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ABSTRACT: Detailed molecular analysis by Direct Analysis in Real Time High Resolution Mass Spectrometry (DART-HRMS) of ester and amide-terminated monolayers is demonstrated. The structural information obtained allowed monitoring of the progress of a 4-step surface modification.
Chemical Communications 12/2012; · 6.17 Impact Factor
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ABSTRACT: Cu-free "click" chemistry is explored on silicon nitride (Si(3)N(4)) surfaces as an effective way for oriented immobilization of biomolecules. An ω-unsaturated ester was grafted onto Si(3)N(4) using UV irradiation. Hydrolysis followed by carbodiimide-mediated activation yielded surface-bound active succinimidyl and pentafluorophenyl ester groups. These reactive surfaces were employed for the attachment of bicyclononyne with an amine spacer, which subsequently enabled room temperature strain-promoted azide-alkyne cycloaddition (SPAAC). This stepwise approach was characterized by means of static water contact angle, X-ray photoelectron spectroscopy, and fluorescence microscopy. The surface-bound SPAAC reaction was studied with both a fluorine-tagged azide and an azide-linked lactose, yielding hydrophobic and bioactive surfaces for which the presence of trace amounts of Cu ions would have been problematic. Additionally, patterning of the Si(3)N(4) surface using this metal-free click reaction with a fluorescent azide is shown. These results demonstrate the ability of the SPAAC as a generic tool for anchoring complex molecules onto a surface under extremely mild, namely ambient and metal-free, conditions in a clean and relatively fast manner.
Langmuir 05/2012; 28(23):8651-63. · 4.19 Impact Factor
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ABSTRACT: Natural products chemistry has witnessed many new developments in the last 5years like extractions with subcritical water
and ionic liquids, LC/HRMS and LC/SPE/cryo-NMR, UHPLC, TLC/MS, MS-based preparative HPLC, comprehensive chromatography (GC×GC,
LC×LC), high-throughput screening, introduction of monolithic columns, miniaturisation, and automated structure identification.
Nevertheless identifying bioactive constituents in complex plant extracts remains a tedious process. The classical approach
of bioassay guided fractionation is time-consuming while off-line screening of extracts does not provide information on individual
compounds and sometimes suffers from false positives or negatives. One way out of this is by coupling chromatography with
chemical or biochemical assays, so called high resolution screening. An example is the development of HPLC on-line assays
for antioxidants. By the post-column addition of a relatively stable coloured radical like DPPH• or ABTS•+, radical scavengers are detected as negative peaks because in a reaction coil they reduce the model radical to its reduced,
non-coloured form. When combined with LC/DAD/MS and LC/SPE/NMR, reliable identification of active constituents becomes possible
without the necessity of ever isolating them in a classical sense. Also for finding leads for new drugs, combining HPLC with
biochemical assays is interesting but technically more difficult. Most enzymes do not work at the organic modifier concentrations
commonly encountered in RP-HPLC and the reaction time is often longer requiring dilution and lengthy coils respectively. Therefore,
new techniques have to be implemented to gain the required sensitivity for on-line enzyme assays. For stable analytes, high
temperature LC offers a solution to the organic modifier problem. When enzymes are highly expensive, like those used in the
screening for Cytochrome P450 inhibitors, miniaturisation to chip format may offer a way out. Microreactors (chips) are not
only useful for miniaturising larger assays but also offer completely new prospects in phytochemical analysis. One such application
is in the sample clean-up of acids and bases like alkaloids. In a lay-out of three parallel channels of 100μm width with
the middle one containing organic phase and the two outer ones water of high pH (feed phase) and low pH (trapping phase) such
a chip replaces two classical LLE steps but is much faster and requires less solvents and less manpower input.
Phytochemistry Reviews 04/2012; 8(2):387-399. · 4.33 Impact Factor
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ABSTRACT: After ingestion, products containing Chinese star anise (Illicium verum) contaminated or adulterated with Japanese star anise (Illicium anisatum) or other Illicium species, can cause epilepsy, hallucinations, and nausea due to the rare neurotoxic sesquiterpene dilactone anisatin that is present in Japanese star anise. Thus a rapid, simple and unambiguous method for distinguishing between the morphologically similar Chinese star anise and toxic Japanese star anise is important for food safety issues. Direct Analysis in Real Time (DART) ambient ionisation coupled with orbitrap high resolution mass spectrometry allowed the recording of mass spectra of anisatin in solid star anise fruits in seconds without any prior sample pretreatment. Spectra could be obtained in both positive ([M+NH(4)](+) at m/z 346.1496, C(15)H(24)NO(8)) and negative mode ([M-H](-) at m/z 327.1074, C(15)H(19)O(8)) and gave the same outcome provided a mass resolution of at least 27,000 is available. The anisatin signal was typically >1000 times larger in Japanese star anise than in Chinese star anise thus allowing an unequivocal qualitative determination. Herbal teas containing star anise fragments too small to be visually recognised, could be analysed by preparing a tea in 6min and subsequently sampling ∼2μL of tea on a glass rod. None of the 8 investigated retail teas contained significant quantities of anisatin. Spiking a complex herbal tea containing Chinese star anise with an equally concentrated tea prepared from Japanese star anise provided a linear calibration curve (R(2)≥0.995) after normalising on a native constituent of Chinese star anise (standard addition method). This showed that adulteration down to 1% (w/w) is still measurable. Compared with existing PCR, TLC, GC-MS and HPLC-ESI-MS/MS procedures, the proposed DART-HRMS procedure is faster and simpler and moreover measures the actual biotoxin.
Journal of chromatography. A 03/2012; 1259:179-86. · 4.19 Impact Factor
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ABSTRACT: An on-line HPLC (high performance liquid chromatography) method for the rapid screening of individual antioxidants in mixtures was developed using crocin as a substrate (i.e. oxidation probe) and 2,2'-azobis(2-amidinopropane dihydrochloride (AAPH)) in phosphate buffer (pH 7.5) as a radical generator. The polyene structure of crocin and AAPH-derived peroxyl radicals resemble the lipidic substrates and radicals found in true food more closely than the popular, albeit artificial, DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS(+) (2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate)) do. After separation by a C18 (octadecyl silica) column and UV (ultraviolet) detection, antioxidative analytes react with peroxyl radicals at 90°C and the inhibition of crocin oxidation (i.e. bleaching) is detected as a positive peak by an absorbance detector at 440 nm. The method is simple, uses standard instruments and inexpensive reagents. It can be applied for isocratic HPLC runs using mobile phases containing 10-90% organic solvent in water, weak acids or buffers (pH 3.5-8.5). With baseline correction, gradient runs are also feasible. The radical scavenging activity of several natural antioxidants and a green tea extract was studied. After optimisation of conditions such as reagent concentrations and flows, the limit of detection varied from 0.79 to 7.4 ng, depending on the antioxidant.
Journal of chromatography. A 03/2012; 1237:80-5. · 4.19 Impact Factor
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ABSTRACT: In the past decades, there has been a renewed interest in the use of natural dye plants for textile dyeing, e.g. Reseda luteola (weld). Its main yellow dye constituents are the flavones luteolin-7,3'-O-diglucoside, luteolin-7-O-glucoside and luteolin. The aim of this work was to develop a simple validated industrially usable quantitative method to assess the flavone content of R. luteola samples. The flavones were overnight extracted from the dried and ground aerial parts of the plant at room temperature via maceration with methanol-water 8:2. Afterwards, they were quantified through internal standardisation against chrysin by RP-HPLC-UV at 345 nm. The efficiency of the one-step extraction was 95%. The limits of detection (LOD) and quantitation (LOQ) were ≤ 1 ng and ≤ 3 ng, respectively, providing ample sensitivity for the purpose. The precision expressed as relative standard deviation of the entire method was <6.5% for the combined content of luteolin-7,3'-O-diglucoside, luteolin-7-O-glucoside and luteolin. The average absolute recovery (accuracy) at three spiking levels was 102% (range: 98-107%) and the relative recovery ranged from 99 to 102%. The separation was initially carried out on a traditional 250 mm × 4.6 mm 5 μm HPLC column (80 min run time, 35.9 mL MeOH). It was then speeded up by the use of a 50 mm × 3.0mm 1.8 μm UHPLC column (5 min run time, 1.4 mL MeCN), while still using a conventional HPLC system. Whereas, the retention times on the UHPLC column were relatively less reproducible, cross-validation showed that the quantitation of luteolin-7,3'-O-diglucoside, luteolin-7-O-glucoside and luteolin was not statistically significantly different, with comparable precision. The method using the UHPLC column is more sensitive. The analytical method described meets the demand for a very small manpower input per sample and uses standard laboratory equipment. Usage of short UHPLC columns opens up interesting possibilities for modernising HPLC-based phytochemical analyses.
Journal of chromatography. A 11/2011; 1218(47):8544-50. · 4.19 Impact Factor
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ABSTRACT: Alkaloid-containing plants are an intrinsic part of the regular Western diet. The present paper summarizes the occurrence of alkaloids in the food chain, their mode of action and possible adverse effects including a safety assessment. Pyrrolizidine alkaloids are a reason for concern because of their bioactivation to reactive alkylating intermediates. Several quinolizidine alkaloids, β-carboline alkaloids, ergot alkaloids and steroid alkaloids are active without bioactivation and mostly act as neurotoxins. Regulatory agencies are aware of the risks and have taken or are considering appropriate regulatory actions for most alkaloids. These vary from setting limits for the presence of a compound in feed, foods and beverages, trying to define safe upper limits, advising on a strategy aiming at restrictions in use, informing the public to be cautious or taking specific plant varieties from the market. For some alkaloids known to be present in the modern food chain, e.g., piperine, nicotine, theobromine, theophylline and tropane alkaloids risks coming from the human food chain are considered to be low if not negligible. Remarkably, for many alkaloids that are known constituents of the modern food chain and of possible concern, tolerable daily intake values have so far not been defined.
Molecular Nutrition & Food Research 08/2011; 56(1):30-52. · 4.30 Impact Factor
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Angewandte Chemie International Edition 06/2011; 50(24):5428-30. · 13.45 Impact Factor
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Kishore K R Tetala,
Astrid P Heikema,
Aliaksei V Pukin,
Carel A G M Weijers,
Anne P Tio-Gillen,
Michel Gilbert,
Hubert P Endtz,
Alex van Belkum,
Han Zuilhof,
Gerben M Visser,
Bart C Jacobs, Teris A van Beek
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ABSTRACT: Monolithic columns containing ganglioside GM2 and GM3 mimics were prepared for selective removal of serum anti-ganglioside antibodies from patients with acute and chronic immune-mediated neuropathies. ELISA results demonstrated that anti-GM2 IgM antibodies in human sera and a mouse monoclonal anti-GM2 antibody were specifically and selectively adsorbed by monolithic GM2 mimic columns and not by blank monolithic columns or monolithic GM3 mimic columns. In control studies, serum antibodies against the ganglioside GQ1b from another neuropathy patient were not depleted by monolithic GM2 mimic columns. Fluorescence microscopy with FITC-conjugated anti-human immunoglobulin antibodies showed that the immobilized ganglioside mimics were evenly distributed along the column. The columns were able to capture ∼95% of the anti-GM2 antibodies of patients after only 2 min of incubation. A monolithic column of 4.4 μL can deplete 28.2 μL of undiluted serum. These columns are potential diagnostic and therapeutic tools for neuropathies related to anti-ganglioside antibodies.
Journal of Medicinal Chemistry 05/2011; 54(10):3500-5. · 4.80 Impact Factor
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ABSTRACT: Affinity chromatography on monolithic supports is a powerful analytical chemical platform because it allows for fast analyses, small sample volumes, strong enrichment of trace biomarkers and applications in microchips. In this review, the recent research using monolithic materials in the field of bioaffinity chromatography (including immunochromatography) is summarized and discussed. After giving an introduction into affinity chromatography, information on different biomolecules (antibodies, enzymes, lectins, aptamers) that can act as ligands in bioaffinity chromatography is presented. Subsequently, the history of monoliths, their advantages, preparation and formats (disks, capillaries and microchips) as well as ligand immobilization techniques are mentioned. Finally, analytical and preparative applications of bioaffinity chromatography on monoliths are presented. During the last four years 37 papers appeared. Protein A and G are still most often used as ligands for the enrichment of immunoglobulins. Antibodies and lectins remain popular for the analysis of mainly smaller molecules and saccharides, respectively. The highly porous cryogels modified with ligands are applied for the sorting of different cells or bacteria. New is the application of aptamers and phages as ligands on monoliths. Convective interaction media (epoxy CIM disks) are currently the most used format in monolithic bioaffinity chromatography.
Journal of Separation Science 02/2010; 33(3):422-38. · 2.73 Impact Factor
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ABSTRACT: For the first time, a microchannel was photochemically patterned with a functional linker. This simple method was developed for the site-specific attachment of DNA via this linker onto silicon oxide surfaces (e.g., fused silica and borosilicate glass), both onto a flat surface and onto the inside of a fused silica microchannel. Sharp boundaries in the micrometer range between modified and unmodified zones were demonstrated by the attachment of fluorescently labeled DNA oligomers. Studies of repeated hybridization-dehybridization cycles revealed selective and reversible binding of cDNA strands at the explicit locations. On average, approximately 7 x 10(11) fluorescently labeled DNA molecules were hybridized per square centimeter. The modified surfaces were characterized with X-ray photoelectron spectroscopy, infrared microscopy, static contact angle measurements, confocal laser scanning microscopy, and fluorescence detection (to quantify the attachment of the fluorescently labeled DNA).
Langmuir 12/2009; 25(24):13952-8. · 4.19 Impact Factor
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ABSTRACT: Phenolic esters like chlorogenic acid play an important role in therapeutic properties of many plant extracts. We aimed to produce phenolic esters in baker's yeast, by expressing tobacco 4CL and globe artichoke HCT. Indeed yeast produced phenolic esters. However, the primary product was identified as N-(E)-p-coumaroyl-3-hydroxyanthranilic acid by NMR. This compound is an amide condensation product of p-coumaric acid, which was supplied to the yeast, with 3-hydroxyanthranilic acid, which was unexpectedly recruited from the yeast metabolism by the HCT enzyme. N-(E)-p-coumaroyl-3-hydroxyanthranilic acid has not been described before, and it shows structural similarity to avenanthramides, a group of inflammation-inhibiting compounds present in oat. When applied to mouse fibroblasts, N-(E)-p-coumaroyl-3-hydroxyanthranilic acid induced a reduction of intracellular reactive oxygen species, indicating a potential therapeutic value for this novel compound.
Metabolic Engineering 11/2009; 12(3):223-32. · 5.61 Impact Factor
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ABSTRACT: An on-line method for the rapid pinpointing of radical scavengers in non-polar mixtures like vegetable oils was developed. To avoid problems with dissolving the sample, normal-phase chromatography on bare silica gel was used with mixtures of hexane and methyl tert-butyl ether as the eluent. The high performance liquid chromatography-separated analytes are mixed post-column with a solution of stable free radicals in hexane. Reduced levels of the radical as a result of a reaction with a radical scavenger are detected as negative peaks by an absorbance detector. After investigating a number of different reagents, solvents, concentrations and solution flow rates an optimized instrumental set-up incorporating a superloop for pulse-free delivery of the reagent solution is presented. Both 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and 2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy (galvinoxyl) were used as stable free radicals. The method is suitable for both isocratic and gradient HPLC operation. The method has a simple experimental protocol, uses standard instruments and inexpensive and stable reagents, and accepts any hexane-soluble sample. It can also be used for semi-quantitative analysis. The method was applied to several pure, non-polar natural antioxidants, vegetable oils and lipid-soluble rosemary extract. The limits of detection varied from 0.2 to 176 microg/ml, depending on the compound tested.
Journal of chromatography. A 09/2009; 1216(43):7268-74. · 4.19 Impact Factor
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ABSTRACT: A three-phase microchip was developed for the rapid and efficient small-scale purification of alkaloids from plant extracts. As part of the development of such a three-phase microchip, first a two-phase microchip with two channels (3.2 cm and 9.3 cm) was used to study the extraction efficiency of strychnine nitrate and strychnine at various flow rates. Strychnine was extracted from a basic aqueous phase to a chloroform phase (extraction) or strychnine was extracted from a chloroform phase into an acidic aqueous phase (back extraction). Subsequently, the "simultaneous extraction and back extraction" of strychnine was carried out in a three-phase microchip. The experimental extraction rate and yield were compared with model data. At a residence time of 25 sec, 79.5% of strychnine was extracted into the acidic aqueous phase using the three-phase microchip. In general, a good correlation was found between experimental results and model data for both two- and three-phase extractions. Finally, the three-phase microchip was employed in the purification of alkaloids (strychnine and brucine) from Strychnos seed extracts.
Lab on a Chip 08/2009; 9(14):2085-92. · 5.67 Impact Factor
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ABSTRACT: The chemical analysis and quality control of Ginkgo leaves, extracts, phytopharmaceuticals and some herbal supplements is comprehensively reviewed. The review is an update of a similar, earlier review in this journal [T.A. van Beek, J. Chromatogr. A 967 (2002) 21-55]. Since 2001 over 3000 papers on Ginkgo biloba have appeared, and about 400 of them pertain to chemical analysis in a broad sense and are cited herein. The more important ones are discussed and, where relevant, compared with the best methods published prior to 2002. In the same period over 2500 patents were filed on Ginkgo and the very few related to analysis are mentioned as well. Important constituents include terpene trilactones, i.e. ginkgolide A, B, C, J and bilobalide, flavonol glycosides, biflavones, proanthocyanidins, alkylphenols, simple phenolic acids, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols. In the most common so-called "standardised" Ginkgo extracts and phytopharmaceuticals several of these classes are no longer present. About 130 new papers deal with the analysis of the terpene trilactones. They are mostly extracted with methanol or water or mixtures thereof. Supercritical fluid extraction and pressurised water extraction are also possible. Sample clean-up is mostly by liquid-liquid extraction with ethyl acetate although no sample clean-up at all in combination with LC/MS/MS is gaining in importance. Separation and detection can be routinely carried out by RP-HPLC with ELSD, RI or MS, or by GC/FID or GC/MS after silylation. Hydrolysis followed by LC/MS allows the simultaneous analysis of terpene trilactones and flavonol aglycones. No quantitative procedure for all major flavonol glycosides has yet been published because they are not commercially available. The quantitation of a few available glycosides has been carried out but does not serve a real purpose. After acidic hydrolysis to the aglycones quercetin, kaempferol and isorhamnetin and separation by HPLC, quantitation is straightforward and yields by recalculation an estimation of the original total flavonol glycoside content. A profile of the genuine flavonol glycosides can detect poor storage or adulteration. Although the toxicity of Ginkgo alkylphenols upon oral administration has never been undoubtedly proven, most suppliers limit their content in extracts to 5 ppm and dozens of papers on their analysis were published. One procedure in which a methanolic extract is directly injected on a C8 HPLC column appears superior in terms of sensitivity (<5 ppm), separation, simplicity and validation and will be incorporated in the European Pharmacopoeia. Alternatively GC/MS and ELISA methods can be used. A sharp contrast to the plethora of papers on terpene trilactones, flavonol glycosides, and ginkgolic acids forms the low number of papers on biflavones, proanthocyanidins, simple phenolics, simple acids, and other constituents that make up the remaining 70% of Ginkgo standardised extracts. More research in this direction is clearly needed. For the analysis of Ginkgo proanthocyanidins (7%) for instance, no reliable assays are yet existing. Finally the growing literature on pharmacokinetic and fingerprinting studies of Ginkgo is briefly summarised.
Journal of chromatography. A 01/2009; 1216(11):2002-32. · 4.19 Impact Factor
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ABSTRACT: Screening for antioxidants requires simple in vitro model systems to investigate antioxidant activity. High resolution screening (HRS), combining a separation technique like HPLC with fast post-column (bio)chemical detection can rapidly pinpoint active compounds in complex mixtures. In this paper both electrochemical and chemistry-based assays are reviewed and discussed. The focus is on the mechanisms involved and differences between the assays, rather than on the matrix or analytes. With 45 applications high resolution antioxidant screening has now become an almost routine tool for the rapid identification of antioxidants in plant extracts, foods and beverages. The methods based on true reactive oxygen species (ROS) provide the most realistic measure of antioxidant activity. Unfortunately these methods are difficult to set up and control and have not been applied since they were reported. The methods based on electrochemical detection are more practical, but have still received only limited attention for practical screening purposes. The methods based on a single relatively stable reagent such as DPPH and ABTS(+) have become most popular, because of their simple set-up and ease of control. The methods have been combined with on-line DAD, MS and NMR detection for rapid identification of active constituents.
Journal of Chromatography 10/2008; 1210(2):121-34. · 4.53 Impact Factor
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ABSTRACT: An improved comprehensive two-dimensional (LC x LC) HPLC system for the analysis of triacylglycerols was developed. In the first-dimension, a Ag(I)-coated cation exchanger (250 mm x 2.1 mm, 5 microm) was employed with a gradient from 100% MeOH to 6% MeCN in MeOH at 20 microL/min. Using a 10-way valve with two switching loops, 1 min sections of the first-dimension were introduced in the second-dimension consisting of a 30 mm x 4.6 mm C18 (1.8 microm) column with an isocratic mobile phase of methanol-methyl tert-butyl ether (70:30) at 3.0 mL/min. As the second-dimension solvent was stronger than the first-dimension solvent, focusing in the second-dimension took place, leading to better separations than in previously reported analyses in which hexane was the main constituent of the first-dimension eluent. Compounds differing by 2 in their partition number were baseline separated in the second-dimension. Detection took place by UV at 210 nm, evaporative light scattering and (+)-atmospheric pressure chemical ionisation-MS with the latter giving the best results. Corn oil was investigated and 44 compounds could be detected: 34 triacylglycerols (TAGs), 8 oxygenated TAGs, and 2 TAGs containing a trans double bond. Data manipulation allowed the construction of contour plots and the automated calculation of the first- and second-dimension retention times and peak areas. Quantitative results are compared with a fatty acid methyl ester analysis, and with literature data.
Journal of Chromatography 02/2008; 1178(1-2):43-55. · 4.53 Impact Factor
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Yu Tong Qiu,
Renate C Smallegange,
Braak Cajo J F Ter,
Jeroen Spitzen,
Joop J A Van Loon,
Musa Jawara,
Paul Milligan,
Agnes M Galimard, Teris A Van Beek,
Bart G J Knols,
Willem Takken
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ABSTRACT: Chemical cues play an important role in the host-seeking behavior of blood-feeding mosquitoes (Diptera: Culicidae). A field study was carried out in The Gambia to investigate the effects of human odor or synthetic odor blends on the attraction of mosquitoes. MM-X traps baited with 16 odor blends to which carbon dioxide (CO2) was added were tested in four sets of experiments. In a second series of experiments, MM-X traps with 14 odor blends without CO2 were tested. A blend of ammonia and L-lactic acid with or without CO2 was used as control odor in series 1 and 2, respectively. Centers for Disease Control and Prevention (CDC) traps were placed in a traditional house and an experimental house to monitor mosquito densities during the experiments. The MM-X traps caught a total number of 196,756 mosquitoes, with the most abundant species belonging to the genera Mansonia (70.6%), Anopheles (17.5%), and Culex (11.5%). The most abundant mosquito species caught by the CDC traps (56,290 in total) belonged to the genera Mansonia (59.4%), Anopheles (16.0% An. gambiae s.l. Giles, and 11.3% An. ziemanni Grünberg), and Culex (11.6%). MM-X traps baited with synthetic blends were in many cases more attractive than MM-X traps baited with human odors. Addition of CO2 to synthetic odors substantially increased the catch of all mosquito species in the MM-X traps. A blend of ammonia + L-lactic acid + CO, + 3-methylbutanoic acid was the most attractive odor for most mosquito species. The candidate odor blend shows the potential to enhance trap collections so that traps will provide better surveillance and possible control.
Journal of Medical Entomology 12/2007; 44(6):970-83. · 1.76 Impact Factor
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ABSTRACT: Carbohydrate monolithic beds were synthesized in a single step in capillary columns to study affinity chromatography of lectins. In this method, carbohydrates (beta-galactose, beta-glucose, and alpha-mannose) with an easy to synthesize alkene terminated tetraethylene glycol spacer were used as functional monomers along the monomer 2-hydroxyethyl methacrylate (HEMA). As crosslinkers (+)-N,N'-diallyltartardiamide (DATD) and piperazine diacrylamide (PDA, 1,4-bisacryloyl-piperazine) were used. SEM showed the successful formation of monolithic beds in the capillary columns. The permeability of the columns was high. The specific interaction of the lectins Con A, Lens culinaris (LCA) and Arachis hypogaea (PNA) with the carbohydrate stationary phase was studied by frontal affinity chromatography (FAC). Con A and LCA were successfully eluted from the column using 0.1 M methyl-alpha-mannopyranoside and PNA with 0.1 M beta-galactose. Dissociation constants (Kd) for carbohydrate-lectin interactions were determined and compared with literature.
Journal of Separation Science 12/2007; 30(17):2828-35. · 2.73 Impact Factor
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ABSTRACT: A quantitative 1H NMR procedure for the determination of bilobalide and ginkgolides A, B, C and J in Ginkgo biloba leaves and in phytopharmaceuticals without prior chromatographic separation of the mixture has been developed. The method is based on the comparison of the integral of each H-12 proton of the five ginkgo terpene trilactones with that of the olefinic protons of the internal standard (maleic acid). These protons are all well separated at 200 MHz and occur in a less crowded region of the NMR spectrum (6.15-6.50 ppm). The selectivity, reproducibility and sensitivity are comparable with high pressure liquid chromatography (HPLC) with refractive index (RI) detection. The minimum amount that can be quantified within 30 min at 200 MHz is approximately 0.1 mg for all four ginkgolides and bilobalide. Advantages, in comparison with HPLC-RI, are that no reference substances are needed and that for the occasional analysis of a limited number of samples a very significant time-gain can be achieved.
Phytochemical Analysis 03/2007; 4(6):261 - 268. · 2.63 Impact Factor
