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Analytical and Bioanalytical Chemistry (v.372, #2)
No Title by Chenghong Lei; Ulla Wollenberger; Nikitas Bistolas; Anthony Guiseppi-Elie; Frieder W. Scheller (pp. 235-239).
Nanostructured sodium montmorillonite was prepared via a colloidal chemical approach and deposited onto glassy carbon electrodes (GCE). Subsequently, hemoglobin was spontaneously adsorbed onto the clay membrane-modified electrode. The colloidal clay nanoparticles and the adsorbed protein were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrochemical impedance behavior of the system was studied using a microlithographically fabricated interdigitated microsensor electrode (IME). The interaction of the clay nanoparticles with hemoglobin was investigated by UV-VIS spectroscopy and electrochemical methods. The heme protein adsorbed in this way displayed a well-defined electrode process and the electron transfer was confirmed to originate from its heme site. Furthermore, nitric oxide affects the hemoglobin electrochemistry.
Keywords: Direct electrochemistry Hemoglobin Nitric oxide Nanomaterials Clay
No Title by Matthias Stiene; Ursula Bilitewski (pp. 240-247).
A novel totally screen-printed flow-through cell for immunoanalysis is presented. It contained screen-printed carbonaceous electrodes, which allowed the determination of peroxidase activity through the electrochemical reduction of p-benzoquinone. As different electrode materials differ strongly in their electrochemical properties, electrodes resulting from various screen-printable carbonaceous pastes were characterized using the hydroquinone/p-benzoquinone redox couple. For most of the electrodes, cyclic voltammogram peak separations of between 550 and 670 mV were observed indicating only quasi-reversible electrochemical behavior. This was confirmed by variation of the peak separation with scan rate. Heterogeneous electron transfer rates of ca. 0.5–1×10–3 cm s–1 and electrochemical activation energies of ca. 20 kJ mol–1 were found. These flow-through cells were not only applied to electrochemical peroxidase activity determinations but also, in combination with a separate detector, as affinity reactors. After biotinylation of screen-printed layers, streptavidin and then biotinylated peroxidase could be bound. However, as signals were only 10–20% of those obtained with a column filled with biotinylated glass beads, only the screen-printed electrochemical detector was applied to the detection of antibodies against the African Swine Fever Virus.
Keywords: Screen-printed flow-through electrode Thin layer affinity reactor Electron transfer rate p-Benzoquinone detection African Swine Fever Virus
No Title by Kenji Yokoyama; Satoshi Koide; Yoshihiro Kayanuma (pp. 248-253).
A cyclic voltammetric simulation that can be applied to an electrochemically mediated enzyme reaction involving any substrate and mediator concentration was developed. Concentration polarization of the substrate in the vicinity of an electrode was considered as well as mediator concentration. Reversible electrochemical reaction with one electron followed by an enzyme reaction with two electrons was modeled. The differential equations for the mediator and substrate were solved using digital simulation techniques. The calculated cyclic voltammograms showed prepeaks when there was a low substrate concentration, high mediator concentration, and high enzyme activity. The prepeak was experimentally observed in the case of an enzyme electrode co-immobilized with a redox polymer. The enzyme electrode loaded at high redox polymer and high enzyme content showed a prepeak at low substrate concentration in the cyclic voltammogram.
Keywords: Digital simulation Redox polymer Enzyme electrode Glucose oxidase Ferrocene Prepeak
No Title by Bernhard P. Schaffar (pp. 254-260).
The new electrochemical thick film biosensors from Roche Diagnostics are presented. Following considerations about the principal requirements that biosensors have to fulfil to be useful for diagnostic purposes, the basic design of these thick film biosensors is shown. In this paper, the new generation of biosensors for glucose, lactate and urea are presented, as well as data from a new biosensor for creatinine. All biosensors are designed for multiple use, at minimum 500 samples or 1 week in-use (depending on type of enzyme used), for determinations in undiluted whole blood or plasma, with extra electrodes to compensate for interferences. The sensors are integrated in a disposable cassette requiring 38 µl sample volume. The analytical ranges of the sensors scope well with the normal and pathological concentrations of metabolites in human blood, e.g. for glucose 0.5–40.0 mmol/L. Both biosensors and interference-compensating electrodes are developed to have a cycle time of 90 s maximum. Method comparison diagrams show excellent correlation of results obtained by biosensors compared to results achieved by reference methods. In addition, the possibility of urea and creatinine determinations in diluted urine is presented.
Keywords: Electrochemical thick film biosensors Diagnosis Metabolites Blood Urine
No Title by Doris Rau; Karl Kramer; Bertold Hock (pp. 261-267).
Fab antibody fragments were constructed by subcloning single chain Fv variable regions from the phagemid vector pCANTAB 5E into the expression vector pASK99. The vector was designed for bacterial secretion of Fab fragments and bears coding sequences for murine constant domains including the Strep-tag II at the carboxyl-terminal end of the constant heavy chain domain. The cloning procedure was carried out with the scFv antibodies IPR-7, IPR-53 and IPR-23. The second and third clone originated from the molecular evolution of the s-triazine selective antibody IPR-7. The Fab fragments were expressed under the transcriptional control of the tetA promoter system. Large-scale production benefits from the anhydrotetracycline-inducible system because of the lower costs for the inducer compared to IPTG and the tightly regulated expression of the recombinant antibody fragments. The Strep-tag purification technology facilitates the isolation of Fab fragments from the E. coli periplasm. The characteristics of functionally expressed Fab fragments were determined by employing a BIAcore 2000 system. The KD of the Fab variant IPR-23 (KD=1.12×10–9 M) optimized by molecular evolution was improved by a factor of 24 compared to the Fab IPR-7 (KD=2.73×10–8 M), which was derived from the template scFv antibody IPR-7. The affinity alteration was also reflected in the 22-fold reduction of the IC50 values of the variants Fab IPR-7 (IC50=60.5 µg/L) and Fab IPR-23 (IC50=2.7 µg/L) in the corresponding atrazine ELISA.
Keywords: Binding kinetics Molecular evolution Antibody s-Triazine
No Title by Holger Schulze; Rolf D. Schmid; Till T. Bachmann (pp. 268-272).
The extensive use of pesticides to protect agricultural crops necessitates reliable tools for the detection of residues in food and water, thus ensuring environmental protection and consumer safety. Neuroinhibitors such as organophosphates and carbamates in particular, represent a potential hazard to human health. These compounds are frequently found in food, but conventional methods of analysis are limited as they are either time consuming or not sufficiently sensitive. As a result, a rapid and sensitive biosensor test based on AChE-inhibition was developed. The disposable AChE-biosensor was directly applied in solvent extracts of food samples using isooctane as extraction solvent. A complete assay could be performed in less than 2 h. Recovery rates of 84% were obtained in tests with spiked orange juice samples. Tests in food samples with a lower water content resulted in reduced recovery rates (44% for peach pap baby food). Phosphorothionate insecticides in food could be detected after direct oxidation with N-bromosuccinimide and solvent extraction. The assay displayed a detection limit of 2 µg/kg paraoxon, which was sufficient for the monitoring of maximum residue limits in food according to EU regulations.
Keywords: Insecticides Food Biosensor Acetylcholinesterase inhibition Solvent extraction
No Title by Izumi Kubo (pp. 273-275).
A phosphate-detection system has been developed which uses phosphate-binding protein (PBP) from Escherichia coli. PBP was immobilized on a sheet of nitrocellulose membrane by cross-linking and the membrane potential of the immobilized PBP was measured.. The response time of the system to phosphate was 5 min. The response was selective to phosphate among other anions. Under optimum conditions 0.1–1.5 mmol L–1 phosphate can be determined with this system.
Keywords: Phosphate Potentiometry Phosphate sensor
No Title by Jana Lange; Christine Wittmann (pp. 276-283).
An enzyme sensor array for the simultaneous determination of the three biogenic amines (histamine, tyramine and putrescine) by pattern recognition using an artificial neural network and its application to different food samples is described. A combination of a monoamine oxidase, a tyramine oxidase and a diamine oxidase (with specific activities sufficient for rapid detection) are immobilised each on a separate screen-printed thick-film electrode via transglutaminase and glutaraldehyde to compare these cross-linking reagents with regard to their suitability. To calculate the amount of a specific biogenic amine, the raw data from multichannel software were transferred to a neural network. The sensor array takes 20 min to complete (excluding statistical data analysis) with only one extraction and subsequent neutralisation step required prior to sensor measurement. The lower detection limits with the enzyme sensor were 10 mg/kg for histamine and tyramine, and 5 mg/kg for putrescine with a linear range up to 200 mg/kg for histamine and tyramine and 100 mg/kg for putrescine. The application area of the enzyme sensor array was tested from fish to meat products, sauerkraut, beer, dairy products, wine and further fermented foods and compared with the data of conventional LC analyses (mean correlation coefficient: 0.854).
Keywords: Biogenic amines (histamine, putrescine, tyramine) Enzymes (diamine oxidase, monoamine oxidase, tyramine oxidase) Enzyme sensor Food samples Liquid chromatography (LC) Neural network Pattern recognition
No Title by Ansgar Erlenkötter; Manfred Fobker; Gabriele-Christine Chemnitius (pp. 284-292).
Biosensors for the determination of creatinine have been developed and integrated into a flow-through system. The sensors are based on a screen-printed three electrode transducer with a platinum working electrode. Applying the multi-enzyme sequence of creatininase (CA), creatinase (CI) and sarcosine oxidase (SO) hydrogen peroxide has been detected amperometrically. An optimal enzyme load was found to be 4.4 U/0.28 U/0.20 U (CA/CI/SO) and 0.28 U/0.20 U (CI/SO) per electrode for the creatinine sensor and for the creatine sensor, respectively. Among a variety of polymers Nafion has shown the highest efficiency to exclude interfering substances like ascorbic acid, acetaminophen and uric acid. First determinations of creatinine in dialysate samples obtained during hemodialysis treatments have shown a good correlation to the conventional methods, the Jaffé reaction (y=0.945x+2.8, R=0.9882, n=9) and the enzymatic photometric method (y=0.891x+3.5, R=0.9917, n=9).
Keywords: Amperometry Creatinine Creatine Hemodialysis Screen-printed electrode Biosensor
No Title by Ingrid Coille; Günter Gauglitz; Johan Hoebeke (pp. 293-300).
The determination of binding constants using surface plasmon resonance (SPR) was introduced to optimise a competitive homogeneous fluorescence energy-transfer immunoassay (ETIA) before labelling. Steroids were chosen as model for the detection of three analytes – estrone, estradiol and ethinylestradiol – by taking three polyclonal antibodies (anti estrone-, anti estradiol- and anti estrogen-antibodies) and the corresponding analyte derivatives used for the immunisation. The active concentration of the antibodies was determined before and after labelling. Inhibition curves were recorded using SPR for all possible combinations of analyte, antibody, and analyte derivatives. The experiments revealed that the active antibody concentration can be reduced to 30% whereas the antibody affinity is not affected by the labelling process. Limits of the use of SPR for determination of affinity constants in solution are discussed. All possible ETIA calibration for the quantification of estrone and estradiol was performed. The lower limits of detection for estrone (0.06 µg L–1) and estradiol (0.17 µg L–1) were reached with the anti-estrogen IgG and its derivative
Keywords: Antibodies Surface plasma resonance Immunoassay
No Title by Masayasu Suzuki; Fumihiko Ozawa; Wakako Sugimoto; Shuji Aso (pp. 301-304).
Miniaturized immunosensors based on surface-plasmon resonance (SPR) have been developed by using the sensor recently developed by Texas Instruments. By using this sensor for human immunoglobulin G (IgG) rapid and repetitive measurements could be performed by alternate injection of sample and glycine-HCl buffer. A sensor for human serum albumin (HSA) could also be developed similarly. One difficulty in immunosensor development is dissociation of the strongly bound antigen–antibody complex. A "regenerable" immunosensor has also been developed for this reason.
Keywords: Immunosensor SPR Miniaturization Human IgG Biosensor
No Title by Akimitsu Kugimiya; Toshifumi Takeuchi (pp. 305-307).
Molecularly imprinted polymers for indoleacetic acid were prepared by co-polymerizing N,N-dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate. The dependence of the affinity and selectivity of the imprinted polymers on HEMA content was evaluated chromatographically. The affinity was improved by increasing the HEMA content; the selectivity of the imprinted polymer was best when the HEMA content was approximately 30%, irrespective of monomer content.
Keywords: Molecular imprinting Molecular recognition HEMA Indoleacetic acid
No Title by Frank F. Bier; Frank Kleinjung; Peter M. Schmidt; Frieder W. Scheller (pp. 308-313).
Binding and catalytic activity of the type II restriction endonuclease EcoRI on immobilized DNA has been observed in real time using three different evanescent wave biosensors and two different immobilization techniques. The method gives direct access to the turnover number (k cat ) without the necessity for the determination of any concentration or activity. The combination of different evanescent wave techniques gives access to the catalytic mechanism and allows the determination of the rate limiting step.
Keywords: Biosensor Optical grating coupler DNA Restriction endonuclease EcoRI
No Title by Hiroshi Muramatsu; Jong Kim; Sang Chang (pp. 314-321).
The principle and applications of quartz-crystal sensors based on the three basic concepts for mass, viscosity, and viscoelastic changes are reported. In the general discussion the realization of a resonant frequency–resonant resistance diagram is described in detail. As an example of application to mass sensing, gas sensing with a carbon-coated quartz crystal is reported. Determination of the blood coagulation factor is used as an example of the application to viscosity sensing. As an example of viscoelastic measurement, an ion-exchange polymer-coated quartz crystal is investigated to show that viscoelasticity changes more than mass in the transport process. The possibility of developing new biosensors and chemical sensors is discussed on the basis of these results.
Keywords: Quartz crystal Resonance frequency Resonant resistance Sensor Viscosity
No Title by F. Villatte; H. Schulze; R. Schmid; T. Bachmann (pp. 322-326).
Anatoxin-a(s) is a hazardous toxin released by cyanobacteria during bacterial blooms. A simple and fast method to detect this hazardous compound using a biosensor based on the electrochemical detection of the activity of acetylcholinesterase was developed. Among several acetylcholinesterases, electric eel enzyme was found to be the most sensitive to anatoxin-a(s) and was thus used to build disposable amperometric sensors. The system displayed a detection limit of 1 µg/L anatoxin-a(s). No unspecific effect was noticed with real water samples but spiked toxin was accurately detected. Oxime reactivation was used to discriminate between the toxin and potential insecticides present in the sample.
Keywords: Biosensor Acetylcholinesterase Anatoxin-a(s) Amperometric detection
No Title by Zheng-Hua Song; Shuang Hou (pp. 327-332).
A novel chemiluminescence (CL) flow sensor for the determination of uric acid in human urine and serum has been developed by using controlled-reagent-release technology. The reagents involved in the chemiluminescence (CL) reaction, luminol and periodate, are immobilized on anion-exchange resin packed in a column. After injection of water, chemiluminescence generated by released luminol and periodate in alkaline media is inhibited in presence of uric acid. By measuring the decreased chemiluminescence (CL) intensity the uric acid is sensed. The decreased response is linear in the 5.0–500.0 ng mL–1 range, with a detection limit of 1.8 ng mL–1. The flow sensor showed remarkable operational stability and could be easily reused for over 80 h with sampling frequency of 100 h–1. The proposed sensor was applied to the determination of uric acid in human urine and serum, and monitoring metabolic uric acid in human urine with RSD less than 3.0%.
Keywords: Flow sensor Chemiluminescence Uric acid Urine Serum
No Title by G. Meinrath; S. Lis (pp. 333-340).
The application of cause-and-effect diagrams to the evaluation of thermodynamic data from UV-Vis absorption spectroscopic analysis is demonstrated. The contributions of measurement uncertainty identified from a cause-and-effect diagram are implemented into a Monte Carlo procedure based on the threshold bootstrap computer-assisted target factor analysis (TB CAT). This algorithm aims at an improvement of data comparability and accounts for non-normality, spectral, residual and parameter correlation as well as random noise in target factor analysis. The ISO Type-B measurement uncertainties are included into the process by normally distributed random numbers with specified mean values and dispersions. The TB CAT procedure is illustrated by a flow diagram and a case study of Nd(III) complexation by picolinic acid N-oxide (pic NO) in aqueous solution. Using 12 experimental spectra as input data, the single component spectra and the formation constant lg β ML of the Nd(pic NO)2+ species are obtained together with the respective probability density distributions. The role of the cause-and-effects approach on the further development of chemical thermodynamics is discussed.
Keywords: Computer-assisted target factor analysis Metrology Chemometrics Spectroscopic speciation Chemical thermodynamics
No Title by Matthias Otto; Anke Schirmer; Ute Claußnitzer; Michael Pfeffer (pp. 341-346).
Optimisation of the separation of a synthetic drug mixture by HPLC is performed by changing both continuous variables, i.e. mobile phase composition and temperature, and categorical variables, here the stationary phase. The retention of solutes is described on the basis of a general linear model in which the different columns are modelled by indicator variables. From the solute-specific retention models the global separation optimum is evaluated on the basis of multidimensional window diagrams using relative retentions of all peak pairs as the figure-of-merit.
Keywords: HPLC optimisation Column-switching Categorical variables
No Title by Guillermo López-Cueto; Miren Ostra; Carlos Ubide (pp. 347-351).
A very simple kinetic method is proposed for the resolution of mixtures of acetone and a second component. It is based on the reaction, at constant temperature, between bromine and acetone. This reaction can be regarded, under certain conditions, as pseudo-zero-order on the bromine concentration. To show the possibilities of the method, mixtures of acetone (between 2 and 20×10–4 mol L–1) and either hydroquinone (between 0.4 and 2.2×10–4 mol L–1) or resorcinol (between 0.1 and 0.7×10–4 mol L–1) have been used with the concentration ratios [acetone]:[hydroquinone] ranging between 0.5 and 50 and [acetone]:[resorcinol] ranging between 2.8 and 200. No systematic errors were found to exist (90% confidence level) and random errors were mainly under 5%. The method can be extended to mixtures of acetone and a second component whose reaction with bromine is fast (phenols, aromatic amines, etc.).
Keywords: Kinetic determination Bromination Acetone
No Title by L. Cabalín; D. Romero; C.C. García; J. Baena; J. Laserna (pp. 352-359).
A pulsed Nd:YAG laser operating on the fourth (266 nm) and second (532 nm) harmonics has been used to generate plasmas on the target surface in air at atmospheric pressure. The influence of wavelength on quantitative analysis of 4 minor elements in stainless steel samples (Si, Ti, Nb and Mo) was investigated. Stainless steel samples with different elemental concentrations were prepared and analyzed by laser-induced plasma spectrometry (LIPS). The effect of laser wavelength on analytical figures of merit (calibration curves, correlation coefficients, linear dynamic ranges, analytical precision, and accuracy values) was found to be negligible when internal standardization (an Fe line) and time-resolved laser-induced plasma are employed. For both wavelengths, the calibration curves presented a good linearity and an acceptable linear dynamic range in the concentration interval investigated. For the four elements studied, limits of detection lower than 150 µg g–1 were achieved. To evaluate the influence of wavelength on precision and accuracy, a set of fifteen high-alloyed steel samples from different stages of steelmaking process have been analyzed. Finally, the long-term stability of the analytical measurements for Mo with 532 nm wavelength has been discussed. RSD values were lower than 5.3% for the elements studied.
Keywords: Laser-induced plasma spectrometry (LIPS) Stainless steel Quantitative analysis
No Title by Vivien F. Taylor; Andrew Toms; Henry P. Longerich (pp. 360-365).
The application of open vessel focused microwave acid digestion is described for the preparation of geological and environmental samples for analysis using inductively coupled plasma-mass spectrometry (ICP-MS). The method is compared to conventional closed-vessel high pressure methods which are limited in the use of HF to break down silicates. Open-vessel acid digestion more conveniently enables the use of HF to remove Si from geological and plant samples as volatile SiF4, as well as evaporation-to-dryness and sequential acid addition during the procedure. Rock reference materials (G-2 granite, MRG-1 gabbros, SY-2 syenite, JA-1 andesite, and JB-2 and SRM-688 basalts) and plant reference materials (BCR and IAEA lichens, peach leaves, apple leaves, Durham wheat flour, and pine needles) were digested with results comparable to conventional hotplate digestion. The microwave digestion method gave poor results for granitic samples containing refractory minerals, however fusion was the preferred method of preparation for these samples. Sample preparation time was reduced from several days, using conventional hotplate digestion method, to one hour per sample using our microwave method.
Keywords: Digestion Geological samples Environmental samples Microwave digestion Open-vessel
No Title by Delgado F. Reyes; Fernández J. Romero; Luque M. de Castro (pp. 366-372).
A competitive continuous immunoassay system for the determination of 3,5,6-trichloro-2-pyridinol (TCP), the major degradation product of the insecticide chlorpyrifos, in water is described. The immunoassay system is based on the transient retention of the specific LIB-MC2 monoclonal antibody anti-TCP as a biotinylated derivative using the streptavidin-biotin interaction. The permanent immobilization of streptavidin on controlled-pore-glass provides an adequate active support for the transient retention of the biotinylated monoclonal antibody anti-TCP. In a subsequent step, the immuno-competitive reaction between the biotinylated LIB-MC2 and the TCP/hapten-POD mixture takes place. This competitive assay relies on the determination of the biocatalytic action of peroxidase, retained in the active support, on a derivatization reaction which yields a fluorescent product. The method exhibits a determination range of 0.01–200 µg L–1 of TCP (r2=0.9919, n=9) with a precision, expressed as RSD, lower than 4.2% and a sampling frequency of 3 h–1. The approach has been applied to the determination of TCP in water with recoveries of 89.7–105.6%.
Keywords: 3,5,6-Trichloro-2-pyridinol Chlorpyrifos Insecticides Environ. water Competitive immunoassay
No Title by Catherine Pirard; Jean-François Focant; Edwin De Pauw (pp. 373-381).
The study and extension of a simple automated clean-up method for polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) to a broad range of polychlorinated biphenyls (PCB) is described. The isolation of seven PCDD, ten PCDF, and three coplanar PCB (cPCB) is extended to eight mono-ortho substituted PCB and seven so-called "marker PCB" (Aroclor 1260) for fatty food samples. This enables quantification of 35 compounds – including all congeners with a WHO toxic equivalent factor (TEF) – in a single extraction and single purification step. The chromatographic behaviour of mono-ortho PCB and marker PCB on a variety of adsorbents, including basic alumina, has been studied. Partitioning of analytes through multi-column sequences is described and correlated with their structural and electronic properties, by use of molecular modelling calculations. The fractionation process available with the Power-Prep automated clean-up system enables rapid independent analysis of the different groups of compounds. Gas chromatography with high resolution mass spectrometry (GC–HRMS) is used for the PCDD/F and cPCB fraction and quadrupole ion-storage tandem in time mass spectrometry (GC–QISTMS) for analysis of the remaining PCB. A comparison study was performed on quality-control samples and real fatty food samples to evaluate the robustness of the new strategy compared with a reference method. On the basis of this simultaneous clean-up, a rapid simplified strategy for PCDD/F and selected PCB analysis determination is proposed for fatty food samples.
Keywords: PCB Dioxins Clean-up Partitioning Alumina
No Title by Yong-Lai Feng; Hisatake Narasaki (pp. 382-386).
A method for speciation of organotin compounds in marine sediments by solvent extraction combined with hydride generation gas chromatography-atomic absorption spectrometry has been developed. Sediment samples spiked with tributyltin and triphenyltin chlorides were homogenized in hydrochloric acid. The chlorides were extracted twice into toluene. Recoveries of the organotin compounds from the spiked sediment samples were improved by the addition of 8-quinolinol. Tributyltin and triphenyltin chlorides form ion-associates with 8-quinolinol in aqueous hydrochloric acid. The method was optimized with respect to derivatization reactions and extraction conditions. Interferences from SnII/IV and additional 13 ions were investigated. Recoveries of 84–100% for tributyltin and 86–100% for triphenyltin were achieved using this method. The detection limits obtained for tributyltin and triphenyltin chlorides were 95 and 145 pg, respectively, corresponding to a relative detection limit of 95 and 145 ng kg–1 in the sediment.
Keywords: Speciation Tributyltin and triphenyltin chlorides Sediment Hydride generation GC-AAS 8-Quinolinol
No Title by Tomás Pérez-Ruiz; Carmen Martínez-Lozano; Virginia Tomás; Jesús Martín (pp. 387-390).
A flow-injection–fluorimetric method for the determination of arsanilic acid is proposed. The assay is based on the on-line decomposition of arsanilic acid in the presence of peroxydisulfate on irradiation with UV light. The arsenate generated in the photochemical reaction was reacted with molybdate in dilute nitric acid to form arsenomolybdic acid, which oxidised thiamine to thiochrome. The thiochrome was monitored fluorimetrically at 440 nm with excitation at 375 nm. The calibration graph was linear in the range 0.10–10.8 µg mL–1 with a correlation coefficient of 0.999. The detection limit was 0.01 µg mL–1 and the sample throughput was 55 samples h–1. The applicability of the method was demonstrated by determining arsanilic acid in animal foodstuffs and water.
Keywords: Arsanilic acid Photodecomposition Flow-injection Fluorimetric detection Animal feed analysis
No Title by Jia-Ping Lai; Xian-Feng Cao; Xiu-Ling Wang; Xi-Wen He (pp. 391-396).
Molecularly imprinted microspheres (MIMs) against trimethoprim (TMP), prepared by aqueous micro-suspension polymerization, bound strongly to TMP, by electrostatic and other non-covalent interactions. The effects of pH, kind and ionic strength (I) of buffer on capacity factors (k′) have been discussed in detail. The capacity factors for TMP increased with increasing pH of both acetate and phosphate buffers. The effects of ionic strength on capacity factors were very substantial and the linear relationship between logk′ and logI was described by the equation logk′=0.3162–0.4420logI with R=–0.9995. The results showed that pH 3.5 acetate buffer (0.05 mol L–1) containing 0.1 mol L–1 sodium chloride and a 1:9 ratio of buffer to methanol were the optimum conditions for separation and determination of TMP. The calibration plot of peak area against concentration was linear with R=0.9979.
Keywords: Trimethoprim Molecularly imprinted microspheres Chromatography MIP
No Title by Lei Cao; Weizhi Tian; Bangfa Ni; Pingsheng Wang; Yangmei Zhang (pp. 397-400).
Radiochemical neutron activation analysis (RNAA) has been used for the determination of eight rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu) in two Chinese certified reference materials (CRM), GBW 08503 (wheat powder) and GBW 09101 (human hair). These determinations are important for possible certification of the above mentioned ultra-trace elements, so far not certified. A simple one-step (REE)F3 precipitation was used. Chemical yields were determined for all relevant elements by means of tracer experiments. The two CRM were also analyzed by inductively coupled plasma–mass spectrometry (ICP–MS) to compare the merits and drawbacks of these two major trace analytical techniques for these particular elements. RNAA was proven to be a reliable technique for ultra-trace analysis, especially in the certification of some ultra-trace elements.
Keywords: RNAA Ultra-trace analysis Wheat powder Human hair Rare earth elements
No Title by M. Bononi; I. Commissati; E. Lubian; A. Fossati; F. Tateo (pp. 401-403).
A new HPLC/DAD (Diode Array Detector) method is proposed for the identification of some carotene isomers. The operating conditions adopted permit the resolution of α-carotene, all-trans-β-carotene, 9-cis-β-carotene, 13-cis-β-carotene and 15-cis-β-carotene. Moreover, the chromatographic conditions reported are simplified in respect of those reported up to now. The method is applied to the determination of carotenoids in a dried Dunaliella salina extract, but it could be also applied to other organic matrices such as eggs.
Keywords: HPLC Carotene isomers