Skip to content. Skip to navigation
Sections
Personal tools
You are here: Home
Featured Journal
Navigation
Site Search
 
Search only the current folder (and sub-folders)
Log in


Forgot your password?
New user?
Check out our New Publishers' Select for Free Articles
Journal Search

Analytical and Bioanalytical Chemistry (v.389, #6)


Pesticides in Food by Amadeo R. Fernández-Alba; Ana Agüera (pp. 1661-1661).
is Professor of Analytical Chemistry at the University of Almería, Spain. He has been involved in research related to the application of hyphenated mass spectrometric methods in pharmaceutical, environmental, and food analysis He is also a member of the Advisory Group of the European Analytical Quality-Control Group and co-Head of the European Community Reference Laboratory for Pesticide Residues in Fruits and Vegetables at the University of Almería. has been a Professor in the Department of Hydrogeology and Analytical Chemistry at the University of Almería (Spain) since 1995. Her professional experience in research is on method development and monitoring of pesticides and other priority and emerging organic pollutants in food and environmental samples by advanced mass spectrometric techniques.

Methods of sample preparation for determination of pesticide residues in food matrices by chromatography–mass spectrometry-based techniques: a review by Dimitra A. Lambropoulou; Triantafyllos A. Albanis (pp. 1663-1683).
Much progress has been made in pesticide analysis over the past decade, during which time hyphenated techniques involving highly efficient separation and sensitive detection have become the techniques of choice. Among these, methods based on chromatographic separation with mass spectrometric detection have resulted in greater likelihood of identification and are acknowledged to be extremely useful and authoritative methods for determination of pesticide residues. Even with such powerful instrumental techniques, however, the risk of interference increases with the complexity of the matrix studied, so sample preparation before instrumental analysis is still mandatory in many applications, for example food analysis. This article summarizes the analytical characteristics of the different methods of sample-preparation for determination of pesticide residues in a variety of food matrices, and surveys their recent applications in combination with chromatographic mass spectrometric analysis. We discuss the advantages and the disadvantages of the different methods, address instrumental aspects, and summarize conclusions and perspectives for the future.

Keywords: Pesticides; Sample preparation; Chromatography–mass spectrometry; Food analysis


Development and validation of a multi-residue method for the determination of pesticides in processed fruits and vegetables using liquid chromatography–electrospray ionization tandem mass spectrometry by Helen Botitsi; Anastasios Economou; Despina Tsipi (pp. 1685-1695).
A sensitive multi-residue analytical method, utilizing ethyl acetate extraction and liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS), has been developed and validated for simultaneous determination of 28 pesticides of different chemical classes (polar organophosphates, carbamates, strobilurines, neonicotinoids, amides, pyrimidines, benzimidazoles, imidazoles and triazoles), and their transformation products, in processed fruit and vegetables. Two precursor–product ion transitions were monitored for each pesticide in selected reaction monitoring (SRM) mode. Linearity (r 2 ≥ 0.99) was good over the concentration range 0.5 to 100 μg L−1 for all the pesticides, and instrumental detection limits ranged from 0.1 to 1 μg L−1. Mean recovery for fruit and vegetables spiked at 0.010 mg kg−1 ranged from 65 to 94.4%, and relative standard deviations ranged from 9.0 to 20.0%. When the amount spiked was 0.050 mg kg−1 recoveries ranged from 72.5 to 90% and relative standard deviations were from 6.1 to 19.0%. Method detection limits were from 0.002 to 0.007 mg kg−1 for the different food matrices studied. The method was used to monitor pesticide residues in a wide variety of fruits and vegetables.

Keywords: LC–ESI-MS–MS; Multi-residue; Pesticides; Validation; Fruits; Vegetables


Analysis of pesticide residues using the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) pesticide multiresidue method in combination with gas and liquid chromatography and tandem mass spectrometric detection by Paula Payá; Michelangelo Anastassiades; Dorothea Mack; Irina Sigalova; Bünyamin Tasdelen; José Oliva; Alberto Barba (pp. 1697-1714).
The Quick Easy Cheap Effective Rugged and Safe multiresidue method (QuEChERS) has been validated for the extraction of 80 pesticides belonging to various chemical classes from various types of representative commodities with low lipid contents. A mixture of 38 pesticides amenable to gas chromatography (GC) were quantitatively recovered from spiked lemon, raisins, wheat flour and cucumber, and determined using gas chromatography–tandem mass spectrometry (GC–MS/MS). An additional mixture of 42 pesticides were recovered from oranges, red wine, red grapes, raisins and wheat flour, using liquid chromatography–tandem mass spectrometry (LC–MS/MS) for determination. The pesticides chosen for this study included many of the most frequently detected ones and/or those that are most often found to violate the maximum residue limit (MRL) in food samples, some compounds that have only recently been introduced, as well as a few other miscellaneous compounds. The method employed involved initial extraction in a water/acetonitrile system, an extraction/partitioning step after the addition of salt, and a cleanup step utilizing dispersive solid-phase extraction (D-SPE); this combination ensured that it was a rapid, simple and cost-effective procedure. The spiking levels for the recovery experiments were 0.005, 0.01, 0.02 and 0.2 mg kg−1 for GC–MS/MS analyses, and 0.01 and 0.1 mg kg−1 for LC–MS/MS analyses. Adequate pesticide quantification and identity confirmation were attained, even at the lowest concentration levels, considering the high signal-to-noise ratios, the very good accuracies and precisions, as well as the good matches between the observed ion ratios. Mean recoveries mostly ranged between 70 and 110% (98% on average), and relative standard deviations (RSD) were generally below 10% (4.3% on average). The use of analyte protectants during GC analysis was demonstrated to provide a good alternative to the use of matrix-matched standards to minimize matrix-effect-related errors. Based on these results, the methodology has been proven to be highly efficient and robust and thus suitable for monitoring the MRL compliance of a wide range of commodity/pesticide combinations. Figure QuEChERS for fruits and vegetables

Keywords: QuEChERS; Pesticides; GC–MS/MS; LC–MS/MS; Analyte protectants; Fruits and vegetables; Matrix effects; Wine


Modification and re-validation of the ethyl acetate-based multi-residue method for pesticides in produce by Hans G. J. Mol; Astrid Rooseboom; Ruud van Dam; Marleen Roding; Karin Arondeus; Suryati Sunarto (pp. 1715-1754).
The ethyl acetate-based multi-residue method for determination of pesticide residues in produce has been modified for gas chromatographic (GC) analysis by implementation of dispersive solid-phase extraction (using primary–secondary amine and graphitized carbon black) and large-volume (20 μL) injection. The same extract, before clean-up and after a change of solvent, was also analyzed by liquid chromatography with tandem mass spectrometry (LC–MS–MS). All aspects related to sample preparation were re-assessed with regard to ease and speed of the analysis. The principle of the extraction procedure (solvent, salt) was not changed, to avoid the possibility invalidating data acquired over past decades. The modifications were made with techniques currently commonly applied in routine laboratories, GC–MS and LC–MS–MS, in mind. The modified method enables processing (from homogenization until final extracts for both GC and LC) of 30 samples per eight hours per person. Limits of quantification (LOQs) of 0.01 mg kg−1 were achieved with both GC–MS (full-scan acquisition, 10 mg matrix equivalent injected) and LC–MS–MS (2 mg injected) for most of the pesticides. Validation data for 341 pesticides and degradation products are presented. A compilation of analytical quality-control data for pesticides routinely analyzed by GC–MS (135 compounds) and LC–MS–MS (136 compounds) in over 100 different matrices, obtained over a period of 15 months, are also presented and discussed. At the 0.05 mg kg−1 level acceptable recoveries were obtained for 93% (GC–MS) and 92% (LC–MS–MS) of pesticide–matrix combinations.

Keywords: Foods/Beverages; Pesticides; GC-MS; LC-MS/MS; Multi-residue analysis


Comprehensive gas chromatography coupled to mass spectrometry for the separation of pesticides in a very complex matrix by Luigi Mondello; Alessandro Casilli; Peter Quinto Tranchida; Maria Lo Presti; Paola Dugo; Giovanni Dugo (pp. 1755-1763).
The present research is focused on the development of a comprehensive two-dimensional gas chromatography–rapid scanning quadrupole mass spectrometric (GC x GC-qMS) methodology for the analysis of trace-amount pesticides contained in a complex real-world sample. Reliable peak assignment was carried out by using a recently developed, dedicated pesticide MS library (for comprehensive GC analysis), characterized by a twin-filter search procedure, the first based on a minimum degree of spectral similarity and the second on the interactive use of linear retention indices (LRI). The library was constructed by subjecting mixtures of commonly used pesticides to GC x GC-qMS analysis and then deriving their pure mass spectra and LRI values. In order to verify the effectiveness of the approach, a pesticide-contaminated red grapefruit extract was analysed. The certainty of peak assignment was attained by exploiting both the enhanced separation power of dual-oven GC x GC and the highly effective search procedure.

Keywords: Pesticides; Comprehensive two-dimensional gas chromatography; GC x GC; Rapid scanning quadrupole mass spectrometry; Red grapefruit


Multiresidue pesticide analysis of fruits by ultra-performance liquid chromatography tandem mass spectrometry by O. J. Pozo; M. Barreda; J. V. Sancho; F. Hernández; J. Ll. Lliberia; M. A. Cortés; B. Bagó (pp. 1765-1771).
Ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC–MS–MS) has been used for screening and quantification of 32 pesticides and metabolites in two fruit matrices. The compounds investigated belonged to different chemical families of insecticides, acaricides, fungicides, and herbicides; several metabolites were also included. Quantification was conducted using matrix-matched standards calibration; response was a linear function of concentration in the range tested (10–500 ng mL−1). The method was validated with blank samples of lemon and raisin spiked at 0.01 and 0.1 mg kg−1, and recoveries were satisfactory, between 70 and 110%, for most of the pesticides tested and relative standard deviations were below 15% (n = 5 at each spiking level). Excellent sensitivity resulted in limits of detection for all compounds well below 0.01 mg kg−1, with the limit of quantification being validated at 0.01 mg kg−1. The UPLC system generates narrow peaks (approx. 5 s), thus increasing peak height and improving sensitivity. This improved separation efficiency facilitates adequate resolution not only of the analytes but also of matrix interferences compared with conventional HPLC. The method developed could also resolve some geometric isomers. The main advantage of this approach is the high sample throughput achieved because of the short analysis time, which enables satisfactory separation of all the compounds in less than 5 min per sample.

Keywords: UPLC; Pesticides; Metabolites; Multiresidue analysis; Tandem mass spectrometry; Fruits


Analysis of pesticide residues in fruit and vegetables with ethyl acetate extraction using gas and liquid chromatography with tandem mass spectrometric detection by Tuija Pihlström; Gun Blomkvist; Paula Friman; Ulla Pagard; Bengt-Göran Österdahl (pp. 1773-1789).
A multiresidue method based on extraction with ethyl acetate has been used at the Swedish National Food Administration since 1989 to monitor pesticide residues in fruit and vegetables. The method has been continuously adjusted, resulting in simple and quick analyses of pesticide residues. To recover basic pesticides, the addition of an alkali is necessary. The addition of sodium hydrogen carbonate has been shown to recover all pesticides effectively without any degradation. The liquid chromatography (LC) with tandem mass spectrometry (MS/MS) technique has made it possible to analyse more polar pesticides and to replace many single methods. The latest development in the multiresidue method, comprising the use of gas chromatography (GC) with MS/MS, has further improved the analysis by replacing the conventional GC detectors. The need for cleanup has been reduced or eliminated entirely. Consequently, the method has been simplified in a way that makes it possible to recover all included analytes in many different matrices in one single extraction and to detect them either with GC-MS/MS or with LC-MS/MS.

Keywords: Pesticides; Multiresidue analysis; GC-MS/MS and LC-MS/MS; Fruit and vegetables


Development of an analytical method for the determination of the residues of four pyrethroids in meat by GC–ECD and confirmation by GC–MS by Danilo Attard Barbini; Fabiana Vanni; Silvana Girolimetti; Roberto Dommarco (pp. 1791-1798).
The development of an analytical method for the determination of four selected pyrethroid insecticides at residue level in beef meat is presented. Acetone and petroleum ether at 40–60 °C were chosen as extraction solvents. A two-step clean-up was performed using an Extrelut NT3-C18 system followed by a Florisil column, with disposable, ready-to-use cartridges. Instrumental analysis was carried out on a gas chromatograph equipped with an electron capture detector (GC–ECD), using matrix-matched and internal standard calibration techniques. Confirmatory analysis by GC–MS was performed. Recoveries at the EU Maximum Residue Limit (MRL), 0.5 × MRL and 1.5 × MRL levels and the repeatabilities were widely satisfactory. The main advantage of the method was the reduction of analysis time as compared with previously published works. The applicability of the method to different matrices and pesticide classes will be investigated.

Keywords: Beef meat; Residues; Pyrethroid; Pesticides; GC–ECD; GC–MS


Determination of chlormequat in pig serum and sow milk by LC–MS/MS by M. E. Poulsen; H. B. Christensen; M. T. Sørensen; H. Leffers; J. H. Andersen (pp. 1799-1804).
Chlormequat is a plant growth regulator widely used on cereals, and there is general concern that it may impair human fertility. A LC–MS/MS method for the analysis of chlormequat in milk and serum was developed and validated in connection with an investigation on the effect of chlormequat on pig reproduction. Validation of the method was based on recovery tests at three spiking levels, determined as double determinations and repeated at least four times. Samples were extracted with methanol–water–acetic acid, centrifuged, filtrated and determined by LC–MS/MS. The mean recoveries were in the range 80–110%, and the LOD was 0.2 ng/g for serum and 0.3 ng/g for milk. The values for repeatability and reproducibility were within 2/3 of the limits given by the Horwitz equation. Samples of pig serum (59) and sow milk (27) were analyzed using the method. Chlormequat was determined in four milk samples in the range of 0.4 ng/g to 1.2 ng/g and in all serum samples in the range of 0.2 ng/g−4.0 ng/g.

Keywords: Pesticide; Chlormequat; Serum; Milk; LC–MS/MS


Evaluation of pesticide residue in grape juices and the effect of natural antioxidants on their degradation rate by Yolanda Picó; Cornelia Kozmutza (pp. 1805-1814).
Various studies have been drawn toward the beneficial properties of fruit juices because they have several components, such as phenols, vitamins, and flavonoids, with antioxidant effects. However, fruit juices can also contain residues of pesticides used as standard pest control methods in crops. Many of these pesticides are degraded through oxidative mechanisms, and their persistence in juices can be enhanced by antioxidants. This study covers the degradation of four pesticides, aldicarb, demeton-S-methyl, fenamiphos, and methiocarb, to their respective sulfoxide and sulfone in grape juices, water (pH 3.5) and water (pH 3.5) with quercetin (one of the most important flavonoids of grape) added in an attempt to establish whether the presence of antioxidants can affect the degradation rate of pesticides. For this purpose, a multiresidue method based on solid-phase extraction (SPE) was developed for the simultaneous determination of these pesticides and their metabolites in commercial juices. The extraction procedure was carried out in C18 columns. The subsequent elution of pesticides was performed with dichloromethane prior to the determination by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using two precursor-product ion transitions. Average recoveries for all the pesticides studied were higher than 80%, with relative standard deviations lower than 15% in the concentration range 0.005–0.05 μg/mL, and the quantification limits achieved ranged from 0.1 to 4.6 μg/L. The results demonstrated that degradation was slower in fruit juices and aqueous solutions with quercetin than in water. Several commercial grape juices were also analyzed to establish the levels of these pesticides. Methiocarb, fenamiphos, and demeton-S-methyl were found at low levels in some samples.

Keywords: Pesticide residues; Fruit juices; Natural antioxidant food components; Quercetin; Multiresidue; Liquid chromatography-mass spectrometry; Interactions between pesticides and natural food components


Application of high-performance liquid chromatography–tandem mass spectrometry with a quadrupole/linear ion trap instrument for the analysis of pesticide residues in olive oil by M. D. Hernando; C. Ferrer; M. Ulaszewska; J. F. García-Reyes; A. Molina-Díaz; A. R. Fernández-Alba (pp. 1815-1831).
This article describes the development of an enhanced liquid chromatography–mass spectrometry (LC–MS) method for the analysis of pesticides in olive oil. One hundred pesticides belonging to different classes and that are currently used in agriculture have been included in this method. The LC–MS method was developed using a hybrid quadrupole/linear ion trap (QqQLIT) analyzer. Key features of this technique are the rapid scan acquisition times, high specificity and high sensitivity it enables when the multiple reaction monitoring (MRM) mode or the linear ion-trap operational mode is employed. The application of 5 ms dwell times using a linearly accelerating (LINAC) high-pressure collision cell enabled the analysis of a high number of pesticides, with enough data points acquired for optimal peak definition in MRM operation mode and for satisfactory quantitative determinations to be made. The method quantifies over a linear dynamic range of LOQs (0.03–10 μg kg−1) up to 500 μg kg−1. Matrix effects were evaluated by comparing the slopes of matrix-matched and solvent-based calibration curves. Weak suppression or enhancement of signals was observed (<15% for most—80—of the pesticides). A study to assess the identification criteria based on the MRM ratio was carried out by comparing the variations observed in standard vs matrix (in terms of coefficient of variation, CV%) and within the linear range of concentrations studied. The CV was lower than 15% when the response observed in solvent was compared to that in olive oil. The limit of detection was ≤10 μg kg−1 for five of the selected pesticides, ≤5 μg kg−1 for 14, and ≤1 μg kg−1 for 81 pesticides. For pesticides where additional structural information was necessary for confirmatory purposes—in particular at low concentrations, since the second transition could not be detected—survey scans for enhanced product ion (EPI) and MS3 were developed.

Keywords: Pesticide residues; Olive oil; QTRAP analyzer; Quantitation; Matrix effects


Determination of pesticides in milk-based infant formulas by pressurized liquid extraction followed by gas chromatography tandem mass spectrometry by M. Mezcua; M. R. Repetti; A. Agüera; C. Ferrer; J. F. García-Reyes; A. R. Fernández-Alba (pp. 1833-1840).
An efficient and selective automated analytical method for the determination and quantification of a selected group of 12 organochlorine and organophosphorous pesticides in milk-based infant formulas has been developed. The samples were extracted by pressurized liquid extraction (PLE) and analysed using GC-MS/MS. The use of alumina as the fat retainer in the PLE extraction cell, together with the application of an injector temperature program during the GC injection process, avoided typical matrix interferences without the application of additional cleanup steps. Mean recoveries of between 70 and 110% were achieved for most of the compounds, except for chlorpyrifos methyl (50%), vinclozoline (48%), fenitrothion (56%) and procymidone (53%), with relative standard deviations ranging from 9 to 17%. Low limits of quantification were obtained for the studied compounds, from 0.01 to 2.6 μg kg−1, thus guaranteeing their accurate determination within the rigorous requirements established for baby food. The validated method was applied to a pilot monitoring study in Spain. Twenty five samples of different brands of powdered infant formulas were obtained from supermarkets. Positive findings of endosulfan I, endosulfan II, fenitrothion, chlorpyrifos ethyl and bifenthrin were detected at concentrations ranging from 0.03 to 5.03 μg kg−1.

Keywords: Baby food; Infant milk formulas; Pressurized liquid extraction; GC-MS/MS; Pesticides


Multichannel SPR biosensor for detection of endocrine-disrupting compounds by J. Dostálek; J. Přibyl; J. Homola; P. Skládal (pp. 1841-1847).
A surface plasmon resonance (SPR) biosensor for simultaneous detection of multiple organic pollutants exhibiting endocrine-disrupting activity, namely atrazine, benzo[a]pyrene, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-nonylphenol, is reported. The biosensor utilizes a multichannel SPR sensor based on wavelength modulation of SPR and wavelength division multiplexing (WDM) of sensing channels, antibodies as biorecognition element and a competitive immunoassay detection format. An analysis time of 45 min (including 30-min incubation of the sample with antibodies) and limits of detection as low as 0.05, 0.07, 0.16 and 0.26 ng mL−1 are demonstrated for benzo[a]pyrene, atrazine, 2,4-D and 4-nonylphenol, respectively. The biosensor is also shown to be regenerable and suitable for repeated use.

Keywords: Surface plasmon resonance; Immunoassays; Optical sensors; ELISA; Pesticides; Endocrine disruptors


Rapid genotyping of CYP2D6, CYP2C19 and TPMT polymorphisms by primer extension reaction in a dipstick format by Ioannis K. Litos; Evaggelia Emmanouilidou; Kyriaki M. Glynou; Eleftheria Laios; Penelope C. Ioannou; Theodore K. Christopoulos; Marilena Kampa; Elias Castanas; Achille Gravanis (pp. 1849-1857).
In recent years an increasing amount of interest has been directed at the study and routine testing of polymorphisms responsible for variations in drug metabolism. Most of the current methods involve either time-consuming electrophoresis steps or specialized and expensive equipment. In this context, we have developed a rapid, simple and robust method for genotyping of CYP2D6*3, CYP2D6*4, CYP2C19*2, CYP2C19*3 and TPMT*2 single nucleotide polymorphisms (SNP). Genomic DNA is isolated from whole blood and the segments that span the SNP of interest are amplified by PCR. The products are subjected directly (without purification) to two primer extension (PEXT) reactions (three cycles each) using normal and mutant primers in the presence of biotin-dUTP. The PEXT primers contain a (dA)30 segment at the 5′ end. The PEXT products are detected visually by a dry-reagent dipstick-type assay in which the biotinylated extension products are captured from immobilized streptavidin on the test zone of the strip and detected by hybridization with oligo(dT)-functionalized gold nanoparticles. Patient samples (76 variants in total) were genotyped and the results were fully concordant with those obtained by direct DNA sequencing.

Keywords: Pharmacogenomics; Drug-metabolizing enzymes; Genotyping; SNPs; Dry-reagent dipstick assay; PEXT


Comparison of planar SDS-PAGE, CGE-on-a-chip, and MALDI-TOF mass spectrometry for analysis of the enzymatic de-N-glycosylation of antithrombin III and coagulation factor IX with PNGase F by R. Müller; M. Marchetti; M. Kratzmeier; H. Elgass; M. Kuschel; A. Zenker; G. Allmaier (pp. 1859-1868).
Three different analytical techniques (planar SDS-PAGE, CGE-on-a-chip and MALDI-TOF-MS) applied for determination of the molecular weight of intact and partly and completely de-N-glycosylated human serum glycoproteins (antithrombin III and coagulation factor IX) have been compared. N-Glycans were removed from the protein backbone of both complex glycoproteins using PNGase F, which cleaves all types of asparagine-attached N-glycan provided the oligosaccharide has at least the length of a chitobiose core unit. Two of the applied techniques were based on gel electrophoretic separation in the liquid phase while the third technique was the gas-phase technique mass spectrometry. It was demonstrated that the enzymatic de-N-glycosylation generally worked well (completely or partially) with both glycoproteins (one containing only N-glycans and the second N- and O-glycans). All three methods were suitable for monitoring the de-N-glycosylation progress. While the molecular weights determined with MALDI-TOF-MS were most accurate, both gel electrophoretic methods provided molecular weights that were too high because of the attached glycan structures. Figure CGE-on-a-chip, SDS-PAGE and MALDI mass spectrometric pattern obtained from therapeutic glycoprotein

Keywords: Antithrombin III; Coagulation factor IX; CGE-on-a-chip; MALDI-TOF mass spectrometry; Enzymatic de-N-glycosylation


Rapid determination of pK a values of 20 amino acids by CZE with UV and capacitively coupled contactless conductivity detections by Yveline Henchoz; Julie Schappler; Laurent Geiser; Josiane Prat; Pierre-Alain Carrupt; Jean-Luc Veuthey (pp. 1869-1878).
A rapid and universal capillary zone electrophoresis (CZE) method was developed to determine the dissociation constants (pK a) of the 20 standard proteogenic amino acids. Since some amino acids are poorly detected by UV, capacitively coupled contactless conductivity detection (C4D) was used as an additional detection mode. The C4D coupling proved to be very successful on a conventional CE-UV instrument, neither inducing supplementary analyses nor instrument modification. In order to reduce the analysis time for pK a determination, two strategies were applied: (i) a short-end injection to reduce the effective length, and (ii) a dynamic coating procedure to generate a large electroosmotic flow (EOF), even at pH values as low as 1.5. As a result, the analysis time per amino acid was less than 2 h, using 22 optimized buffers covering a pH range from 1.5 to 12.0 at a constant ionic strength of 50 mM. pK a values were calculated using an appropriate mathematical model describing the relationship between effective mobility and pH. The obtained pK a values were in accordance with the literature. Figure a UV (1) and C4D (2) detectors placed on-line on the CE capillary. b Curve of effective mobility as a function of pH for histidine

Keywords: Amino acids; Capillary zone electrophoresis; Capacitively coupled contactless conductivity detection; Dissociation constants; Dynamic coating


Interaction behaviour of a PDMS–calixarene system and polar analytes characterised by microcalorimetry and spectroscopic methods by Karin Wöllner; Matthias Vollprecht; Nicolae Leopold; Maura Kasper; Stefan Busche; Günter Gauglitz (pp. 1879-1887).
Spectroscopic techniques and microcalorimetry were applied to investigate a polymer–(polydimethylsiloxane; PDMS) calixarene system during interaction with propylamine and n-propanol as analyte molecules. This was done to understand the sensitivity and selectivity of this system. By these means the interesting binding site of the calixarene selector was identified and dependencies on specific properties of the polymer and the functional groups were determined. Reflectometric interference spectroscopy (RIfS) was used to characterize the kinetics whereas isothermal titration calorimetry (ITC) yielded thermodynamic data. Infrared (IR) and 1H NMR spectroscopy allowed identification of the sensing process as an interaction between the selective group of the PDMS–calixarene system and the amino group of propylamine, and measurement of the effects on hydrogen bonds. The combination of the different spectroscopic methods and the microcalorimetric measurements broadened the understanding of this system, regarded as a model system. Thus, future tailoring of functional groups designed for improved and more selective analyte detection is possible.

Keywords: Calixarene; Infrared spectroscopy; Isothermal titration calorimetry; 1H NMR spectroscopy; Polydimethylsiloxane; Reflectometric interference spectroscopy


Comparative performance study of different sample introduction techniques for rapid and precise selenium isotope ratio determination using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS) by Nagmeddin Elwaer; Holger Hintelmann (pp. 1889-1899).
The analytical performance of five sample introduction systems, a cross flow nebulizer spray chamber, two different solvent desolvation systems, a multi-mode sample introduction system (MSIS), and a hydride generation (LI2) system were compared for the determination of Se isotope ratio measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS). The optimal operating parameters for obtaining the highest Se signal-to-noise (S/N) ratios and isotope ratio precision for each sample introduction were determined. The hydride generation (LI2) system was identified as the most suitable sample introduction method yielding maximum sensitivity and precision for Se isotope ratio measurement. It provided five times higher S/N ratios for all Se isotopes compared to the MSIS, 20 times the S/N ratios of both desolvation units, and 100 times the S/N ratios produced by the conventional spray chamber sample introduction method. The internal precision achieved for the 78Se/82Se ratio at 100 ng mL−1 Se with the spray chamber, two desolvation, MSIS, and the LI2 systems coupled to MC-ICP/MS was 150, 125, 114, 13, and 7 ppm, respectively. Instrument mass bias factors (K) were calculated using an exponential law correction function. Among the five studied sample introduction systems the LI2 showed the lowest mass bias of −0.0265 and the desolvation system showed the largest bias with −0.0321. Figure Illustration of the multi-mode sample introduction system for Se isotope ratiomeasurements

Keywords: Multi-collector inductively couple plasma mass spectrometry; Multi-mode sample introduction; Sample desolvation; Hydride generation; Selenium; Isotope ratio


Use of specific peptide biomarkers for quantitative confirmation of hidden allergenic peanut proteins Ara h 2 and Ara h 3/4 for food control by liquid chromatography–tandem mass spectrometry by M. Careri; A. Costa; L. Elviri; J.-B. Lagos; A. Mangia; M. Terenghi; A. Cereti; L. Perono Garoffo (pp. 1901-1907).
A liquid chromatography–electrospray-tandem mass spectrometry (LC–ESI-MS–MS) method based on the detection of biomarker peptides from allergenic proteins was devised for confirming and quantifying peanut allergens in foods. Peptides obtained from tryptic digestion of Ara h 2 and Ara h 3/4 proteins were identified and characterized by LC–MS and LC–MS–MS with a quadrupole-time of flight mass analyzer. Four peptides were chosen and investigated as biomarkers taking into account their selectivity, the absence of missed cleavages, the uniform distribution in the Ara h 2 and Ara h 3/4 protein isoforms together with their spectral features under ESI-MS–MS conditions, and good repeatability of LC retention time. Because of the different expression levels, the selection of two different allergenic proteins was proved to be useful in the identification and univocal confirmation of the presence of peanuts in foodstuffs. Using rice crispy and chocolate-based snacks as model food matrix, an LC–MS–MS method with triple quadrupole mass analyzer allowed good detection limits to be obtained for Ara h2 (5 μg protein g−1 matrix) and Ara h3/4 (1 μg protein g−1 matrix). Linearity of the method was established in the 10–200 μg g−1 range of peanut proteins in the food matrix investigated. Method selectivity was demonstrated by analyzing tree nuts (almonds, pecan nuts, hazelnuts, walnuts) and food ingredients such as milk, soy beans, chocolate, cornflakes, and rice crispy. Figure ESI-QTOF-MS mass spectrum of Ara h3/4 triptig digest

Keywords: Liquid-chromatography–tandem mass spectrometry; Hidden peanut allergens; Biomarker peptides


Identification of phenolic compounds from pollen extracts using capillary electrophoresis–electrospray time-of-flight mass spectrometry by D. Arráez-Román; G. Zurek; C. Bäßmann; N. Almaraz-Abarca; R. Quirantes; A. Segura-Carretero; A. Fernández-Gutiérrez (pp. 1909-1917).
In this work, a new, easy and rapid method of analyzing phenolic compounds in pollen extract, based on capillary electrophoresis coupled with electrospray ionization time-of-flight-mass spectrometry (CE–ESI–TOF–MS), has been developed. A systematic investigation of separation parameters has been performed with respect to resolution, sensitivity, analysis time and peak shape. The electrophoretic parameters and electrospray conditions must be optimized to obtain reproducible analyses. Using this method, several important phenolic compounds such as acetin-glucoside, 7-O-methylherbacetin-3-sophoroside, galloyl-glucose, quercetin-3-sophoroside, apigenin-6,8-di-C-glycoside, quercetin-3-rutinoside, genistein-7-O-β-D-glucoside, luteolin-7-O-glucoside, apigenin-7-O-glucoside and 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone have been determined directly from pollen extract. The efficiency, the rapidity, the small amounts of sample required, and the high resolution of CE coupled with the sensitivity, the selectivity, the accurate masses and the true isotopic patterns obtained using TOF-MS point to the potential of this approach for identifying the phenolic compounds present in pollen.

Keywords: Pollen; Phenolic compounds; Capillary electrophoresis; Electrospray ionization time-of-flight mass spectrometry


A catalytically active molecularly imprinted polymer that mimics peroxidase based on hemin: application to the determination of p-aminophenol by Wilney de Jesus Rodrigues Santos; Phabyanno Rodrigues Lima; César Ricardo Teixeira Tarley; Lauro Tatsuo Kubota (pp. 1919-1929).
Despite the increasing number of applications of molecularly imprinted polymers (MIP) in analytical chemistry, the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase remains as a challenge. In the current work, a new type of molecularly imprinted polymer (MIP) was synthesized with 4-aminophenol (4-APh) as the template and two monomers: hemin, which acts as the catalytic center, and methacrylic acid (MAA), which is used to build the active sites. This work shows that MIP successfully mimics peroxidase. For this purpose, a flow injection analysis system coupled to an amperometric detector was investigated through multivariate analysis. The determination of 4-APh was not affected by the equimolar presence of structurally similar phenol compounds, including catechol, 4-chloro-3-methylphenol, 2-aminophenol, guaiachol, chloroguaiachol and 2-cresol, thus highlighting the good performance of the imprinted polymer. Under the optimized experimental conditions, an analytical curve covering a wide linear response range from 0.8 up to 500 μmol L−1 (r > 0.999) was obtained, and the method gave satisfactory precisions (n = 8), as evaluated via the relative standard deviation (RSD), of 4.1 and 3.2% for solutions of 4-APh of 50 and 500 μmol L−1, respectively. Recoveries of 96–111% from water samples (tap water and river water) spiked with 4-APh were achieved, thus illustrating the accuracy of the proposed system. Figure Schematic presentation of the synthesis of the MIP

Keywords: 4-Aminophenol; Hemin; Molecularly imprinted polymers; Amperometric determination


Electroanalytical and spectroscopic procedures for examination of interactions between double stranded DNA and intercalating drugs by Anna M. Nowicka; Ewelina Zabost; Mikolaj Donten; Zofia Mazerska; Zbigniew Stojek (pp. 1931-1940).
A method is presented for the electroanalytical characterization of interactions of dsDNA with a drug, under conditions that both agents are dissolved in the phosphate buffer solution and both are electroactive. Normal pulse, square wave, differential pulse, and cyclic voltammetries were employed in the measurements of the drug and dsDNA oxidation signals at carbon electrodes. UV–Vis spectroscopy was used as a non-electrochemical method to support the electroanalytical data. An anticancer drug, C-1311 (5-diethylaminoethyl-amino-8-hydroxyimidazoacridinone), has been selected for the examination. Normal pulse voltammetry was particularly useful in showing that under the conditions employed neither dsDNA nor the drug were adsorbed at the electrode surface. Necessary conditions for the appearance of the well-defined dsDNA voltammetric signal (guanine peak) are: rigorous chemical and biological purity in the cell and appropriate purity of DNA. An analysis of the obtained results confirmed that there were two modes of interaction between C-1311 and dsDNA: by intercalation and electrostatically. In the presence of excess NaCl the electrostatic interactions deteriorate. The binding constants (K 1 and K 2, respectively) and the number (n) of nucleic base pairs (bp) and the number (m) of phosphate groups (pg) interacting with one molecule of drug have been determined. For strong interactions (intercalation) the values of the binding constant, K 1, and the binding-site size, n, equal 3.7 × 104 M−1 and 2.1, respectively. For the weak electrostatic interactions the K 2 and m parameters equal 0.28 × 104 M−1 and 4.7. The intercalation process is rather slow and its rate (the conditions of pseudo-first-order reaction) was estimated to equal 7 × 10−4 s−1. The possibility of independent determination of both interacting agents was very useful in the study. Figure Intercalation of C-1311 into a dsDNA fragment

Keywords: dsDNA; Interactions; Drugs; Voltammetry; UV–Vis spectroscopy


Determination of single photon ionization cross sections for quantitative analysis of complex organic mixtures by Thomas Adam; Ralf Zimmermann (pp. 1941-1951).
Soft single photon ionization (SPI)–time-of-flight mass spectrometry (TOFMS) is well suited for fast and comprehensive analysis of complex organic gas mixtures, which has been demonstrated in various applications. This work describes a calibration scheme for SPI, which enables quantification of a large number of compounds by only calibrating one compound of choice, in this case benzene. Photoionization cross sections of 22 substances were determined and related to the yield of benzene. These substances included six alkanes (pentane, hexane, heptane, octane, nonane, decane), three alkenes (propene, butane, pentene), two alkynes (propyne, butyne), two dienes (butadiene, isoprene), five monoaromatic species (benzene, toluene, xylene, styrene, monochlorobenzene) and NO. The cross sections of organic compounds differ by about one order of magnitude but the photoionization properties of compounds belonging to one compound class are rather similar. Therefore, the scheme can also be used for an approximate quantification of compound classes. This is demonstrated by a fast characterization and pattern recognition of two gasoline samples with different origins (Germany and South Africa) and a diesel sample (Germany). The on-line capability of the technique and the scheme is demonstrated by quantitatively monitoring and comparing the cold engine start of four vehicles: a gasoline passenger car, a diesel van, a motorbike and a two-stroke scooter.

Keywords: Single photon ionization; Cross section; Mass spectrometry; Quantification; Mineral oil products; Fuel; Car exhaust


Determination of nitro-polycyclic aromatic hydrocarbons in atmospheric aerosols using HPLC fluorescence with a post-column derivatisation technique by Olivier Delhomme; Pierre Herckes; Maurice Millet (pp. 1953-1959).
The objective of this study was to develop an efficient and sensitive analytical protocol for the determination of nitrated polycyclic aromatic hydrocarbons (NPAHs) in aerosol samples. The separation of 16 NPAH (mono-and dinitro-PAH) was achieved by reversed-phase high-performance liquid chromatography (HPLC) followed by =.28w?>on-line reduction of the NPAHs to their corresponding amino polycyclic aromatic hydrocarbons (APAHs) and quantification by fluorescence detection. The main factors affecting the on-line reduction efficiency, such as the flow rate, the temperature, the position and packing of the reduction column were evaluated and optimised. The optimal conditions obtained were: packing of the reduction column with Pt-Al2O3; a reduction column oven temperature of 90 °C; a flow rate of 0.8 mL min−1. The resulting detection limits of the method ranged between 0.06 (2 NN) and 1.25 μg L−1 (1.8 DNN), with an uncertainty of about 6%. The lifetime of the reduction column was identical to that of a typical analytical column. This analytical method was applied to particulate matter samples collected during December 2005 and August 2006 in Strasbourg (Alsace, eastern France). The NPAH concentrations observed for this urban site showed that the compounds are more abundant during winter (average of 534 pg m−3) than during summer (average of 118 pg m−3). 1-Nitropyrene was the predominant NPAH species, independent of season.

Keywords: Nitrated polycyclic aromatic hydrocarbon; Liquid chromatography coupled to fluorescence detection; On-line reduction with Pt-Al2O3 ; Particulate matter


Real-time detection of L-glutamate released from C6 glioma cells using a modified enzyme-luminescence method by S. M. Zakir Hossain; Hiroaki Shinohara; Feifei Wang; Hiromi Kitano (pp. 1961-1966).
There is an increasing interest in new strategies to detect neurotransmitters released from nerve cells in real time for brain science, drug assessment, and so on. Previously we reported real-time monitoring of dopamine release from nerve model cells by enzyme-catalyzed luminescence measurement with tyramine oxidase and peroxidase. In the present study, the system was modified with glutamate oxidase instead of tyramine oxidase to detect L-glutamate sensitively (≈ 10 nM) and rapidly with high temporal resolution (<1 s). We applied this modified method successfully to perform real-time monitoring of L-glutamate release from brain model cell (C6 glioma cell) using a luminescence plate reader upon stimulation with high concentration of KCl (>10 mM) or 5-hydroxytryptamine (>1 μM). The measurement solution was not toxic and therefore the L-glutamate release from the cell was measured by the second stimulation after exchanging the measurement solution. We conclude that the developed monitoring system is suitable for real-time detection of dynamic L-glutamate release from nerve cells in vitro and will be suitable for application in assessment of drugs acting on the nervous system. Figure Enzyme luminescence detection of L-glutamate released from cells

Keywords: Enzyme luminescence method; C6 glioma cells; L-Glutamate release; Real-time monitoring


Development of an open-tubular trypsin reactor for on-line digestion of proteins by E. C. A. Stigter; G. J. de Jong; W. P. van Bennekom (pp. 1967-1977).
A study was initiated to construct a micro-reactor for protein digestion based on trypsin-coated fused-silica capillaries. Initially, surface plasmon resonance was used both for optimization of the surface chemistry applied in the preparation and for monitoring the amount of enzyme that was immobilized. The highest amount of trypsin was immobilized on dextran-coated SPR surfaces which allowed the covalent coupling of 11 ng mm−2 trypsin. Fused-silica capillaries were modified in a similar manner and the resulting open-tubular trypsin-reactors having a pH optimum of pH 8.5, display a high activity when operated at 37 °C and are stable for at least two weeks when used continuously. Trypsin auto-digestion fragments, sample carry-over, and loss of signal due to adsorption of the protein were not observed. On-line digestion without prior protein denaturation, followed by micro-LC separation and photodiode array detection, was tested with horse-heart cytochrome C and horse skeletal-muscle myoglobin. The complete digestion of 20 pmol μL−1 horse cytochrome C was observed when the average residence time of the protein sample in a 140 cm ×50 μm capillary immobilized enzyme reactor (IMER) was 165 s. Mass spectrometric identification of the injected protein on the basis of the tryptic peptides proved possible. Protein digestion was favorable with respect to reaction time and fragments formed when compared with other on-line and off-line procedures. These results and the easy preparation of this micro-reactor provide possibilities for miniaturized enzyme-reactors for on-line peptide mapping and inhibitor screening.

Keywords: Trypsin reactor; Dextran hydrogel; Surface plasmon resonance; Liquid chromatography; On-line digestion


Identification of highly polar nitroaromatic compounds in leachate and ground water samples from a TNT-contaminated waste site by LC-MS, LC-NMR, and off-line NMR and MS investigations by Alfred Preiss; Manfred Elend; Susanne Gerling; Edith Berger-Preiss; Klaus Steinbach (pp. 1979-1988).
Leachate and ground water samples from a trinitrotoluene-contaminated waste disposal site near a former ammunitions plant in Stadtallendorf, Germany, were analyzed by liquid chromatography (LC)-mass spectrometry (MS) and LC-NMR hyphenated techniques to comprehensively characterize the range of highly polar nitroaromatic compounds. Wherever unknown components could not be identified by comparison with a multistandard, the spectroscopic data obtained on-line were used to make initial structure proposals, which were later confirmed by comparison with authentic reference materials. In those cases where reference materials were not commercially available, unknown compounds were isolated by HPLC cuts and their structures were elucidated by off-line NMR and MS investigations. A variety of previously unknown compounds, including nitrophenols, nitrobenzyl alcohols, methylnitrobenzoic acids, and hydroxynitrobenzoic acids, could be identified. The NMR and MS data are presented here. The main polar compounds were additionally quantified.

Keywords: TNT-contaminated waste site; Polar nitroaromatic compounds; Spectroscopic data


Direct determination of carnosic acid in a new active packaging based on natural extract of rosemary by K. Bentayeb; C. Rubio; R. Batlle; C. Nerín (pp. 1989-1996).
A new antioxidant film is being developed that incorporates a natural extract of rosemary and is intended for contact with food. The rosemary extract has been screened and carnosic acid and carnosol have been determined as the major antioxidant components (6.96% and 0.88%, respectively) that are responsible for the antioxidant properties of the whole extract. Thus, a fast method for the direct determination of carnosic acid in the packaging material, in order to evaluate the antioxidant capacity of the new active plastic, has been developed and optimized. The method consists of extraction from the plastic with methanol, followed by anion exchange solid-phase extraction and final analysis by UPLC–MS. Using this process, the recovery of carnosic acid is about 99%. The complete analytical performance of the method developed here is also assessed. The analytical features of the method, such as the relative standard deviation, reproducibility, repeatability, linear range, and detection and quantification limits, are shown. This method can be subsequently modified to monitor other active components in different packages, and it constitutes a crucial step forward in research into new and improved commercial antioxidant packages.

Keywords: Antioxidant packaging; Rosemary extract; Carnosic acid; Anion-exchange solid-phase extraction; UPLC–ESI–MS


Determination of tetrodotoxin and its analogs in the puffer fish Takifugu oblongus from Bangladesh by hydrophilic interaction chromatography and mass-spectrometric detection by Marc Diener; Bernd Christian; M. Sagir Ahmed; Bernd Luckas (pp. 1997-2002).
Tetrodotoxin (TTX) and its analogs (TTXs), widely distributed among marine as well as terrestrial animals, induce dangerous intoxications. These highly potential toxins are also known as the causative agent of puffer fish poisoning. A newly developed highly sensitive method for determination of TTXs based on hydrophilic interaction chromatography and mass-spectrometric detection is presented. TTX, anhydrotetrodotoxin, 11-deoxytetrodotoxin and trideoxytetrodotoxin were determined in separated tissues of Bangladeshi marine puffers, Takifugu oblongus. TTX was predominant in skin, muscle and liver, whereas trideoxytetrodotoxin preponderated in the ovary. The toxicity of the various tissues was determined by a mouse bioassay.

Keywords: Hydrophilic interaction chromatography; Liquid chromatography–tandem mass spectrometry; Takifugu oblongus ; Tetrodotoxin; Zwitterionic hydrophilic interaction chromatography column


Determination of impurities in magnesium niobate by slurry introduction axially viewed inductively coupled plasma optical emission spectrometry by Dongmei Wu; Haiyun Qu; Min Dong; Anbao Wang; Pingang He; Yuzhi Fang (pp. 2003-2008).
A simple preparation scheme is described for the quantitative analysis of a magnesium niobate sample using slurry introduction axially viewed inductively coupled plasma optical emission spectrometry. Relationships between the stability of slurries and the conditions, such as particle size, pH, dispersant and amount of dispersant, were investigated experimentally. The MgNb2O6 slurry sample was prepared by adding the dispersant sodium polyacrylate and agitation in an ultrasonic bath to ensure good dispersion. Under optimization of pH and amount of dispersant, an analysis of minor and trace impurities (Ba, Ca, Cr, Cu, Fe, Mn, Ni, Pb) in magnesium niobate was accomplished. Applying a paired t test, we showed that the results were in agreement at a 95% confidence level with the reference values obtained by a fusion method for a magnesium niobate sample, which verified that the calibration curves could be established by aqueous standards. Analytical results demonstrate that the factors that affected the accuracy of determination for MgNb2O6 are mainly the particle size of the sample and the stability of slurry.

Keywords: Inductively coupled plasma optical emission spectrometry; Slurry nebulization; Magnesium niobate


Determination of ascorbic acid in pharmaceutical dosage forms and urine by means of an oscillatory reaction system using the pulse perturbation technique by Nataša Pejić; Slavica Blagojević; Slobodan Anić; Ljiljana Kolar-Anić (pp. 2009-2017).
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed.

Keywords: Determination of ascorbic acid; Perturbation technique; Bray-Liebhafsky oscillatory reaction; Pharmaceutical dosage forms; Urine


Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals, plasma and urine by V. K. Gupta; A. K. Singh; Barkha Gupta (pp. 2019-2028).
Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug–tetraphenyl borate (TPB) or drug–phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10−7 M. Calibration graphs were linear over the ranges 5.2 × 10−7–1.0 × 10−3, 1.5 × 10−6–1.0 × 10−3, and 2.6 × 10−7–1.0 × 10−3 M for drug–TPB and 5.8 × 10−7–1.0 × 10−3, 1.8 × 10−7–1.0 × 10−3, and 6.6 × 10−7–1.0 × 10−3 M for drug–PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student’s t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects. Figure Structure of lamotrigine, felbanate and primidone

Keywords: Epilepsy; Potentiometry; Membrane electrodes; Antiepileptic drugs; Pharmaceutical analysis


A low perfusion rate microreactor for continuous monitoring of enzyme characteristics: application to glucose oxidase by G. A. Posthuma-Trumpie; K. Venema; W. J. H. van Berkel; J. Korf (pp. 2029-2033).
This report describes a versatile and robust microreactor for bioactive proteins physically immobilized on a polyether sulfone filter. The potential of the reactor is illustrated with glucose oxidase immobilized on a filter with a cut-off value of 30 kDa. A flow-injection system was used to deliver the reactants and the device was linked on-line to an electrochemical detector. The microreactor was used for on-line preparation of apoglucose oxidase in strong acid and its subsequent reactivation with flavin adenine dinucleotide. In addition we describe a miniaturized version of the microreactor used to assess several characteristics of femtomole to attomole amounts of glucose oxidase. A low negative potential over the electrodes was used when ferrocene was the mediator in combination with horseradish peroxidase, ensuring the absence of oxidation of electro-active compounds in biological fluids. A low backpressure at very low flow rates is an advantage, which increases the sensitivity. A variety of further applications of the microreactor are suggested. Figure Preparation of apoGOx and restoration of enzyme activity using a soluton of FAD

Keywords: Apoglucose oxidase; Deflavination; Enzyme reactor; Flavin adenine dinucleotide; Glucose oxidase
Featured Book
Web Search
Powered by Plone CMS, the Open Source Content Management System

This site conforms to the following standards: