Analytica Chimica Acta (v.412, #1-2)
Quantitative aspects of brain microdialysis by Jennifer L. Peters; Hua Yang; Adrian C. Michael (1-12).
The concentration difference method of microdialysis has been widely used for quantification of neurotransmitter concentrations in the extracellular space of the mammalian brain. This Critical Review examines the underlying theoretical basis of the method and shows that the validity of the method requires equality of the microdialysis extraction and recovery ratios of the substance under investigation. Experimental evidence that the extraction and recovery ratios of the neurotransmitter, dopamine, are not equal during microdialysis experiments in the brain of living animals is presented. This evidence leads to the conclusion that the no-net-flux concentration of dopamine is not a quantitative measure of the concentration of this important neurotransmitter in the extracellular space of brain tissue. Hopefully, this information will stimulate further research efforts into the quantitative aspects of chemical analysis in the brain.
Keywords: Microdialysis; No-net-flux; Dopamine; In vivo; Uptake;
Determination and pharmacokinetic study of unbound cefoxitin in rat blood and brain with on-line microdialysis and microbore liquid chromatography by Tung-Hu Tsai; Tong-Rong Tsai; Yen-Fei Chen; Chieh-Fu Chen (13-18).
Simultaneous microdialysis probes were inserted into the jugular vein/right atrium and the brain striatum of male Sprague–Dawley rats to examine the unbound cefoxitin level in the rat blood and brain after cefoxitin administration (20 mg/kg, i.v.). Dialysates were directly injected to a liquid chromatographic system using an on-line injector. Samples were eluted with a mobile phase containing methanol-100 mM monosodium dihydrogen phosphate (25:75, v/v, pH 5.5). The UV detector wavelength was set at 235 nm. Using the retrograde method, the in vivo microdialytic recoveries of cefoxitin (1 and 5 μg ml−1) were 44.47±1.76 and 39.87±1.83% for the rat blood (n=6), and cefoxitin (50 and 100 ng ml−1) 16.78±3.66 and 14.56±3.13% (n=6) for the rat brain. Intra- and inter-assay accuracy and precision of the analyses were ≤11% in the range 0.05–10 μg ml−1. Pharmacokinetic analysis of results obtained using the microdialysis-chromatographic method indicated that cefoxitin penetrates the blood-brain barrier. The concentration-time plot has shown that the area under the concentration ratio of protein-unbound cefoxitin in rat brain and blood was about 3.7%.
Keywords: Cefoxitin; On-line microdialysis; Blood-brain barrier; Microbore liquid chromatography;
Performance characteristics for flow injection immunoassay using monoclonal antibodies against s-triazine and 2,4-D herbicides by Milan Fránek; Anping Deng; Vladimı́r Kolář (19-27).
A sequential injection instrument (ALITEA, USA) with a photometric and fluorometric detection unit S2000 (Ocean Optics) was employed for the development of flow injection immunoanalysis (FIIA). The monoclonal antibodies against atrazine, simazine and 2,4-D were immobilized on aminopropyl glass particles by means of avidin/biotin system and packed in plexiglass column of 18 μl volume. Assay characteristics for individual antibody-reactors and regeneration effectivities for acid and alkaline solutions are described. An attempt to prepare a functional mixed antibody-reactor has not achieved success since regeneration conditions found for individual reactors were not compatible with one performance protocol.
Keywords: Flow injection immunoassay; Monoclonal antibodies; Immunoreactor; Regeneration; Calibration;
A novel approach of antibody immobilization based on n-butyl amine plasma-polymerized films for immunosensors by Zhaoyang Wu; Yonghong Yan; Guoli Shen; Ruqin Yu (29-35).
A novel method based on plasma-polymerized films (PPFs) is proposed for immobilizing antibodies (antigens) through a polyelectrolyte-mediated layer. The immobilization of goat-anti-IgG antibody, as an example, is investigated. The n-butyl amine PPFs are deposited on the surfaces of quartz crystal microbalance (QCM) with a radio frequency plasma method using n-butyl amine as the precursor, the IR spectrum indicating the existence of amino-groups in the film. After self-assembling a polystyrenesulfonate (PSS) layer on the PPF, the goat-anti-IgG antibody is immobilized in a 0.2 mg ml−1 of antibody immobilizing solution at pH 5.0. The QCM immunosensor can quantitatively determine NH IgG in the range of 0.7–126 μg ml−1. Moreover, the PSS and protein layers can easily be removed simply by shifting the pH, making the immunosensor regenerable.
Keywords: Plasma-polymerized film; Polyelectrolyte; Immobilization; Immunosensor;
Effect of organic solvents on immunoassays of environmental pollutants studied using a piezoelectric biosensor by Jiřı́ Horáček; Petr Skládal (37-45).
The affinity interactions of haptens with corresponding antibodies were studied in the presence of organic solvents. As the model haptens, the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), and 4,4′-dichlorobiphenyl (DCB, belonging to the group of polychlorinated biphenyls) were used. The piezoelectric quartz crystal was used for real-time monitoring of immunoaffinity interactions without any additional labels. Affinity binding reactions were followed in the presence of water/methanol mixtures. Kinetic studies indicated the decrease of the kinetic association equilibrium constants K A and of the measured resonant frequency changes Δf with increasing methanol contents. To evaluate this influence on the determination of haptens, the competitive immunoassays of 2,4-D and DCB were carried out in the presence of 5, 10 and 25% methanol. The influence of solubility of organic solvent in water on the immunochemical reaction between 2,4-D and monoclonal anti-2,4-D antibody was further characterized in the presence of different organic solvents (10% contents in the assay mixture). The parameter log P was used as a measure of hydrophobicity. Higher values of log P resulted in increased affinity reflected by higher values of K A. Finally, the existence of affinity interaction in the pure organic solvent (toluene) was proved. For this purpose, 2,4-D and DCB were modified with polystyrene moiety functioning as a mass label; thus obtained conjugates were allowed to interact with the corresponding immunoglobulins immobilized at the sensing surfaces. The competition of the DCB-polystyrene conjugate and free DCB for the immobilized IgG was observed in toluene.
Keywords: Direct immunosensor; Organic media; Quartz crystal microbalance;
Design and characterization of a radioluminescent temperature sensor by Andrew M. Leach; Radislav A. Potyrailo; Gary M. Hieftje (47-53).
An environmentally sensitive radioluminescent light source is evaluated for use in remote optical-sensing applications. The sensor is composed of an α-particle-emitting radioisotope coupled with a temperature-sensitive phosphor. Radioluminescent emission intensity is monitored as a function of temperature. Due to the high long-term stability of the radioluminescent source, simple data acquisition systems can be employed. Temperature resolution is found to be proportional to integration time, as would be suggested by counting statistics. Resolution of less than 2°C is possible with this sensor. Additionally, temperature sensitivity is found to be equal to or better than that of other optical temperature sensors. The low radioisotope activity of this sensor makes its commercial use feasible.
Keywords: Radioluminescence; Sensor; Temperature; Phosphor;
Biosensor for detection of hypoxanthine based on xanthine oxidase immobilized on chemically modified carbon paste electrode by Shengshui Hu; Cuilin Xu; Jiahui Luo; Jun Luo; Dafu Cui (55-61).
A novel hypoxanthine (Hx) sensor is constructed using a sodium montmorillonite-methyl viologen carbon paste modified electrode. Xanthine oxidase (XO) is immobilized within a polyaniline film on the electrode surface by electropolymerization. The hypoxanthine detection is based on the oxygen consumed due to the enzymatic reaction involving xanthine oxidase. Electrocatalytic reduction of oxygen and the response of the sensor are evaluated using cyclic voltammetry. The response of the sensor is linear in the range of 1 μM–0.4 mM hypoxanthine and the minimum detectable level is 0.8 μM. The sensor can be applied to the determination of hypoxanthine in fish meat, and it is effective for eliminating interferences from coexisting substances in the samples.
Keywords: Biosensor; Modified electrode; Hypoxanthine; Xanthine oxidase;
An electrochemical sensor based on a clay-coated screen-printed electrode for the determination of arbutin by Ying Shih; Jyh-Myng Zen (63-68).
A preanodized clay-coated screen-printed electrode (CCSPE) is used for the determination of arbutin (hydroquinone-β-D-glucopyranoside) in cosmetic bleaching products by square-wave voltammetry. The preanodization process exhibits a marked enhancement in the current response of arbutin at the CCSPE. Compared to the performance at a preanodized SPE, the coating of clay was found to further improve the sensitivity and reproducibility. Under optimized conditions, the linear range for arbutin detection is up to 90 μM (correlation coefficient=0.999) in pH 10.0 ammonium buffer with a detection limit of 0.18 μM (S/N=3). The electrode can be either disposable or reused since renewal provides good reproducible surfaces. Quantitative analysis was performed by standard addition for the arbutin content in commercial available cosmetic bleaching products.
Keywords: Arbutin; Clay; Screen-printed electrode; Cosmetic bleaching products;
Coulometric micro-titrator with a ruthenium dioxide pH-electrode by Carlo Colombo; Thomas Kappes; Peter C Hauser (69-75).
A coulometric diffusional titrator with a ruthenium dioxide pH-sensing electrode for the end-point detection in acid–base titrations is presented. The device was prepared by galvanic deposition of noble metals onto electrodes etched on a copper clad printed circuit board. Five electrodes were employed: three gold electrodes (two actuator and one counter) for the coulometric production of the titrating protons or hydroxide ions, and a RuO2-electrode and Ag/AgCl pseudo-reference electrode pair for the end-point detection. The RuO2-electrode for pH-measurements showed a linear response to the variation of the pH-value in the range from 2 to 12 pH-units and was useable for a period of 3 months. The device was found to yield linear relationships between the analyte concentration and the equivalence time for concentration ranges of acetic acid and ammonia between about 0.1 and 100 mM.
Keywords: Coulometry; Micro-titrator; Ruthenium dioxide pH-electrode;
Copper complexing capacities of freshwaters by adsorptive cathodic stripping voltammetry by Li Jin; Niall J. Gogan (77-88).
Copper complexation in freshwater was investigated by cathodic stripping voltammetry (CSV) with ligand competition using 8-hydroxyquinoline (oxine). Complexing capacity titrations were used to determine concentrations of natural copper complexing ligands and their conditional stability constants. The effect of the adsorption potential on the determination of copper complexation was studied at three potentials of −0.15, −0.7 and −1.1 V. It was found that the detected complexing ligand concentrations decreased from 6.7 to 69.4% when the potential used was more negative than −0.15 V. The decrease was greater at more negative potentials and lower detection windows. Detailed measurements of copper complexation in freshwater were carried out at three detection windows by varying the oxine concentrations from 7.3 to 36.7 μM and confirmed the presence of several complexing ligands. The detected complexing ligand concentrations were found to decrease with increasing detection window, whereas the conditional stability constants were found to increase. These findings confirm that a spectrum of natural complexing ligands exist in freshwater with weaker ligands being determined at lower detection windows and stronger ligands being determined at higher detection windows. A good linear relation was found between log α CuL x and log α Cuox.
Keywords: Copper complexation; Freshwater; CSV; 8-Hydroxyquinoline;
Characterization of the direct electron transfer and bioelectrocatalysis of horseradish peroxidase in DNA film at pyrolytic graphite electrode by Xiaohong Chen; Chuanmin Ruan; Jilie Kong; Jiaqi Deng (89-98).
Direct electron transfer between horseradish peroxidase (HRP) in a DNA film and pyrolytic graphite (PG) electrode was observed at the formal potential of −0.208 V (versus Ag/AgCl (sat. KCl)) involving the FeIII/FeII redox couple. DNA played the role of charge carrier and facilitated the electron transfer between HRP and the PG electrode. The peak current of the redox process increased linearly with scan rate from 0.05 to 2 V/s, which is typical in thin layer electrochemistry. The number of electrons and the average apparent heterogeneous electron transfer rate constant k s involved in the redox reaction were calculated to be 0.94 and 1.130 s−1, respectively. The formal potential dependence on pH with 54 mV per pH indicated a one-proton-transfer coupled with a one-electron-transfer reaction. Scanning electron microscopy (SEM) showed the different morphologies for isolated DNA film and the complex film of HRP and DNA. Visible absorption and reflectance–absorption infrared (RAIR) spectra proved the heme environment of HRP in DNA film to be in its native status. The embedded HRP molecules in DNA film retained the electrocatalytic activity for hydrogen peroxide. The sensitivity of the HRP-DNA-PG biocomposite was 115.6 μA/cm2 for 2.5×10−4 mol/l H2O2. This HRP-DNA film modified PG electrode represented a valid example of mediator-free amperometric biosensors.
Keywords: Horseradish peroxidase; DNA; Direct electron transfer;
Determination of thiopentone sodium in aqueous and biological media by cathodic stripping voltammetry by Azza M.M Ali; Othman A Farghaly; Mahmoud.A Ghandour (99-110).
A simple and more sensitive cathodic stripping voltammetric method is described for the determination of short-anaesthetic drug thiopentone−sodium (TPS). The method is based generally on the formation of a slightly soluble mercury salt of TPS with Hg onto HMDE surface. The reduction current of the formed salt was measured by both linear sweep (LSCSV) and differential pulse cathodic stripping voltammetry (DPCSV). Different variables were studied and optimized. Four-fold enhancement in the current is observed in the presence of trace Mg ion. The role of Mg ion is discussed in a manner that hydroxide species are formed and accelerate the adsorption of the drug. As low as 1×10−8 mol l−1 (2.60 ppb) and 2×10−9 mol l−1 (0.53 ppb) with accumulation time 240 and 300 s, in the absence and in the presence of Mg(II), respectively, have been determined using both techniques, with the relative standard deviation up to 3.5% (n=4). The interferences of some metal ions, ascorbic acid and amino acids were studied. The determination of the drug in pure pharmaceutical dosage form, urine, and human serum samples have been successfully carried out. The results were compared favorably with the official methods.
Keywords: Cathodic stripping voltammetry; Anaesthetic drug thiopentone sodium; Pharmaceutical analysis in human blood serum; Urine;
Development of an interferent free amperometric biosensor for determination of l-lysine in food by S.C. Kelly; P.J. O’Connell; C.K. O’Sullivan; G.G. Guilbault (111-119).
A highly selective, fast responding amperometric biosensor is described, useful for the determination of l-lysine in food. Common electrochemical interferences, like acetoaminophen and ascorbic acid have zero response at +100 mV applied onto a ruthenium/rhodium coated glassy carbon electrode covered with 1,2-diaminobenzene polymer. This novel transducer was coupled with l-lysine α-oxidase purified from Trichoderma viride and at the appropriate pH, classic substrate interferences from l-ornithine, l-arginine and l-phenylalanine are reduced to 3.4, 1.1 and 0.7% of the response to l-lysine (taken as 100%). No other amino acids respond. The sensor is inexpensive to produce, has excellent repeatability and very good reproducibility. Thus, the l-lysine (protein) content of foods can be almost specifically determined following rapid microwave digestion of the product.
Keywords: l-lysine; l-ornithine; Ruthenium; Rhodium; Amperometric biosensor;
Rapid determination of selenium, lead and cadmium in baby food samples using electrothermal atomic absorption spectrometry and slurry atomization by P. Viñas; M. Pardo-Martı́nez; M. Hernández-Córdoba (121-130).
Procedures for the electrothermal atomic absorption spectrometric determination of selenium, cadmium and lead in different types of baby foods using slurried samples are described. Suspensions prepared in a medium containing 0.1% (w/v) Triton X-100, 30% (v/v) concentrated hydrogen peroxide, 1% (v/v) concentrated nitric acid and a matrix modifier (0.5% (w/v) nickel for selenium, 0.2% (w/v) nickel plus 1% (w/v) ammonium dihydrogenphosphate for cadmium and 1% (w/v) ammonium dihydrogenphosphate for lead) were introduced directly into the furnace. The graphite furnace conditions were optimized for each element. Denterium background correction was used. Calibration with aqueous standard solutions was used for selenium and lead determinations, while the standard additions method was used for cadmium determination. The 3σ detection limits were 5.2, 3.4 and 0.4 ng g−1 for selenium, lead and cadmium, respectively. The reliability of the procedures was established by comparing the results obtained with those found for five fish-based baby foods using a previous microwave-oven mineralization stage and by analyzing six biological certified reference materials. The lead concentration was below the detection limit in all the baby foods tested.
Keywords: Electrothermal atomic absorption spectrometry; Slurry sampling; Selenium; Lead; Cadmium; Baby foods;
Analysis of N-methylcarbamates insecticides and some of their main metabolites in urine with liquid chromatography using diode array detection and electrospray mass spectrometry by J.Martı́nez Fernández; P.Parrilla Vázquez; J.L.Martı́nez Vidal (131-139).
Commonly used N-methylcarbamates, i.e., aldicarb and carbofuran and some of their main metabolites as aldicarb sulphoxide and aldicarb sulphone for aldicarb and 3-hydroxycarbofuran for carbofuran were extracted from human urine by off-line solid phase extraction with graphite carbon and subsequently clean up with NH2-modified silica. Analyte fractionation and quantification were performed by liquid chromatography (LC) with UV detection. The recovery efficiencies of the tested compounds yielded more than 81% at the fortification level of 0.05 μg/ml in urine and their relative standard deviations were between 6 and 16%. The detection limits of each compound ranged between 4 and 10 μg/l. This method involves confirmatory analysis by LC–electrospray mass spectrometry (MS) instrumentation equipped with a single quadrupole mass filter. MS data acquisition was performed by time-scheduled selected ion monitoring (SIM) program. Limits of detection giving values between 0.1 and 0.5 μg/l. Urine samples from a pest control operator were analyzed and the analytes were not found.
Keywords: N-methylcarbamates; Pesticides; Urine;
Determination of micelle/water partition coefficients of cosmetic preservatives by A Bianco Prevot; E Pramauro; M Gallarate; M.E Carlotti; G Orio (141-148).
The hydrophobicity of a group of molecules used as preservatives for aqueous cosmetics, containing surfactants in the form of micelles, was evaluated by means of micellar electrokinetic capillary chromatography (MECC). Five different preservatives mixtures were examined, with a composition analogous to that employed in the preservation of cosmetic formulations. Sodium dodecyl sulphate and sodium dodecyl(polyoxyethylene)1–4 sulphate were used as model surfactant and surfactant present in real cosmetic samples, respectively. The appropriate choice of the micellar velocity marker turned out to be a crucial point for the application of the MECC approach.
Keywords: Parabens; MECC; Surfactants; Partition coefficients;
Rapid polymeric surfactant characterization using a novel flow-injection system with dynamic surface tension detection by Keith E Miller; Robert E Synovec (149-160).
Substantial improvements in a dynamic surface tension detector (DSTD) are presented, providing the rapid measurement of the dynamic surface tension of flowing liquids. The dynamic surface tension is determined by measuring a differential pressure across the liquid–air interface of growing drops. A novel calibration procedure is described and implemented. Differential pressure signals from three drops (water, standard, and analyte) are utilized to make the dynamic surface tension measurement, thereby eliminating the need for optical imaging as required by current methods. Furthermore, corrections for drop elongation are not required, since the growing drops are precisely detached by an air burst actuation method in a regime where the surface tension forces significantly dominate gravitational forces. Drops that would fall with a volume of about 10 μl due to gravity, are precisely detached earlier at a volume as low as 1 μl.Two model surfactant systems, sodium dodecyl sulfate (SDS) and polyoxyethylene-20-cetyl ether (Brij® 58), are evaluated to demonstrate the significance of these improvements to the DSTD. Using 0.5–3.0 mM SDS solutions, the precision of the instrument is demonstrated, with a precision of 0.2 dyn/cm routinely obtained. A reproducible method to perform stress-relaxation experiments of surfactant systems, similar to those reported in the literature, is demonstrated using Brij® 58 solutions. Additional characterization of Brij® 58 solutions above the critical micelle concentration (CMC) is presented, providing insight into the impact that micelles have on dynamic surface properties. Finally, combination of a flow-injection system with the DSTD provides information-rich, multi-dimensional data. The smaller drop volume provided by automated drop detachment results in excellent data density for rapid chemical analysis. The flow-injection system with the DSTD provides rapid characterization of polymeric surfactant solutions above the CMC based on diffusional properties of the micelles and on surface active properties of the micelle/monomer system.
Keywords: Dynamic surface tension; Flow injection; Multi-dimensional; Brij® 58; Polymeric surfactants; Micelles;
Selective stopped-flow injection spectrophotometric determination of palladium(II) in hydrogenation and automobile exhaust gas converter catalysts by Aristidis N Anthemidis; Demetrius G Themelis; John A Stratis (161-167).
A stopped-flow injection spectrophotometric method is reported for the determination of palladium(II), using 2,2′-dipyridyl-2-pyridylhydrazone (DPPH) as a colour forming reagent. The absorbance of the Pd(II)-DPPH complex was monitored at 540 nm, at pH≈0.3. The various chemical and physical parameters were optimized and a study of interfering ions was also carried out. The calibration graph has two linear parts, first in the range 0–25 mg l−1 (s r=0.44%, r=0.9999) with a detection limit of c L=0.084 mg l−1 and the second in the range 25–60 mg l−1 (s r=1.6%, r=0.9996). In both cases the sampling rate was 30 injections per hour. The method is very selective because the strongly acidic medium used prevented the formation of complexes of the reagent with other ions. The method was successfully applied to the determination of palladium in hydrogenation and automobile exhaust gas converters catalysts. The relative standard deviation of the mean values and the recovery ranged between 0.6 and 1.6% and 97.0–102.6%, respectively.
Keywords: Palladium; Spectrophotometry; Stopped-flow injection; Hydrogenation and automobile catalysts;
Sequential injection analysis system for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry by N.V. Semenova; F.M. Bauzá de Mirabó; R. Forteza; V. Cerdá (169-175).
A sequential injection analysis system is proposed for total inorganic arsenic determination by hydride generation-atomic fluorescence spectrometry. The sample, a reducing sodium tetrahydroborate solution and a blank solution containing HCl, ascorbic acid and potassium iodide are sequentially aspirated and then dispensed into a gas–liquid separation cell. An Ar flow sweeps the arsine into the flame of an atomic fluorescence spectrometer. An auxiliary H2 flow was necessary to support the flame. Linear calibration graphs were obtained for arsenic concentrations between 2.5 and 50 μg l−1, the detection limit (3σ b/S) being 0.67 μg l−1. The relative standard deviation of the method was 1.8% (n=9) when 0.5 ml of a 20 μg l−1 As standard solution was aspirated. The sample throughput was 33 samples per hour. The proposed method has been validated by means of reference materials and the results obtained were in good agreement with the certified values.
Keywords: Sequential injection analysis; Hydride generation-atomic fluorescence spectrometry; Arsenic;
Estimation of the heteroscedastic noise in large data arrays by Ji-Hong Wang; Philip K Hopke (177-184).
An approach has been developed to estimate the uncertainties in experimental data that follows a heteroscedastic model. The method presented is based on a hypothesis that the size of data is sufficiently large such that the data values over a limited domain have approximately homoscedastic variance. The implementation of the procedure has two steps. The first step is to estimate an approximate error for each data element. The second step is to estimate the standard deviation for the data points using the errors estimated for the neighboring data. The related mathematical theory is presented, and several simulated data examples are used to illustrate this approach.
Keywords: Heteroscedastic model; Homoscedastic variance; Chemometric methods; Positive matrix factorization;
Voltammetric determination of butylated hydroxyanisole, butylated hydroxytoluene, propyl gallate and tert-butylhydroquinone by use of chemometric approaches by Yongnian Ni; Li Wang; Serge Kokot (185-193).
The voltammetric behavior of synthetic food antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG) and tert-butylhydroquinone (TBHQ), at a glassy carbon electrode in solution of 0.1 mol l−1 perchloric acid containing 1% methanol has been investigated. The obtained linear sweep voltammograms (LSV) showed that all these four compounds have well-defined oxidation waves with peak potentials of 629, 818, 599 and 501 mV for BHA, BHT, PG and TBHQ, respectively. Linear calibration graphs were also obtained in the concentration ranges of 0.5–15.0, 0.5–8.0, 1.0–15.0 and 1.0–15.0 mg l−1 for BHA, BHT, PG and TBHQ, respectively. However, the voltammetric peaks of these antioxidants seriously overlap and it is difficult to determine them individually from a mixture without prior separation. In this work, a method for simultaneous determination of these antioxidants, based on their oxidation at the glassy carbon electrode, with the aid of chemometric approaches, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), has been developed. The method was applied to determine the four antioxidants in a set of synthetic mixtures and several commercial food samples; in general, satisfactory results were obtained.
Keywords: Butylated hydroxyanisole; Butylated hydroxytoluene; Propyl gallate; Tert-butylhydroquinone; Chemometrics; Voltammetry;
Resolution of kinetic system of simultaneous degradations of chlorophyll a and b by PARAFAC by YongXi Tan; Jian-Hui Jiang; Hai-Long Wu; Hui Cui; Ru-Qin Yu (195-202).
A three-way resolution method based on PARAFAC analysis of fluorescence excitation/emission matrices (EEMs) is presented to study the black kinetic system of simultaneous degradations of chlorophyll a and b extracted with other interferents from fresh spinach. The excitation and emission spectral profiles as well as the kinetic concentration profiles of chlorophyll a, b and their degradation products, pheophytin a, b were resolved for this multi-component kinetic system. The degradation of chlorophyll to pheophytin under the optimized experimental conditions is confirmed to follow the first-order reaction model. The most obvious advantage of this method is that the complex black multi-component kinetic system can be resolved and studied in the presence of unknown interferents by applying PARAFAC, which is capable of resolving the three-way data array provided by EEMs and giving a unique solution to the analytical problem.
Keywords: Black system; Chlorophyll degradation; Kinetics; PARAFAC; Pheophytin; Three-way resolution; Trilinear model;
Non-destructive analysis of small irregularly shaped homogenous samples by X-ray fluorescence spectrometry by M. Bos; J.A.M. Vrielink; W.E. van der Linden (203-211).
A new calibration procedure is proposed for the non-destructive analysis of small sized samples of irregular shape by X-ray fluorescence spectrometry. The calibration is performed using normal calibration standards and measurements. The calculations for the calibration and the analysis of unknown samples are based on small modifications of existing procedures and software. The method was tested on fused bead samples as well as on pressed powder samples.The possibility to perform quantitative analysis on this type of samples is obtained at the cost of some accuracy. A relative root mean square error of 1.5% averaged over all elements tested was found in the new calibration procedure for the fused bead samples, versus 1.4% using the normal calibration procedure. For most elements the accuracy deteriorates somewhat except for sodium and magnesium.For the pressed powder samples the relative root mean square errors of the normal and newly proposed calibration method are comparable (average 3%), except for sodium, where there is an improvement from 15 to 7%.
Keywords: Non-destructive analysis; WD-X-ray fluorescence; Irregularly shaped samples;
Scheme for collinear ionization in supersonic jet/multiphoton ionization/time-of-flight mass spectrometry by Takayuki Onoda; Genta Saito; Totaro Imasaka (213-219).
A new ionization scheme is proposed, in which the analyte molecule, ejected from a nozzle into a throat, is expanded from a repeller into a vacuum and immediately ionized and accelerated downstream for time-of-flight mass analysis. The ionization efficiency is improved by a factor of 50, which is in reasonably good agreement with the predicted value of 25, calculated from the distance between the nozzle and the ionization region for the cases of collinear (10 mm) and non-collinear (perpendicular) (50 mm) configurations. This approach has the unique capability for ‘temperature tuning’ of the analyte molecule by changing the position of the ionization region, thus permitting control of the spectral linewidth and, thereby, application of supersonic jet spectrometry to samples of unknown composition.
Keywords: Collinear ionization; Supersonic jet spectrometry; Time-of-flight mass spectrometry; Chlorobenzene;
A new fluorescent probe for sensitive detection of carbonyl compounds: sensitivity improvement and application to environmental water samples by Stéphan Houdier; Sébastien Perrier; Eric Defrancq; Michel Legrand (221-233).
The use of 2-aminooxy-N-[3-(5-dimethylamino-naphtalene-1-sulfonylamino)-propyl]-acetamide (dansylacetamidooxyamine, DNSAOA, 2) as a new molecular probe for trace measurement of carbonyl compounds (i.e. aldehydes and ketones) in water samples is reported. 2 can be considered as an evolution of the parent N-(5-dimethylamino-1-naphtalenesulphonamido)-3-oxopentane-1,5-dioxyamine (dansyloxyamine, DNSOA, 1) molecule that was initially proposed in a recent paper. An updated procedure for the synthesis of 2 leading to higher purity of such oxyamino probes and a subsequent better sensitivity of the method was described. The reactivity behaviour of 2 with solutions containing small amounts of formaldehyde, acetaldehyde, propionaldehyde and acetone is also described: even for concentrations less than 1 μM, C1–C3 aldehydes can be fully derivatized within 10 h and only one calibration curve is needed. Longer reaction times are nevertheless required for accurate measurements of the less reactive acetone. Very low limits of detection (LODs), mainly depending on the initial purity of the probe, have been obtained: 10 nM of formaldehyde and 5 nM of the other carbonyls can be detected. The limit of quantification (LOQ) of the method is close to 25 fmol. 2 was used in measuring the carbonyl content of snow, ice and cloud-water samples. The first data concerning acetaldehyde in alpine and polar snow, and a first estimation of acetone in cloud-water droplets are reported here.
Keywords: Dansylacetamidooxyamine (DNSAOA); Carbonyl compounds; Derivatization; Liquid chromatography; Fluorescence spectroscopy; Snow; Ice; Fog-water;
Electrochemiluminescent determination of peroxydisulfate with Cr(bpy)3 3+ in purely aqueous solution by Guobao Xu; Shaojun Dong (235-240).
A novel method for the sensitive and selective determination of peroxydisulfate was proposed. It was based on an electrochemiluminescent method with Cr(bpy)3 3+. The applied potential was set at −0.5 V in Cr(bpy)3 3+ system which was much more positive than those in Ru(bpz)3 2+ and Ru(bpy)3 2+ systems. A linear calibration was obtained over the range of 7–100 μmol l−1 with a correlation coefficient of 0.993. The relative standard deviation was 2% for 10 replicate injections of 0.01 mmol l−1 S2O8 2− solution. The detection limit (S/N=3) was 1 μmol l−1. The method was successfully applied to determination of peroxydisulfate in phase transfer catalysis.
Keywords: Electrochemiluminescence; Cr(bpy)3 3+; S2O8 2−; Aqueous solution; Phase transfer catalysis;
Novel catalytic spectrophotometric procedure for the determination of trace-level aluminium by Ronghuan He; Jianhua Wang (241-245).
A novel catalytic procedure for aluminium(III) was proposed based on Al3+ catalyzed oxidation of gallocyanine by hydrogen peroxide in a hexamethylene tetramine–hydrochloric acid buffer medium. The calibration graph is linear in the range of 0–200 ng ml−1, and the detection limit is 1.2 ng ml−1. Most foreign ions do not interfere with the determination, except for Cr(VI), Cu2+, Fe3+. The interference of Cr(VI) could be eliminated by reduction to Cr(III), and those of Cu2+ and Fe3+ by extraction with dithizone–carbon tetrachloride and cupferron–chloroform solution, respectively. The procedure had been used to the determination of aluminium in human hair, China tea and water samples. The recoveries were 98.6–101.5%, and relative standard deviations (RSD) were 0.8–1.5%, respectively.
Keywords: Catalytic spectrophotometry; Gallocyanine; Aluminium; Determination;