Preparation and evaluation of a new synthetic polymeric chiral stationary phase for HPLC based on the trans-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid bis-4-vinylphenylamide monomer

A new synthetic polymeric chiral stationary phase for liquid chromatography was prepared via free-radical-initiated polymerization of trans-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid bis-4-vinylphenylamide. The new polymeric chiral stationary phase (CSP) showed enantioselectivity for many chiral compounds in multiple mobile phases. High stability and sample capacities were observed on this polymeric chiral stationary phase. Mobile phase components and additives affected chiral separation greatly. This new synthetic chiral stationary phase is complementary to two other related commercially available CSPs: the P-CAP and P-CAP-DP columns. Interactions between the chiral stationary phase and analytes that lead to retention and chiral recognition include hydrogen bonding, dipolar, and π–π interactions. Repulsive (steric) interactions also contribute to chiral recognition. Figure LC chromatograms showing the analytical (blue) and preparative (red) separations of N-(3,5-dinitrobenzoylleucine) enantiomers on a new synthetic polymeric chiral stationary phase     

Dicationic ionic liquid stationary phase for GC-MS analysis of volatile compounds in herbal plants

The seeming “dual nature” of ionic liquids (ILs) for separating both apolar and polar compounds suggests that ILs may have a great potential for complex samples like essential oils from herbal plants that contain a great variety of compounds. In the present work, a geminal dicationic IL, 1,9-di(3-vinylimidazolium)nonane bis[(trifluoromethyl)sulfonyl]imidate, was investigated for this purpose. To find the best way to achieve satisfactory separations simultaneously for the compounds in essential oils, the dicationic IL was used as the stationary phase for capillary gas chromatography (GC) in two ways, either in its pure state or as a mixed stationary phase with monocationic ILs and a polysiloxane diluent. Interestingly, it was found that the mixed stationary phase exhibited a much better selectivity for polar and nonpolar compounds than either the dicationic IL or the polysiloxane, suggesting that a kind of synergistic effect occurred when these stationary phases were combined in the way described. A comparison with two commercial stationary phases (polar and nonpolar) indicated that this novel mixed stationary phase behaved in a way closer to a polar stationary phase in terms of selectivity and elution order. The present work demonstrates that the mixed stationary phase is efficient and selective and can be an alternative choice for the GC analysis of samples of complex composition. Figure Divinyldiimidazolium-based ionic liquid stationary phase     

Preparation and enantioseparation characteristics of three chiral stationary phases based on modified β-cyclodextrin for liquid chromatography

In order to study the effect of the nature and the length of the spacer, three mixed 10-undecenoate/phenylcarbamate derivatives of β-cyclodextrin have been prepared and linked to allylsilica gel by means of a radical reaction. The chiral recognition ability of the resulting materials, when used as liquid chromatography chiral stationary phases (CSPs), was evaluated using heptane and either 2-propanol or chloroform as organic mobile-phase modifiers. A large variety of racemic compounds have been separated successfully on these CSPs (mainly pharmaceuticals and herbicides). Optimization of these separations was discussed in terms of mobile-phase composition and structural patterns of the injected analytes. The efficiencies of the three prepared materials were compared to those of previously described perphenylated-β-cyclodextrin column and to analogous cellulose derivative-based CSPs. Schematic illustration of the b-cyclodextrin/mandelic acid inclusion complex     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Studies on the analytical performance of a non-covalent coating with N,N-didodecyl-N,N-dimethylammonium bromide for separation of basic proteins by capillary electrophoresis in acidic buffers in 25-and 50-μm capillaries

Capillaries (25-and 50-μm inner diameter) coated with a double-alkyl-chain cationic surfactant N,N-didodecyl-N,N-dimethylammonium bromide (DDAB) were used for the separation of four basic standard proteins in buffers of pH 4 at various ionic strengths. The choice of buffer is critical for the analytical performance. Ammonium ions must be avoided in the buffer used in the non-covalent coating procedure owing to competition with the surfactant. Phosphate buffer gave a better separation performance than some volatile buffers; the reason seems to be a complex formation between the proteins and dihydrogenphosphate ions, which decreases tendencies for adsorption to the capillary surface. The DDAB coating was easy to produce and stable enough to permit, without recoating, consecutive separations of the proteins for up to 100 min with good precision in migration times and peak areas. A strong electroosmotic flow gives rapid separations, which is of special importance when commercial instruments are used, since the choice of the length of the capillary is restricted. Figure EOF stability in 25 micrometer i.d. capillaries. Consecutive injections of mesityloxide performed after an initial coating with 1.0     

Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones

The derivatization of cysteine-containing peptides with benzoquinone compounds is rapid, quantitative and specific in acidic media. The conversion of cysteines into hydrophobic benzoquinone-adducted residues in peptides is used here to alter the chromatographic properties of cysteinyl peptides during liquid chromatography separation. The benzoquinone derivatization is shown to allow the accurate selection of cysteine-containing peptides of bovine serum albumin tryptic digest by diagonal reversed-phase chromatography, which consists of one primary and a series of secondary identical liquid chromatographic separations, before and after a cysteinyl-targeted modification of the peptides by benzoquinone compounds. Figure Diagonal chromatographic selection of cysteinyl peptides modified with benzoquinones Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Outer-membrane proteomic maps and surface-exposed proteins of <Emphasis Type="Italic">Legionella pneumophila</Emphasis> using cellular fractionation and fluorescent labelling

Bacterial surface-associated proteins play crucial roles in host–pathogen interactions and pathogenesis. The identification of these proteins represents an important goal of bacterial proteomics for vaccine development, but also for environmental concerns such as microbial biosensing. Here, we developed such an approach for Legionella pneumophila, a bacterium that causes severe pneumonia. We propose a complementary strategy consisting of (1) a fluorescent labelling of surface-exposed proteins in parallel with (2) a fractionation of the outer-membrane protein extract. These two distinct protein populations were subsequently separated using two-dimensional gel electrophoresis and characterised by mass spectrometry. Within these populations, we found proteins which were expected for the compartments studied, but also a great number of proteins never experimentally described, and also a non-negligible fraction of proteins never described in these fractions. These data provided new routes of inspection for transport and host recognition for Legionella pneumophila. In addition, these results on the membranome and surfaceome show that Legionella in the stationary phase of growth possesses the major determinants to infect host cells. Figure Electron micrograph of Legionella pneumophila in stationnary phase of growth Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Presented at the Annual French National Symposium on Mass Spectrometry, Electrophoresis and Proteomics, 20–23 September 2007 in Pau, France     

Profiling of 3,4-methylenedioxymethamphetamine by means of high-performance liquid chromatography

An impurity-profiling method for 3,4-methylenedioxymethamphetamine (MDMA) is presented. The impurities of interest were extracted by solid-phase extraction (SPE) on Bakerbond C₁₈ spe columns from a weakly alkaline solution (pH 8.5). Development of the extraction conditions covered selection of the buffer for dissolution of the sample and the volume of the eluent used to elute the impurities. An important part of the studies was to optimise the separation conditions, and the simplex method was used for this purpose. Cluster analysis was applied for comparison of samples and its grouping. The developed method was based on the areas of 33 selected peaks corresponding to MDMA impurities. All examined samples were correctly classified into clusters corresponding to the synthetic route.      

Rapid response behavior,at room temperature,of a nanofiber-structured TiO<Subscript>2</Subscript> sensor to selected simulant chemical-warfare agents

A chemical prototype sensor was constructed based on nanofiber-structured TiO₂ and highly sensitive quartz resonators. The gas-sensing behavior of this new sensor to selected simulant warfare agents was investigated at room temperature. Results showed rapid response and good reversibility of this sensor when used with high-purity nitrogen. This provides a simple approach to preparation of materials needed as chemical sensors for selected organic volatiles or warfare agents. Figure Sensing behavior of TiO₂ nanofiber sensor to chemical vapors     

Recent advances in capillary electrophoretic analysis of individual cells

Because variability exists within populations of cells, single-cell analysis has become increasingly important for probing complex cellular environments. Capillary electrophoresis (CE) is an excellent technique for identifying and quantifying the contents of single cells owing to its small volume requirements and fast, efficient separations with highly sensitive detection. Recent progress in both whole-cell and subcellular sampling has allowed researchers to study cellular function in the areas of neuroscience, oncology, enzymology, immunology, and gene expression.      

Aptamers as molecular recognition elements for electrical nanobiosensors

Recent advances in nanotechnology have enabled the development of nanoscale sensors that outperform conventional biosensors. This review summarizes the nanoscale biosensors that use aptamers as molecular recognition elements. The advantages of aptamers over antibodies as sensors are highlighted. These advantages are especially apparent with electrical sensors such as electrochemical sensors or those using field-effect transistors. Figure Feeling proteins with aptamer-functionalized carbon nanotubes     

Multivariate classification and modeling in surface water pollution estimation

The present study deals with the application of self-organizing maps (SOM) and multiway principal-components analysis to classify, model, and interpret a large monitoring data set for surface water quality. The chemometric methods applied made it possible to reveal specific quality patterns of the chemical and biological parameters used to monitor the water quality (relation between water temperature, turbidity, hardness, colibacteria), seasonal impacts during the long period of observation and the relative independence on the spatial location of the sampling sites (water supply sources for the City of Trieste). Figure The schematic procedure for surface water pollution estimation supported by neural network-based classification and multivariate factor analysis     

Pitfalls in compound-specific isotope analysis of environmental samples

In the last decade compound-specific stable isotope analysis (CSIA) has evolved as a valuable technique in the field of environmental science, especially in contaminated site assessment. Instrumentation and methods exist for highly precise measurements of the isotopic composition of organic contaminants even in a very low concentration range. Nevertheless, the determination of precise and accurate isotope data of environmental samples can be a challenge. Since CSIA is gaining more and more popularity in the assessment of in situ biodegradation of organic contaminants, an increasing number of authorities and environmental consulting offices are interested in the application of the method for contaminated site remediation. Because of this, it is important to demonstrate the problems and limitations associated with compound-specific isotope measurements of environmental samples. In this review, potential pitfalls of the analytical procedure are critically discussed and strategies to avoid possible sources of error are provided. In order to maintain the analytical quality and to ensure the basis for reliable stable isotope data, recommendations on groundwater sampling, and sample preservation and storage are given. Important aspects of sample preparation and preconcentration techniques to improve sensitivity are highlighted. Problems related to chromatographic resolution and matrix interference are discussed that have to be considered in order to achieve accurate gas chromatography/isotope ratio mass spectrometry measurements. As a result, the need for a thorough investigation of compound-specific isotope fractionation effects introduced by any step of the overall analytical method by standards with known isotopic composition is emphasized. Finally, we address some important points that have to be considered when interpreting data from field investigations. Figure CSIA Principal (Carbon)     

Determination of total <Emphasis Type="Italic">trans</Emphasis> fats and oils by infrared spectroscopy for regulatory compliance

The mandatory requirement in many countries to declare the amount of trans fat present in food products and dietary supplements has led to a need for sensitive and accurate methodologies for the rapid quantitation of total trans fats and oils. Capillary gas chromatography (GC) and infrared spectroscopy (IR) are the two methods most commonly used to identify and quantify trans fatty acids for food labeling purposes (see the article by Delmonte and Rader in this ABC issue for a detailed presentation of GC methodology). The present article provides a comprehensive review of the IR technique and the current attenuated total reflection (ATR) Fourier-transform (FT) IR methodologies for the rapid determination of total trans fats and oils. This review also addresses potential sources of interferences and inaccuracies in FTIR determinations, particularly those done at low trans levels. Recent observations have shown that the presence of saturated fats caused interferences in the FTIR spectra observed for trans triacylglycerols. The recognition and resolution of previously unresolved quantitative issues improved the accuracy and sensitivity of the FTIR methodology. Once validated, it is anticipated that the new negative second-derivative ATR-FTIR procedure will make IR spectroscopy more suitable than ever, and a rapid alternative and/or complementary method to GC, for the rapid determination of total trans fats for regulatory compliance. Figure Infrared light bouncing inside an internal reflection crystal     

Chromatographic characterization of molecularly imprinted polymers

Recent efforts in the investigation of chromatographic characterization of molecularly imprinted polymers (MIPs) have focused mainly on the nature of heterogeneous binding sites. More data on the thermodynamics than on the kinetic features of MIP columns have been published. The present article addresses the sources of peak broadening and tailing, which are the main drawbacks often associated with imprinted polymers in chromatography for practical applications. With use of the theory of nonlinear chromatography, the peak properties of a MIP column, including the retention and peak broadening and tailing, can be well interpreted. Efforts to improve chromatographic efficiency using MIPs prepared by approaches different from the conventional method, including covalent imprinting and the format of uniformly sized spherical microbeads, are reviewed and discussed. This review leads to the conclusion that nonlinear chromatography theory is useful for characterizing chromatographic features of MIP columns, since a MIP is essentially an affinity-based chromatographic stationary phase. We expect more theoretical and experimental studies on the kinetic aspects of MIP columns, especially the factors influencing the apparent rate constant, as well as the analysis of the influences of mobile-phase composition on the chromatographic performance. In addition to revealing the affinity interaction by molecular recognition, slow nonspecific interactions which may be inherited from the imperfect imprinting and may be involved in the rebinding of the template to MIPs also need to be characterized. Figure The peak broadening and tailing associated often with molecularly imprinted polymers (MIPs) in column chromatography for practical applications can be well characterized by the theory of nonlinear chromatography.     

Hydrophilic interaction liquid chromatography (HILIC) in proteomics

In proteomics, nanoflow multidimensional chromatography is now the gold standard for the separation of complex mixtures of peptides as generated by in-solution digestion of whole-cell lysates. Ideally, the different stationary phases used in multidimensional chromatography should provide orthogonal separation characteristics. For this reason, the combination of strong cation exchange chromatography (SCX) and reversed-phase (RP) chromatography is the most widely used combination for the separation of peptides. Here, we review the potential of hydrophilic interaction liquid chromatography (HILIC) as a separation tool in the multidimensional separation of peptides in proteomics applications. Recent work has revealed that HILIC may provide an excellent alternative to SCX, possessing several advantages in the area of separation power and targeted analysis of protein post-translational modifications. Figure Artistic impression of the HILIC separation mechanism     

Characterization of imazamox degradation by-products by using liquid chromatography mass spectrometry and high-resolution Fourier transform ion cyclotron resonance mass spectrometry

The photodecomposition of imazamox, a herbicide of the imidazolinone family, was investigated in pure water. The main photoproducts from the photolysis were followed over time by liquid chromatography mass spectrometry and structures were proposed from exact mass determinations obtained by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The method comprised exact mass determination with better than 0.2 ppm mass accuracy and a corresponding structural visualization taking care of respective isotopes with an adapted van Krevelen diagram that enabled a systematic approach to the characterisation of the elementary composition of each photoproduct. By taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, the derived 2D van Krevelen diagram (O/C; H/C; m/z) enabled one to structurally differentiate the formed photoproducts and to propose a degradation pathway for imazamox. Figure Overview of applied method to analyse the photolysis process of imazamox herbicide     

Analysis of glycans in glycoproteins by diffusion-ordered nuclear magnetic resonance spectroscopy

Enzymatically cleaved glycans from sub-milligram quantities of erythropoietin (EPO) and ovalbumin have been analyzed, without further purification, by two-dimensional diffusion-ordered nuclear magnetic resonance spectroscopy. At NMR sample concentrations below 50 μmol L⁻¹ the major components of the oligosaccharide fractions could be distinguished by their anomeric proton chemical shift and their size-dependent diffusion coefficients. Figure ¹H NMR diffusion decay curves of anomeric protons in the EPO glycan fraction     

Chiral ligand-exchange chromatography of amino acids using porous graphitic carbon coated with a dinaphthyl derivative of neamine

In this paper, we describe the preparation and the evaluation of a porous graphitic carbon (PGC) column coated with a new dinaphthyl derivative of neamine for chiral ligand-exchange (LE) chromatography. It was shown that the graphitic surface/dinaphthyl anchor system efficiently (1.15 μmol/m²) and stably (three months of intensive use) adsorbs the neamine template onto the chromatographic support. The resulting coated PGC stationary phase showed appreciable LE-based enantioselective properties towards several native amino acids. Chromatographic separation of methionine enantiomers using a dinaphtyl neamine-based ligand-exchange chiral stationary phase     

Simultaneous use of multiple fluorescent reporter dyes for glucose sensing in aqueous solution

The simultaneous use of several fluorescent reporter dyes in a multicomponent boronic acid-based glucose sensing system is reported. In one application, two dyes with widely different emission wavelengths are used to report changes in glucose concentration. A third glucose-insensitive dye was then added to act as a reference dye and provide for a ratiometric correction to the two reporter dye signals. The inclusion of such a reference dye reduces errors arising from sources such as fluctuations in lamp intensity and sample dilution. The simultaneous use of multiple fluorescent reporter dyes