Comparison of gas and liquid chromatography coupled to mass spectrometry for the residue analysis of pesticides in organges

Summary Liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination of eight pesticides in oranges. Seven of the selected pesticides, chlorpyriphos, chlorpyriphos-methyl, imazalil, α and β-endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabendazole, can only be directly determined by LC. Primary ions [M-H]⁻ or [M-Cl+O]⁻ are obtained using LC-APCI-MS in negative ionization (NI) mode. In contrast, a high degree of fragmentation is reported with GC-MS. Both techniques were applied to oranges, which had been previously extracted with ethyl acetate and anhydrous sodium sulphate. The data indicate equivalent detection limits that range from 0.01 to 0.1 mgkg⁻¹ and similar degree of specificity. Mean recoveries ranged from 82% for α-endosulfant to 96% for imazalil, with relative standard deviation ranging from 7 to 17%.     

Comprehensive two-dimensional liquid chromatography coupled with mass spectrometry

In this review, instrumental aspects of comprehensive two-dimensional liquid chromatography coupled with mass spectrometry are presented. The milestones of LC×LC are briefly summarized. Instrument configuration, selection of experimental conditions, the different interfaces used in the system and the current applications of LC×LC–MS systems are described.     

Direct analysis of industrial oligoglycerols by liquid chromatography with evaporative light-scattering detection and mass spectrometry

Summary A liquid chromatographic method has been developed for analysis of industrial polyglycerols, precursors of polyglycerol fatty esters, which are non-ionic surfacetants. The method utilizes two complementary chromatographic systems: porous graphitic carbon and an aminopropyl polymer with an acetonitrile-water mixture as mobile phase. Detection of these non-UV absorbing compounds was effected by means of evaporative light-scattering detection. Their structures were determined by comparison of their retention with that of synthesized standards, and by mass spectrometry.     

Molecular-shape recognition of polycyclic aromatic hydrocarbons in reversed phase liquid chromatography

Summary The molecular-shape recognition of polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase high-performance liquid chromatography. The examined stationary phases were phenyl-, diphenyl-, triphenyl- and benzyl-bonded silicas. The results of regression analysis inidcated that triphenylsilica is the best packing material to recognize the difference in the molecular-shape of structural isomers. This fact was confirmed by the separation of 4-ring isomers.     

Analysis of oligonucleotides using coupled high performance liquid chromatography-electrospray mass spectrometry

Summary Improved HPLC and ESMS conditions have been established, allowing the separation and analysis of oligodesoxyribonucleotides by coupled HPLC-ESMS.     

The evaluation of “reversed phase” high-performance liquid chromatography packing materials

Summary For the evaluation of reversed phase packing materials a mixture of acetylacetone, I-nitronaphthalene and naphthalene is proposed. This will reveal the usual optimum kinetic chromatographic parameters (the naphthalene peak), the degree of activity or endcapping status of the column (the ratio of the I-nitronaphthalene and naphthalene retention times) and trace metal activity (the shape and intensity of the acetylacetone peak).     

Marked differences between acetonitrile/water and methanol/water mobile phase systems on the thermodynamic behavior of benzodiazepines in reversed phase liquid chromatography

Summary Two different methods were used to determine the separation factor α at different temperatures and the Gibbs-Helmholtz parameters (Δ(ΔH), Δ(ΔS)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of lnα versus 1/T. We first studied each factor (fraction of water ϕ in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes in Δ(ΔH) and Δ(ΔS) in relation to a volume fraction of water ϕ in an ACN/water mixture were examined. In the ACN/water system, Δ(ΔH) was fairly constant in the acetonitrile region of ϕ≤0.52 and appears to be a roughly linear function of ϕ for ϕ≥0.52. In this system Δ(ΔS) is approximately a parabolic function of ϕ with an optimum at ϕ≊0.52. The retention mechanism of ten benzodiazepines was found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44 °C gave the most efficient separation conditions in the ACN/water mixture.     

Marked differences between acetonitrile/water and methanol/water mobile phase systems on the thermodynamic behavior of benzodiazepines in reversed phase liquid chromatography

Summary Two different methods were used to determine the separation factor at different temperatures and the Gibbs-Helmholtz parameters ((H), (S)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of ln versus 1/T. We first studied each factor (fraction of water in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes in (H) and (S) in relation to a volume fraction of water in an ACN/water mixture were examined. In the ACN/water system, (H) was fairly constant in the acetonitrile region of 0.52 and appears to be a roughly linear function of for 0.52. In this system (S) is approximately a parabolic function of with an optimum at 0.52. The retention mechanism of ten benzodiazepines was found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44°C gave the most efficient separation conditions in the ACN/water mixture.     

Determination of furosine in milk samples by ion-pair reversed phase liquid chromatography

Summary An ion-pair, reversed-phase, liquid chromatographic procedure using UV detection for quantitation of furosine is described. The standard plot was linear (r>0.999) over a 5 ng range. An authentic synthesised sample of furosine was used for calibration. Commerical milk samples were analyzed by the described procedure.     

啤酒中单糖的衍生化HPLC-ESI-MS测定方法研究

单糖类样品在溶液中非常稳定,难于离子化,不适合于进行ESI-MS检测。采用1-苯基-3-甲基-5-吡唑啉酮(PMP)将糖类物质衍生化,HPLC-ESI-MS在线联用,选择性离子扫描方式对几种啤酒样品中的5种单糖进行了分离检测。检出限可达到80pg。     

Retention and column efficiency in reversed phase liquid chromatography as a function of pH for optimization purposes

Summary The effects of pH on both the solute retention and the peak shape of ionogenic compounds are studied in order to propose accurate models for pH optimization purposes. Several mathematical models (theoretical and empirical) for describing the variation of the retention factor versus pH are compared within different pH ranges. Limits of such models used for optimizing the pH by requiring only 3 preliminary experimental runs, are discussed in terms of deviations (≤±5%) of predicted retention times from experimental retention times. An original procedure is developed for selecting the most convenient retention model, from a given set of three retention data. This set is also applied to modeling the variation of both peak width and peak asymmetry with mobile phase pH conditions. Such a procedure is demonstrated as helpful for the separation of ionogenic solutes by considering mobile phase pH as an additional variable that can be useful during optimization procedures.     

The application of high performance liquid chromatography, coupled to nuclear magnetic resonance spectroscopy and mass spectrometry (HPLC-NMR-MS), to the characterisation of ibuprofen metabolites from human urine

Summary The use of HPLC-NMR-MS for the detection and identification of the metabolites of ibuprofen present in a solid phase extract of human urine is described. Gradient reversed-phase HPLC was used to separate the components present in the extract, which were then characterised by a combination of stopped-flow¹H NMR and on line electrospray-MS. This approach led to the rapid identification of the known phase 1 human metabolites of ibuprofen, including hydroxy- and carboxy- metabolites, together with their respective glucuronide conjugates. In addition a probable artefact resulting from the dehydration of one of the side chainhydroxylated glucuronides was also identified.     

Non-target screening of organic contaminants in marine salts by gas chromatography coupled to high-resolution time-of-flight mass spectrometry

Gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF MS) has been applied to characterize the organic pollution pattern of marine salt samples collected in saltworks from the Spanish Mediterranean coast. After dissolving the samples in water, a solid-phase extraction was applied reaching with a 250-preconcentration factor. The screening methodology allowed the detection of sample components without any kind of pre-selection of target pollutants. The identity of components detected was established by accurate mass measurements and comparison of experimental full-acquisition spectra with theoretical MS libraries. Several organic pollutants were identified in the samples, like plasticizers - potentially toxic to humans - and fragrances -included within the group of pharmaceuticals and personal care products-, among others. Our results indicate that these contaminants can be found in the marine salt after the crystallization process. GC-TOF MS is a powerful technique for wide-scope screening of (semi)volatile, low-polar organic contaminants, able to investigate the presence of a large number of compounds. Searching of contaminants is not restricted to a target list of compounds. Therefore, unexpected contaminants can be discovered in an efficient way, with better sensitivity and selectivity than other conventional analytical techniques, and making use of the powerful qualitative information provided by full-spectrum acquisition at accurate mass.     

Two-dimensional liquid chromatography/mass spectrometry/mass spectrometry separation of water-soluble metabolites

Off-line two-dimensional liquid chromatography with tandem mass spectrometry detection (2D-LC/MS-MS) was used to separate a set of metabolomic species. Water-soluble metabolites were extracted from Escherichia coli and Saccharomyces cerevisae cultures and were immediately analyzed using strong cation exchange (SCX)-hydrophilic interaction chromatography (HILIC). Metabolite mixtures are well-suited for multidimensional chromatography as the range of components varies widely with respect to polarity and chemical makeup. Some currently used methods employ two different separations for the detection of positively and negatively ionized metabolites by mass spectrometry. Here we developed a single set of chromatographic conditions for both ionization modes and were able to detect a total of 141 extracted metabolite species, with an overall peak capacity of ca. 2500. We show that a single two-dimensional separation method is sufficient and practical when a pair or more of unidimensional separations are used in metabolomics.     

Process scale high performance liquid chromatography part IV—Examples of reversed phase separations

Summary The flexibility of process scale high performance liquid chromatography is demonstrated by three examples of reversed-phase separations (a) a standard purification (b) isolation of trace compounds, and (c) recovery from crystallisation mother liquors. It was shown that a material, thought to be acceptably pure, contained a toxic impurity, and a remaining impurity, a previously unseen component of potential therapeutic interest. Favourable cost data were indicated for example (3). This work was conducted in the Chemical Technology Unit, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M6O 1OD, UK.     

Optimization of the separation of polymethoxylated flavones in reversed phase liquid chromatography

Summary An optimization procedure for the chromatographic separation of polymethoxylated flavones is described. A polyhedron working volume is drawn from a truncated tetrahedron constructed from the four solvents selected. The response function is an n'th degree polynomial the coefficients of which are calculated through the least squares method by means of B=(XX)^–1XY in which XX is the information matrix (XX)^–1 the variance covariance matrix. X is the matrix of the model (polynomial built from the selected experiments) and X the transposed matrix. Y is the quality of the chromatogram defined by the resolution of each pair of solutes. An exchange algorithm matrix yields the minimum number of runs necessary to obtain a correct B. Isoresponses curves are drawn by intersection of a cubic volume which includes the polyhedron to give a better insight. An optimal zone is then determined and provides the solvent composition. An optimized chromatogram of 8 methoxylated flavones demonstrates the application of the method.     

Hydrocarbon group-type analysis with microcapillary-column liquid chromatography/conventional infrared spectrometry

Summary Slurry-packed microcapillary column liquid chromatography with conventional infrared detection is described for the group-type analysis of gasolines. The results indicate that the three eluted groups, saturates, olefins and aromatics, from the microcapillary column are easily detected by conventional microcomputerized infrared spectrometer coupled with a Teflon flow-cell with a good signal-to-noise ratio. This study shows the feasibility of microcapillary column liquid chromatography combined with a low-cost, conventional infrared spectrometer as a routine tool which allows the analyst to use an LC-IR system effectively and economically.     

High performance liquid chromatography coupled to nuclear magnetic resonance spectroscopy and mass spectrometry applied to plant products: Identification of ecdysteroids fromSilene otites

Summary HPLC coupled in parallel to nuclear magnetic resonance (NMR) and mass spectrometry (MS) has been used to obtain¹H NMR and mass spectra of a number of ecdysteroids present in an extract of the plantSilene otites. Reversed phase gradient chromatography was performed using a D₂0-acetonitrile-based solvent system. NMR and mass spectra were obtained for integristerone A, 20-hydroxyecdysone, 2-deoxy-20-hydroxyecdysone and 2-deoxyecdysone to provide structural confirmation using continuous and stopped flow HPLC-NMR. The combined HPLC-NMR-MS system described here provided a more comprehensive analysis of the ecdysteroids present in the extract than HPLC-NMR alone.     

Influence of solvent effects on retention for a porous polymer sorbent in reversed phase liquid chromatography

Summary The influence of acetonitrile, methanol and isopropanol as retention selectivily modifiers in reversed phase liquid chromatography on a poly(styrene-divinylbenzene) macroporous polymer sorbent (PLRP-S) is evaluated using the solvation parameter model. Retention results from a combination of adsorption and partitioning and is influenced by the equilibrium absorption of organic solvent by the polymer from the mobile phase. The sorption of solutes is dominated by the ease of cavity formation in or on the solvated sorbent, with a small contribution from lone pair-lone pair electron interactions. All polar interactions, such as dipole-type and hydrogenbond formation, are more favorable in the mobile phase and reduce retention. Changes in the uptake of organic solvent from the mobile phase affect kinetic properties of the column such as band broadening and porosity as well as retention. The PLRP-S solvated sorbent is suitable for solid-phase extraction and is more retentive than typical silica-based, bonded phase sorbents for extraction from water. As a surrogate system for estimating solute lipophilicity and biological activity through retention-property correlations it provides a poor fit for hydrogen-bond acid solutes and is too dipolar/polarizable to fit some models.     

Thiophenepropyltrichlorosilane as chemical modifier on silicagel for reversed phase chromatography

Summary Modification of silica gel with thiophene-propyl-trichlorosilane is described as well as the synthesis of the silane. The chromatographic performance and selectivity are demonstrated with various polyaromatic compounds. Thiophene-modified silica gel was found to exhibit a selectivity comparable with both ODS-and amino-phases.