytes were in the range from 0.002 ng/m(3) to 0.356 ng/m(3). AU - Lintelmann, J. AU - Franca, M.H. AU - Hübner, E. AU - Matuschek, G. C1 - 63 C2 - 27092 SP - 1636-1646 TI - A liquid chromatography-atmospheric pressure photoionization tandem mass spectrometric method for the determination of azaarenes in atmospheric particulate matter. JO - J. Chromatogr. A VL - 1217 IS - 10 PB - Elsevier Science B.V. PY - 2010 SN - 0021-9673 ER - TY - JOUR AB - In this work, the potential of combining capillary electrophoresis-time-of-flight-mass spectrometry (CE-TOF-MS) and Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) for metabolomics of genetically modified organisms (GMOs) is demonstrated. Thus, six different varieties of maize, three of them transgenic(PR33P66 Bt, Tietar Bt and Aristis Bt) and their corresponding isogenic lines (PR331366, Tietar and Aristis) grown under the same field conditions, were analyzed. Based on the ultrahigh resolution and remarkable mass accuracy provided by the 12-T FT-ICR-MS it was possible to directly analyze a good number of metabolites whose identity could be proposed based on their specific isotopic pattern. For identification of metabolite isomers, CE-TOF-MS was also used combining the information on nominal mass with electrophoretic mobility corroborating in that way the identity of several new biomarkers. Furthermore, PLE extractions were evaluated in order to establish selective extraction as an additional criterion to obtain useful information in maize metabolomics. Differences in the metabolite levels were found between the three transgenic maize varieties compared with their wild isogenic lines in some specific metabolic pathways. To our knowledge, this is the first time that an approach as the one presented in this work (pressurized liquid extraction + FT-ICR-MS + CE-TOF-MS) is shown for a metabolomic study. AU - Leon, C.* AU - Rodriguez-Meizoso, I.* AU - Lucio, M.* AU - Garcia-Canas, V.* AU - Ibanez, E.* AU - Schmitt-Kopplin, P. AU - Cifuentes, A.* C1 - 415 C2 - 26775 CY - Amsterdam SP - 7314-7323 TI - Metabolomics of transgenic maize combining Fourier transform-ion cyclotron resonance-mass spectrometry, capillary electrophoresis-mass spectrometry and pressurized liquid extraction. JO - J. Chromatogr. A VL - 1216 IS - 43 PB - Elsevier PY - 2009 SN - 0021-9673 ER - TY - JOUR AB - The chemical profiling of illicit drugs is a complex process. The results are affected by many different factors such as sample size, the sample processing conditions, the used analytical technique as well as the statistics that are applied. Within this proof-of-concept study, which was done in cooperation with the German Federal Criminal Police Office (Bundeskriminalamt, BKA), the adaptability of comprehensive two-dimensional (2D) gas chromatography (GCxGC) combined with a pixel-based chemometric data processing method is demonstrated. Samples of heroin and cannabis are extracted and analyzed with GCxGC-TOF-MS (time-of-flight mass spectrometry) and GCxGC-FID (flame ionization detection). The obtained second-order data are then used to identify possible marker compounds for the discrimination of the samples according to their chemical profile. The pixel-based chemometric process includes preprocessing steps (background correction, alignment of chromatograms and normalization) followed by an adaptation of hierarchical clustering to identify chemically similar samples, and finally a subsequent calculation of Fisher criterion based on the found clustering in order to identify promising marker compounds. The results of the pixel-based data analysis are compared to a limited peak-based study for cannabis and to a well-established standard method for the chemical profiling of heroin. AU - Gröger, T.M. AU - Schäffer, M. AU - Pütz, M.* AU - Ahrens, B. AU - Drew, K.* AU - Eschner, M.* AU - Zimmermann, R. C1 - 489 C2 - 25707 SP - 8-16 TI - Application of two-dimensional gas chromatography combined with pixel-based chemometric processing for the chemical profiling of illicit drug samples. JO - J. Chromatogr. A VL - 1200 IS - 1 PB - Elsevier PY - 2008 SN - 0021-9673 ER - TY - JOUR AB - Mass spectrometry (MS) with soft ionisation techniques (i.e. ionisation without fragmentation of the analyte molecules) for gaseous samples exhibits interesting analytical properties for direct analysis applications (i.e. direct inlet mass spectrometric on-line monitoring) as well as mass spectrometric detection method for gas chromatography (GC-MS). Commonly either chemical ionisation (CI) or field ionisation (FI) is applied as soft ionisation technology for GC-MS. An interesting alternative to the CI and FI technologies methods are photo-ionisation (PI) methods. PI overcomes some of the limitations of CI and FI and furthermore add some unique analytical properties. The resonance enhanced multi-photon ionisation (REMPI) method uses intense UV-laser pulses (wavelength range approximately 350-193 nm) for highly selective, sensitive and soft ionisation of predominately aromatic compounds. The single photon ionisation (SPI) method utilises VUV light (from lamps or laser sources, wavelengths range approximately 150-110 nm) can be used for a universal soft ionisation of organic molecules. In this article the historical development as well as the current status and concepts of gas chromatography hyphenated to photo-ionisation mass spectrometry are reviewed. AU - Zimmermann, R. AU - Welthagen, W. AU - Gröger, T.M. C1 - 2344 C2 - 25309 SP - 296-308 TI - Photo-ionisation mass spectrometry as detection method for gas chromatography. Optical selectivity and multidimensional comprehensive separations. JO - J. Chromatogr. A VL - 1184 IS - 1-2 PB - Elsevier PY - 2008 SN - 0021-9673 ER - TY - JOUR AB - Derivatives of N-acylhomoserine lactones (HSLs) with different alkanoyl side chains occur as quorum or diffusion sensing molecules in Gram-negative bacteria and their quantitative chemical analysis became important as a possible way to follow regulation processes of their pathogenicity towards plants and animals. The lactone-ring of HSLs is chemically and biologically not stable: the corresponding serines can be formed in alkaline conditions and these may presumably behave inactive for the biological system. A fast and MS compatible liquid chromatographic method applying high pressure (ultra performance liquid chromatography) with diode array detection was optimized for the rapid quantitative determination of HSLs and their corresponding hydrolysis products. The technique was used to follow and model the hydrolysis reactions of HSLs as function of pH under controlled conditions. Moreover, the method could be triggered to allow a confirmation in the assignment of the potential HSLs in real samples by analysis of the real samples before and after hydrolysis. Quantitative performance characteristics and the character of the hydrolysis reaction were studied as well. The optimized method was successfully applied to a bacterial culture supernatant real sample containing HSLs. AU - Englmann, M. AU - Fekete, A. AU - Kuttler, C. AU - Frommberger, M. AU - Li, X. AU - Gebefügi, I. AU - Fekete, J.* AU - Schmitt-Kopplin, P. C1 - 2445 C2 - 24560 SP - 184-193 TI - The hydrolysis of unsubstituted N-acylhomoserine lactones to their homoserine metabolites. Analytical approaches using ultra performance liquid chromatography. JO - J. Chromatogr. A VL - 1160 IS - 1-2 PB - Elsevier PY - 2007 SN - 0021-9673 ER - TY - JOUR AB - Comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOF-MS) is useful in analyzing complex samples, such as the semi-volatile organic compounds (SVOC) in daily aerosol samples collected in Augsburg, Germany. For efficient routine analysis, a partial classification system based on mass spectra has been proposed to group compounds into substance classes. Classifiers based on fragmentation patterns, retention time, and spectral transformations are incorporated into software scripts for automated classification. Fragmentation pattern rules are also applied to an aerosol sample analyzed using direct thermal desorption (DTD)–GC × GC–TOF-MS and a non-traditional column combination. AU - Vogt, L.* AU - Gröger, T.M. AU - Zimmermann, R. C1 - 1064 C2 - 24414 SP - 2-12 TI - Automated compound classification for ambient aerosol sample separations using comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry. JO - J. Chromatogr. A VL - 1150 IS - 1-2 PB - Elsevier PY - 2007 SN - 0021-9673 ER - TY - JOUR AB - Soft laser photo-ionization mass spectroemtry is presented as a separation dimension hyphenated with gas chromatographic techniques. Single photon ionization (SPI) is a universal soft ionization method which ionizes organic molecules with an ionization potential below 10.5 eV if 118 nm laser radiation is used. The inherently soft ionization of photo ionization techniques can further be utilized together with gas chromatography as a comprehensive two-dimensional separation method (GC × MS), using the GC retention time as first separation dimension and the molecular mass as second separation dimension. Some GC × MS chromatograms of diesel petroleum samples using SPI are presented and discussed. Finally, it is demonstrated that the coupling of soft SPI mass spectrometry with comprehensive two-dimensional gas chromatography (GC × GC) provides a three-dimensional separation technique (GC × GC × SPI-MS). AU - Welthagen, W.* AU - Mitschke, S.* AU - Mühlberger, F. AU - Zimmermann, R. C1 - 4987 C2 - 24417 SP - 54-61 TI - One-dimensional and comprehensive two-dimensional gas chromatography coupled to soft photo ionization time-of-flight mass spectrometry: A two- and three-dimensional separation approach. JO - J. Chromatogr. A VL - 1150 IS - 1-2 PB - Elsevier PY - 2007 SN - 0021-9673 ER - TY - JOUR AB - A robust method based on solid-phase extraction (SPE) followed by ultra high pressure liquid chromatography (with trade name of Ultra Performance Liquid Chromatography: UPLC; Waters, Milford, MA, USA) is proposed for the determination of five derivatives of N-acylhomoserine lactones (AHLs) that play a biological role as signal molecules of several gram-negative bacteria. Different commercial SPE cartridges were tested for sample extraction, clean-up and preconcentration. Since the sample matrix was a complex growth media, careful optimization of the SPE with respect to washing procedure, elution solvent and sample solvent was necessary. No sample loss was observed when up to 100 mL spiked full media was added onto the cartridge. Applying UPLC for the determination of AHLs, the performance characteristics of the method showed good separation efficiency and high speed. In order to demonstrate the applicability of the method, supernatants with the known AHL producer Burkholderia cepacia LA3 grown in different media were investigated. Additionally, the method was successfully used for the degradation/uptake study of AHLs from a liquid matrix in which barley was grown under controlled condition. © 2006 Elsevier B.V. All rights reserved. AU - Li, X. AU - Fekete, A. AU - Englmann, M. AU - Götz, C. AU - Rothballer, M. AU - Frommberger, M. AU - Buddrus, K. AU - Fekete, J.* AU - Cai, C.* AU - Schröder, P. AU - Hartmann, A. AU - Chen, G.* AU - Schmitt-Kopplin, P. C1 - 5102 C2 - 24210 CY - Amsterdam SP - 186-193 TI - Development and application of a method for the analysis of N-acylhomoserine lactones by solid-phase extraction and ultra high pressure liquid chromatography. JO - J. Chromatogr. A VL - 1134 IS - 1-2 PB - Elsevier PY - 2006 SN - 0021-9673 ER - TY - JOUR AB - A high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) method with a rapid and simple sample preparation was optimized and validated for the determination of phenanthrene-9, 10-dione, chrysene-5,6-dione, benzo[a]pyrene- 1,6-dione, benzo[a]pyrene-3,6-dione, benzo[a]pyrene-4,5-dione, benzo[a]pyrene-6,12-dione, benzo[a]pyrene-7,8-dione, benzo[a]pyrene-11,12-dione and 6-oxo-7-oxa-benzo[a]pyrene in particulate matter. The mass spectrometer was operated in the multiple reaction monitoring (MRM) mode leading to high sensitivity and selectivity. The limits of quantification (S/N = 10) ranged from ca. 0.1 pg/mu l to ca. 5.8 pg/mu l and matrix dependent recoveries varied between 49 and 92%. The applicability of the LC-MS/MS method was shown by the analysis of particulate matter (PM2.5) collected during the course of 2005 in the Munich area, Germany. All oxy-PAHs determined exhibited higher mean and peak concentrations in the winter months compared to the concentration levels in the warmer season. AU - Lintelmann, J. AU - Fischer, K. AU - Matuschek, G. C1 - 5325 C2 - 23937 SP - 241-247 TI - Determination of oxygenated polycyclic aromatic hydrocarbons in particulate matter using high-performance liquid chromatography-tandem mass spectrometry. JO - J. Chromatogr. A VL - 1133 IS - 1-2 PY - 2006 SN - 0021-9673 ER - TY - JOUR AU - Zhang, X.* AU - Martens, D.* AU - Krämer, P.M. AU - Kettrup, A.* AU - Liang, X.* C1 - 1522 C2 - 23458 SP - 84-90 TI - Development and application of a sol-gel immunosorbent-based method for the determination of isoproturon in surface water. JO - J. Chromatogr. A VL - 1102 PY - 2006 SN - 0021-9673 ER - TY - JOUR AU - Zhang, X.* AU - Martens, D.* AU - Krämer, P.M. AU - Kettrup, A.* AU - Liang, X.* C1 - 5326 C2 - 23938 SP - 112-118 TI - On-line immunoaffinity column-liquid chromatography-tandem mass spectrometry method for trace analysis of diuron in wastewater treatment plant effluent sample. JO - J. Chromatogr. A VL - 1133 PY - 2006 SN - 0021-9673 ER - TY - JOUR AU - Shellie, R.A.* AU - Welthagen, W. AU - Zrostlikova, J.* AU - Spranger, J.* AU - Ristow, M.* AU - Fiehn, O.* AU - Zimmermann, R. C1 - 2306 C2 - 22908 SP - 83-90 TI - Statistical methods for comparing comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry results: Metabolomic analysis of mouse tissue extracts. JO - J. Chromatogr. A VL - 1086 PY - 2005 SN - 0021-9673 ER - TY - JOUR AU - Hauler, T.E. AU - Boesl, U.* AU - Kaesdorf, S.* AU - Zimmermann, R. C1 - 4647 C2 - 22121 SP - 39-49 TI - Mobile resonance enhanced multiphoton ionisation-time-of-flight mass spectrometer with a novel hybrid laser desorption/molecular beam ion source for rapid detection of aromatic trace compounds from gas phase and solid samples. JO - J. Chromatogr. A VL - 1058 PY - 2004 SN - 0021-9673 ER - TY - JOUR AU - Michalke, B. C1 - 1396 C2 - 22240 SP - 203-208 TI - Selenium speciation in human serum of cystic fibrosis patients compared to serum from healthy persons. JO - J. Chromatogr. A VL - 1058 PY - 2004 SN - 0021-9673 ER - TY - JOUR AU - Michalke, B. C1 - 3784 C2 - 21985 SP - 69-76 TI - Manganese speciation using capillary electrophoresis-ICP-mass spectrometry. JO - J. Chromatogr. A VL - 1050 PY - 2004 SN - 0021-9673 ER - TY - JOUR AU - Ping, G.* AU - Zhang, L.* AU - Zhang, W.* AU - Schmitt-Kopplin, P. AU - Kettrup, A. AU - Zhang, Y.* C1 - 2580 C2 - 21780 SP - 265-270 TI - Separation of acidic and basic compounds in capillary electrochromatography with polymethacrylate-based monolithic columns. JO - J. Chromatogr. A VL - 1035 PY - 2004 SN - 0021-9673 ER - TY - JOUR AU - Hoque, E. AU - Wolf, M. AU - Teichmann, G. AU - Peller, E. AU - Schimmack, W. AU - Buckau, G.* C1 - 10097 C2 - 21304 SP - 97-105 TI - Influence of ionic strenght and organic modifier concentrations on characterization of aquatic fulvic and humic acids by high-performance size-exclusion chromatography. JO - J. Chromatogr. A VL - 1017 PY - 2003 SN - 0021-9673 ER - TY - JOUR AU - Nischwitz, V. AU - Michalke, B. AU - Kettrup, A. C1 - 10096 C2 - 21172 SP - 223-234 TI - Speciation of Pt(II) and Pt(IV) in spiked extracts from road dust using on-line liquid chromatography-inductively coupled plasma mass spectrometry. JO - J. Chromatogr. A VL - 1016 PY - 2003 SN - 0021-9673 ER - TY - JOUR AU - Schmitt-Kopplin, P. AU - Junkers, J. C1 - 10095 C2 - 20998 SP - 1-20 TI - Capillary zone electrophoresis of natural organic matter. JO - J. Chromatogr. A VL - 998 PY - 2003 SN - 0021-9673 ER - TY - JOUR AU - Welthagen, W. AU - Schnelle-Kreis, J.* AU - Zimmermann, R. C1 - 10098 C2 - 21355 SP - 233-249 TI - Search criteria and rules for comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry analysis of airborne particulate matter. JO - J. Chromatogr. A VL - 1019 PY - 2003 SN - 0021-9673 ER - TY - JOUR AB - The retention factors (k) of 104 hydrophobic organic chemicals (HOCs) were measured in soil column chromatography (SCC) over columns filled with three naturally occurring reference soils and eluted with Milli-Q water. A novel method for the estimation of soil organic partition coefficient (K-oc) was developed based on correlations with k in soil/water systems. Strong log K-oc versus log k correlations (r>0.96) were found. The estimated K-oc values were in accordance with the literature values with a maximum deviation of less than 0.4 log units. All estimated K-oc values from three soils were consistent with each other. The SCC approach is promising for fast screening of a large number of chemicals in their environmental applications. AU - Xu, F.* AU - Liang, X.* AU - Lin, B.* AU - Schramm, K.-W. AU - Kettrup, A. C1 - 10099 C2 - 20398 SP - 7-16 TI - Estimation of soil organic partition coefficients : from retention factors measured by soil column chromatography with water as eluent. JO - J. Chromatogr. A VL - 968 PB - Elsevier PY - 2002 SN - 0021-9673 ER - TY - JOUR AU - Whang, W.* AU - Zhang, L. AU - Ping, G.* AU - Zhang, Y.* AU - Kettrup, A. C1 - 10100 C2 - 20144 SP - 277-282 TI - Migration of neutral solutes by double stepwise gradient elution in capillary electrochromatography. JO - J. Chromatogr. A VL - 922 PY - 2001 SN - 0021-9673 ER - TY - JOUR AB - he separation of amygdalin, prunasin and their isomers neoamygdalin and sambunigrin could be achieved with micellar capillary electrophoresis (MEKC). The two isomers were obtained in alkaline conditions and were produced in less than 15 min at pH 11.0. The developed methods showed a good selectivity in the separation of the isomers only in the presence of SDS micelles. The working pH was optimized to allow best resolution and quantitative analysis of these compounds, With a linear calibration over an injection time from 1 to 20 s, the detection limit was found to be in the range of 5 mu M (S/N=3; 20 a injection time). Two pH buffer systems (pH 5.2 and pH 9.1) were chosen to confirm the peak attributions of the compounds in the apple and peach seeds samples. Sambunigrin was found in both apple and peach seeds but could not be quantified because of missing standards. Prunasin and amygdalin were not found in the apple sample, while they were quantified in the peach seeds in concentrations of 50 mu g/g and 90 mu g/g (dry weight), respectively. AU - Campa, C.* AU - Schmitt-Kopplin, P. AU - Cataldi, T.R.I.* AU - Bufo, S.A.* AU - Freitag, D. AU - Kettrup, A. C1 - 10094 C2 - 19148 SP - 95-100 TI - Analysis of cyanogenic glycosides by micellar capillary electrophoresis. JO - J. Chromatogr. A VL - 739 PB - Elsevier PY - 2000 SN - 0021-9673 ER - TY - JOUR AU - Menzinger, F. AU - Schmitt-Kopplin, P. AU - Freitag, D. AU - Kettrup, A. C1 - 21396 C2 - 19514 SP - 45-67 TI - Analysis of agrochemicals by capillary electrophoresis. JO - J. Chromatogr. A VL - 891 PY - 2000 SN - 0021-9673 ER - TY - JOUR AU - Wilhelm, M. AU - Matuschek, G. AU - Kettrup, A. C1 - 21280 C2 - 19392 SP - 171-181 TI - Determination of basic nitrogen-containing polynuclear aromatic hydrocarbons formed during thermal degradation of polymers by high-performance liquid chromatography-fluorescence detection. JO - J. Chromatogr. A VL - 878 PY - 2000 SN - 0021-9673 ER - TY - JOUR AU - Michalke, B. AU - Schramel, P. C1 - 20838 C2 - 18872 SP - 341-348 TI - Antimony speciation in environmental samples by interfacing capillary electrophoresis on-line to an inductively coupled plasma mass spetrometer. JO - J. Chromatogr. A VL - 834 PY - 1999 SN - 0021-9673 ER - TY - JOUR AU - Schmitt-Kopplin, P. AU - Burhenne, J.* AU - Freitag, D. AU - Spiteller, M.* AU - Kettrup, A. C1 - 20855 C2 - 18909 SP - 253-265 TI - Development of capillary electrophoresis methods for the analysis of fluorquinolones and application to the study of the influence of humic substances on their photodegradation in aqueous phase. JO - J. Chromatogr. A VL - 837 PY - 1999 SN - 0021-9673 ER - TY - JOUR AB - An optimized method for the determination of substances occurring in auxin metabolism and L-tryptophan (TRP) catabolism was developed. It is based on solid-phase extraction (SPE), two isocratic reversed-phase high-performance liquid chromatographic (HPLC) separations at different liquid phase conditions and the simultaneous detection of fluorescence and UV absorbance at different wavelengths. Advantages of the proposed method are: the solvent (ethanol) and liquid phase (containing 2-propanol) provide optimum stability and selectivity; almost no toxic wastes are produced; no time-consuming liquid-liquid extractions (LLE), derivatization procedures or column re-equilibration (obligatory for gradient systems) are necessary, no need for antioxidants, ion-pair or derivatization reagents; recovery rates of the SPE system are superior to LLE effeciencies; high sensitivity, selectivity and identification capacity are provided by the proposed HPLC and detection system. By measuring various chromatographic and spectral parameters simultaneously, the determination reliability is improved. The characteristic chromatographic and spectral data for selected indole derivatives and TRP catabolites are presented. In samples from two different soils that were tested with the proposed method, the actual contents of TRP were 1.4 and 5.8 μg/g dry soil. In addition, traces of indole-3-acetic acid (IAA) could be detected. When TRP was added, IAA was the predominant catabolite in both soils, and reached values of 2.9 and 8.0 μg/g dry soil. In addition to IAA, indole-3-ethanol, indole-3-aldehyde, indole-3-carboxylic acid, indole-3-lactic acid, anthranilic acid and traces of indole-3-acetamide were identified and determined. AU - Lebuhn, M. AU - Hartmann, A. C1 - 40372 C2 - 40093 SP - 255-266 TI - Method for the determination of indole-3-acetic acid and related compounds of L-tryptophan catabolism in soils. JO - J. Chromatogr. A VL - 629 IS - 2 PY - 1993 SN - 0021-9673 ER - TY - JOUR AB - A coupled-column high-performance liquid chromatographic system for integrated, on-line sample processing and the determination of free and conjugated 1-hydroxypyrene in urine has been developed. The method is based on a "tailor-made" copper phthalocyanine-modified porous-glass precolumn packing material, which allows a direct and repeated injection of urine samples and a selective enrichment of trace amounts of particular components. The fully automated method has a low detection limit (0.01 pmol), a quantitative and matrix-independent recovery and a highly reliability, as shown by an interlaboratory comparison of methods. AU - Boos, K.S.* AU - Lintelmann, J. AU - Kettrup, A. C1 - 40509 C2 - 38732 SP - 189-194 TI - Coupled-column high-performance liquid chromatographic method for the determination of 1-hydroxypyrene in urine of subjects exposed to polycyclic aromatic hydrocarbons. JO - J. Chromatogr. A VL - 600 IS - 2 PY - 1992 SN - 0021-9673 ER - TY - JOUR AB - Rate equations are given for film diffusion-controlled, differentially small ion-exchange processes in a finite solution volume. Two possibilities of performing differential ion-exchange reactions were considered: (1) reactions in which, independent of the initial ionic composition of the sample, the same small amount of counter ions is added, and (2) reactions in which, depending on the initial ionic composition of the sample, the amount of counter ions added is adjusted so as always to yield the same differential conversion of the sample. The theory shows in which way the rate of a differential ion-exchange process, which may involve ions of arbitrary valency, depends on the diffusion coefficients of the ions in the film, on the selectivity of the ion exchanger, on the initial ionic composition of the sample and on the extent of each differential reaction. It is shown that at any given initial ionic composition of the sample, the ratio of the initial rate of the forward to that of the corresponding reverse differential ion-exchange process is independent of the diffusion coefficients of the ions. AU - Bunzl, K.W. C1 - 41874 C2 - 35513 SP - 169-180 TI - Kinetics of differential ion-exchange processes in a finite solution volume. JO - J. Chromatogr. A VL - 102 IS - C PY - 1974 SN - 0021-9673 ER -