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Analytical and Bioanalytical Chemistry (v.378, #8)

Molecular imprinting technology: a simple way of synthesizing biomimetic polymeric receptors by Antonio Martin-Esteban (pp. 1875-1875).

Molecularly imprinted polymers: towards highly selective stationary phases in liquid chromatography and capillary electrophoresis by E. Turiel; A. Martin-Esteban (pp. 1876-1886).

Molecularly imprinted polymers (MIPs) are synthetic polymers with a predetermined selectivity for a given analyte, or group of structurally related compounds, that make them ideal materials to be used in separation processes. In this sense, it is not surprising that the first applications of MIPs were as tailor-made chiral stationary phases in liquid chromatography. However, peak broadening and tailing, especially of the more retained enantiomers, were observed. Accordingly, this paper gives an overview of the attempts carried out during the recent years to improve the chromatographic performance of MIPs in liquid chromatography and capillary electrophoresis as well as the more recent applications. We conclude that MIPs are very promising materials to be used as selective stationary phases in chromatography although further developments are necessary in order to fully exploit their potential.

Keywords: Imprinted polymers; Liquid chromatography; Capillary electrophoresis

Molecularly imprinted polymers as antibody and receptor mimics for assays, sensors and drug discovery by Lei Ye; Karsten Haupt (pp. 1887-1897).

Biological receptors play an important role in affinity-based drug assays, biosensors, and at different stages during the modern drug discovery process. The molecular imprinting technology that has recently emerged has shown great potential for producing biomimetic receptors that challenge their natural counterparts. In this paper, we will overview recent progress in the use of molecularly imprinted polymers for drug assays, assembly of biomimetic sensors, and screening of combinatorial libraries. In addition, examples of using artificially-created binding sites to control synthetic reactions will be discussed. The “screening-of-building blocks” approach is expected to accelerate generation of valuable lead compounds, without the costly synthesis of large chemical libraries.

Keywords: Molecularly imprinted polymer; Immunoassay; Biosensor; Library screening; Drug discovery

Synthetic polymers adsorbing bisphenol A and its analogues prepared by covalent molecular imprinting using bisphenol A dimethacrylate as a template molecule by Takashi Ikegami; Woo-Sang Lee; Hiroyuki Nariai; Toshifumi Takeuchi (pp. 1898-1902).

Synthetic polymers which can adsorb bisphenol A (BPA) and related compounds were prepared by a covalent molecular imprinting technique. BPA dimethacrylate, used as template molecule, was polymerized with a crosslinker, triethylene glycol dimethacrylate (TEGDMA) or trimethylol propane trimethacrylate (TRIM). After the polymerization treatment with dilute NaOH was used to cleave BPA from the polymers. For high recovery of BPA with low polymer matrix degradation, the hydrolysis conditions were determined to be treatment with 1.0 mol L⁻¹ NaOH for 48 h. The binding sites generated by the hydrolysis were evaluated by determination of the retentivity of BPA, BPA analogues, and other endocrine disruptors. The polymers strongly adsorbed compounds with two hydroxyl groups at the 4,4′-positions. Generally the TEGDMA-based polymers had stronger affinity than the TRIM-based polymers, although the TRIM-based polymer adsorbed steroidal hormones with two hydroxyl groups, for example 17α-estradiol and 17β-estradiol, more strongly than the TEGDMA-based polymer, meaning that the crosslinkers affected the properties of the binding sites and, depending upon the target molecules, suitable crosslinkers should be chosen in this system.

Keywords: Covalent molecular imprinting; Bisphenol A dimethacrylate; Bisphenol A; Endocrine disruptors; Hydrogen bonding

Analysis of wheat extracts for ochratoxin A by molecularly imprinted solid-phase extraction and pulsed elution by Simon N. Zhou; Edward P. C. Lai; J. David Miller (pp. 1903-1906).

A molecularly imprinted solid-phase extraction (MISPE) method has been developed for the rapid analysis of wheat extracts for ochratoxin A (OTA). Molecularly imprinted polymer (MIP) particles were synthesized from N-phenylacrylamide (PAM) and slurry-packed into a micro-column for selective solid-phase extraction (SPE) of OTA. With water flowing at 0.5 mL min⁻¹, a total binding capacity of 30 ng OTA was determined for the 20 mg of MIP particles. MISPE conditions were optimized using OTA in methanol/acetic acid (99:1 v/v). Nearly 100% binding could be achieved from one 20-μL injection of sample containing up to 30 ng of OTA. Pulsed elution (PE) using methanol/triethylamine (99:1 v/v) was good for the quantitative desorption of OTA. The MISPE–PE method, with fluorescence detection at λ _ex=385 nm and λ _em=445 nm, afforded a detection limit of 5.0 ng mL⁻¹ (or 0.1 ng in 20 μL of sample injected) for OTA. Recovery of OTA from wheat extracts was 103±3%. Each MISPE–PE analysis required less than 5 min to complete.

Keywords: Ochratoxin A; Molecularly imprinted polymer; Solid-phase extraction; Pulsed elution; Wheat extracts; Rapid screening

Chiral resolution of derivatized amino acids using uniformly sized molecularly imprinted polymers in hydro-organic mobile phases by Jun Haginaka; Chino Kagawa (pp. 1907-1912).

Uniformly sized molecularly imprinted polymers (MIPs) for Boc-l-Trp were prepared using ethylene glycol dimethacrylate (EDMA) as the cross-linker, and methacylic acid (MAA) and/or 4-vinylpyridine (4-VPY) as the functional monomers or without use of a functional monomer. The MIPs prepared were evaluated using acetonitrile or a mixture of phosphate buffer and acetonitrile as the mobile phase. The Boc-l-Trp-imprinted EDMA polymers can recognize Boc-l-Trp by its molecular shape, and can thus afford the enantioseparation of Boc-Trp. Besides the molecular shape recognition, the hydrophobic interactions with the polymer backbones as well as the hydrogen-bonding interactions of Boc-l-Trp with carboxyl and pyridyl groups in the polymers should work for the retention and recognition of Boc-l-Trp on the imprinted MAA-co-EDMA and 4-VPY-co-EDMA polymers, respectively, in the hydro-organic mobile phase. The hydrogen-bonding interactions seem to become dominant when only acetonitrile is used as the mobile phase. The Boc-l-Trp-imprinted 4-VPY-co-EDMA polymers gave the highest retentivity and enantioselectivity for Boc-Trp among the MIPs prepared. However, the simultaneous use of MAA and 4-VPY was not effective for the enantioseparation of Boc-Trp in a hydro-organic mobile phase. Furthermore, the baseline separation of Boc-Trp enantiomers was attained within 10 min on the Boc-l-Trp-imprinted 4-VPY-co-EDMA polymers under the optimized HPLC conditions.

Keywords: Molecular Imprinting; Molecularly imprinted polymer; Chiral stationary phase; Enantiomer separation; Derivatized amino acid

Peptide recognition via hierarchical imprinting by Maria Magdalena Titirici; Börje Sellergren (pp. 1913-1921).

Silica particles containing immobilised peptidic templates have been used for the generation of hierarchically imprinted polymers. The pores of the silica mould were filled with a mixture of monomers/initiator and polymerised, followed by dissolution of the silica template. This method leaves behind imprinted polymers with binding sites located at the surface, which are capable of recognising larger molecules with the same immobilised epitope. All the products resulting from solid-phase synthesis of peptides were characterised by elemental analysis, FT-IR spectroscopy and fluorescence microscopy. The hierarchically imprinted polymers generated from these products were characterised by elemental analysis, FT-IR spectroscopy, fluorescence microscopy, scanning electron microscopy (SEM) and nitrogen adsorption, providing evidence concerning the reproducibility of each step. The chromatographic properties of the materials have been investigated and the advantages of the immobilisation method have been proven. The materials exhibit selectivity for their templates and other structurally related dipeptides. Furthermore, the polymers proved to be capable of recognising larger peptides containing the immobilised sequence.

Keywords: Molecularly imprinted polymer; Hierarchical imprinting; Peptide detection; Solid-phase synthesis; Liquid chromatography

Electrochemical sensing with electrodes modified with molecularly imprinted polymer films by M. C. Blanco-López; S. Gutiérrez-Fernández; M. J. Lobo-Castañón; A. J. Miranda-Ordieres; P. Tuñón-Blanco (pp. 1922-1928).

membranes electropolymerised at the electrode surface;casting of polymeric membranes by drop-coating a solution of pre-formed polymer (polyphosphazene) and template in a low-boiling-point solvent on to the electrode surface;preparation of composite membranes containing conductive material (graphite or carbon black), acrylic-type molecularly imprinted polymers (small particle size), and PVC as binder; andin-situ polymerisation of a thin layer of acrylic imprinted polymer deposited on the electrode surface by spin coating. All the options evaluated offer the possibility of controlling electrode characteristics such as hydrophobic/hydrophilic character, permeability, or film thickness, which are essential for obtaining good sensor performance.

Keywords: Molecularly imprinted polymers; Voltammetric sensors; Biomimetics

Bioimprinted QCM sensors for virus detection—screening of plant sap by Franz L. Dickert; Oliver Hayden; Roland Bindeus; Karl-J. Mann; Dieter Blaas; Elisabeth Waigmann (pp. 1929-1934).

Surface imprinting techniques on polymer-coated quartz-crystal microbalances (QCM) have been used to detect tobacco mosaic viruses (TMV) in aqueous media. Molecularly imprinted polymers (MIP), tailor-made by self organisation of monomers around a template (TMV), were generated directly on the gold electrodes. Imprinted trenches on the polymer surface mimicking the shape and surface functionality of the virus serve as recognition sites for re-adsorption after washing out of the template. The sensors are applicable to TMV detection ranging from 100 ng mL⁻¹ to 1 mg mL⁻¹ within minutes. Furthermore, direct measurements without time-consuming sample preparation are possible in complex matrices such as tobacco plant sap.

Keywords: Tobacco mosaic virus; Quartz-crystal microbalance; Molecular imprinting; Atomic force microscopy (AFM)

Multidimensional separations in analytical chemistry by Marja-Liisa Riekkola (pp. 1935-1935).

Perspectives of on-line coupled liquid chromatography–gas chromatography by Tuulia Hyötyläinen; Marja-Liisa Riekkola (pp. 1936-1938).

Comprehensive two-dimensional gas chromatography—a powerful and widely applicable technique by Jan Beens; Udo A. Th. Brinkman (pp. 1939-1943).

On-line LC-GC and comprehensive two-dimensional LCxGC-ToF MS for the analysis of complex samples by Hans-Gerd Janssen; Sjaak de Koning; Udo A. Th. Brinkman (pp. 1944-1947).

Trends in chemometric analysis of comprehensive two-dimensional separations by Amanda E. Sinha; Bryan J. Prazen; Robert E. Synovec (pp. 1948-1951).

Multidimensional LC-LC and LC-CE for high-resolution separations of biological molecules by Charles R. Evans; James W. Jorgenson (pp. 1952-1961).

In multidimensional separations, two or more independent separation methods are coupled in an effort to resolve complex mixtures. The displacement mechanisms of each method should be orthogonal, such that little correlation exists between the retention of compounds in each dimension. When multiple orthogonal separation methods are coupled such that all sample components are subjected to complete analysis on all dimensions, the method is considered “comprehensive”. The primary advantage of comprehensive multidimensional separations over their one-dimensional counterparts is the potential for dramatically enhanced resolution. High resolving power can be achieved because the peak capacity of a comprehensive multidimensional separation is roughly equal to the product of the individual peak capacities of each dimension. In this review, the theory and instrumentation of two-dimensional liquid chromatography (LC-LC) and liquid chromatography-capillary electrophoresis (LC-CE) separations are discussed. Some applications of these techniques to the separation of biological molecules are highlighted. Future directions for the development of multidimensional separations are also considered.

Keywords: Multidimensional separations; Liquid chromatography; Capillary electrophoresis; LC-LC; LC-CE; Biomolecules

Approaches for on-line coupling of extraction and chromatography by Tuulia Hyötyläinen; Marja-Liisa Riekkola (pp. 1962-1981).

This review provides an overview of the approaches available in order to perform on-line coupling of various extraction techniques with liquid and gas chromatography, for the analysis of semivolatile and nonvolatile analytes in liquid and solid samples. The main focus is on the instrumental set-up of these techniques. Selected real applications are described by way of illustration. The extraction methods suitable for on-line coupling covered in this review are: liquid-liquid extraction, solid-phase extraction, membrane-based techniques, pressurised liquid extraction, supercritical fluid extraction, and microwave- and sonication-assisted extractions. The following systems are not covered in this review: on-line coupled solid-phase extraction-liquid chromatography, purge-and-trap-GC, and membrane extraction with a sorbent interface-GC.

Keywords: On-line coupling; Liquid chromatography; Gas chromatography; Extraction; Solid and liquid samples

Characterisation of organic compounds in aerosol particles from a Finnish forest by on-line coupled supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry by Masahiko Shimmo; Jaana Jäntti; Pasi Aalto; Kari Hartonen; Tuulia Hyötyläinen; Markku Kulmala; Marja-Liisa Riekkola (pp. 1982-1990).

During the European Union project Quantification of Aerosol Nucleation in the European Boundary Layer (QUEST), which began in spring 2003, atmospheric aerosol particles were collected in a Finnish Scots pine forest using a high-volume sampler. The organic compounds in the filter samples were then analysed by on-line coupled supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry (SFE–LC–GC–MS). The sample was first extracted by SFE. During LC the extracts were fractionated into three fractions according to polarity. The final separation was carried out by GC–MS. A fraction volume as high as 840 μL was transferred to the GC, using the partial concurrent eluent evaporation technique. The same instrumentation, with an in-situ SFE derivatisation method, was used to analyse organic acids. Major compounds such as n-alkanes and PAH were analysed quantitatively. Their concentrations were lower than those usually observed in urban areas or in other forest areas in Europe. The wind direction was one of the most important factors affecting changes in the daily concentrations of these compounds. Scots pine needles were analysed with the same system to obtain reference data for identification of biogenic compounds in aerosol particles. Other organic compounds found in this study included hopanes, steranes, n-alkanals, n-alkan-2-ones, oxy-PAH, and alkyl-PAH; some biogenic products, including oxidation products of monoterpenes, were also identified.

Keywords: On-line coupling; Supercritical fluid extraction; Liquid chromatography–gas chromatography; Aerosol particles; Organic compounds; Scots pine forest

On-line coupling of microporous membrane liquid–liquid extraction and gas chromatography in the analysis of organic pollutants in water by Kati Lüthje (née Kuosmanen); Tuulia Hyötyläinen; Marja-Liisa Riekkola (pp. 1991-1998).

A method for the determination of hydrophobic pollutants in surface waters was developed. The pretreatment was done with microporous membrane liquid–liquid extraction, the extract was eluted to a sample loop in the large-volume injector valve of the gas chromatograph and the extract was injected on-line to the gas chromatograph. The method was optimised using standard compounds and the linearity, the limits of detection and quantification of the method were studied. The method allowed the determination of hydrophobic pesticides and PAHs at the ng L⁻¹ level. The RSD values for the repeatability of the method varied from 4.2% to 25.6%, being on average 9.5%. Surface water samples from Finnish lakes and rivers were analysed.

Keywords: Microporous membrane liquid–liquid extraction; Large-volume injection; On-line coupling; Pesticides; Polycyclic aromatic hydrocarbons (PAHs)

Separation of fatty acid methyl esters by comprehensive two-dimensional supercritical fluid chromatography with packed columns and programming of sampling duration by Yukio Hirata; Ito Sogabe (pp. 1999-2003).

Fatty acid methyl esters from various fats and oils were separated by comprehensive two-dimensional supercritical fluid chromatography with conventional packed columns and FID detection. The first dimension was a silica gel column and the second dimension was an ODS column. This combination was largely orthogonal for the separation of fatty acid methyl esters. The first dimension separations were primarily based on the number of double bonds while the second dimension separations were based on the chain length. The highly-ordered chromatograms and improved resolution allowed the easy detection and identification of minor components. Although the first dimension separations were performed under isobaric conditions where the peak width increased in proportion to the retention, the programming of the sampling duration allowed us to maintain the optimum re-injection frequency (3–4 times) per peak into the second dimension and so to minimize the total analysis time without deteriorating the resolution.

Keywords: Supercritical fluid chromatography; Packed column; Comprehensive two-dimensional chromatography; Fatty acid methyl ester

A toxic reagent-free method for normal-phase matrix solid-phase dispersion extraction and reversed-phase liquid chromatographic determination of aldrin, dieldrin, and DDTs in animal fats by N. Furusawa (pp. 2004-2007).

A method for the determination of aldrin, dieldrin, DDT, DDE, and DDD contamination in animal fats (beef tallow, lard, and chicken fat) without using toxic reagents is developed, that uses high-performance liquid chromatography after the sample has been prepared by matrix solid-phase dispersion (MSPD) with acidic alumina oxide. A reversed-phase C₁-silica column with a mobile phase of 50% (v/v) ethanol solution (in water) and a photo-diode array detector were used for the determination. Average recoveries of the target compounds (0.2–5.0 μg g⁻¹) ranged from 84–98%, with coefficients of variation of <5%. The limits of quantitation were ≤0.16 μg g⁻¹for AD, ≤0.10 μg g⁻¹ for DD, ≤0.06 μg g⁻¹ for DDT, ≤0.07 μg g⁻¹ for DDE, and ≤0.05 μg g⁻¹for DDD. No toxic reagents were used at all.

Keywords: DDT; Aldrin; Dieldrin; HPLC; Matrix solid-phase dispersion

Toxicological classification of urine samples using pattern recognition techniques and capillary electrophoresis by Simeone Zomer; Christelle Guillo; Richard G Brereton; Melissa Hanna-Brown (pp. 2008-2020).

In toxicology, hazardous substances detected in organisms may often lead to different pathological conditions depending on the type of exposure and level of dosage; hence, further analysis on this can suggest the best cure. Urine profiling may serve the purpose because samples typically contain hundreds of compounds representing an effective metabolic fingerprint. This paper proposes a pattern recognition procedure for determining the type of cadmium dosage, acute or chronic, administrated to laboratory rats, where urinary profiles are detected using capillary electrophoresis. The procedure is based on the composition of a sample data matrix consisting of areas of common peaks, with appropriate pre-processing aimed at reducing the lack of reproducibility and enhancing the potential contribution of low-level metabolites in discrimination. The matrix is then used for pattern recognition including principal components analysis, cluster analysis, discriminant analysis and support vector machines. Attention is particularly focussed on the last of these techniques, because of its novelty and some attractive features such as its suitability to work with datasets that are small and/or have low samples/variable ratios. The type of cadmium administration is detected as a relevant feature that contributes to the structure of the sample matrix, and samples are classified according to the class membership, with discriminant analysis and support vector machines performing complementarily on a training and on a test set.

Keywords: Pattern recognition; Capillary electrophoresis; Toxicology; Support vector machines

Bioguided extraction of polyphenols from grape marc by using an alternative supercritical-fluid extraction method based on a liquid solvent trap by B. Palenzuela; L. Arce; A. Macho; E. Muñoz; A. Ríos; M. Valcárcel (pp. 2021-2027).

The biological activity of polyphenols extracted from grape marc was studied with a view to finding a new use for this winery waste. Polyphenols were extracted by using an alternative supercritical-fluid extraction method based on the use of a liquid trap that allows extracted polyphenols to be retained in a saline buffer, thus avoiding the need for the organic solvent required to elute polyphenols from a solid trap. The major extraction variables influencing the performance of the liquid trap (viz. CO₂ modifier content, flow-rate, extraction time and trap volume) were optimized. The proposed method was applied to the supercritical-fluid extraction extraction of 0.3 g grape marc with CO₂ modified with 3% methanol at 350 bar at 50 °C (CO₂ density 0.9 g mL^-1) for 20 min, using a liquid flow-rate of 0.9 mL min^-1. The polyphenol extracts thus obtained exhibited cytotoxic effects that induced apoptosis in tumour cells.

Keywords: Supercritical-fluid extraction; Liquid trap; Apoptosis; Cell cycle; Polyphenols

Flow injection analysis of gallic acid with inhibited electrochemiluminescence detection by Xiang-Qin Lin; Feng Li; Yong-Qiang Pang; Hua Cui (pp. 2028-2033).

A flow injection (FI)–electrochemiluminescent (ECL) method has been developed for the determination of gallic acid, based on an inhibition effect on the Ru(bpy)₃ ²⁺/tri-n-propylamine (TPrA) ECL system in pH 8.0 phosphate buffer solution. The method is simple and convenient with a determination limit of 9.0×10⁻⁹ mol/L and a dynamic concentration range of 2×10⁻⁸–2×10⁻⁵ mol/L. The relative standard deviation (RSD) was 1.0% for 1.0×10⁻⁶ mol/L gallic acid (n=11). It was successfully applied to the determination of gallic acid in Chinese proprietary medicine—Jianming Yanhou Pian. The inhibition mechanism proposed for the quenching effect of the gallic acid on the Ru(bpy)₃ ²⁺/TPrA ECL system was the interaction of electrogenerated Ru(bpy)₃ ^2+* and o-benzoquinone derivative at the electrode surface. The ECL emission spectra and UV-visible absorption spectra were applied to confirm the mechanism.

Keywords: Electrochemiluminescence; Flow injection; Determination; Gallic acid; Ru(bpy)₃ ²⁺ ; Tri-n-propylamine

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Analytical and Bioanalytical Chemistry (v.378, #8)