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Analytical and Bioanalytical Chemistry (v.369, #2)
Quantification of derivatives of bisphenol A diglycidyl ether (BADGE) and novolac glycidyl ether (NOGE) migrated from can coatings into tuna by HPLC/fluorescence and MS detection by U. Berger; M. Oehme; Line Girardin (pp. 115-123).
A reversed phase high performance liquid chromatographic method combined with fluorescence and mass spectrometric detection in series is presented for the separation and quantification of bisphenol A diglycidyl ether (BADGE) and novolac glycidyl ether (NOGE) derivatives in extracts from food can coatings, tuna and oil. Fifteen samples of tuna cans bought in four European countries were investigated. Atmospheric pressure chemical ionization mass spectrometry in the positive ion mode (APCI(+)-MS) allowed to tentatively identify BADGE and NOGE related compounds originating from reactions of the glycidyl ethers with bisphenols, phenol, butanol, water and hydrochloric acid. Quantification was based on the external standard method and fluorescence detection. Mass fractions up to 3.7 μg/g were found for hydrochlorination products of bisphenol F diglycidyl ether (BFDGE + 2HCl) in tuna. Furthermore, total migration quantities of phenolic ether compounds were estimated. The highest values found were 20 μg/g in tuna and 43 μg/g in the oil phase.
Quantitative resolution of spectroscopic systems using computer-assisted target factor analysis (CAT) by G. Meinrath; S. Lis (pp. 124-133).
Factor analysis (FA) is widely applicable in analytical chemistry. For suitable data structures, the generality of the approach is a strong point of FA. Using target testing procedures, a wealth of specific informations on the components in a chemical system can be extracted without stating a specific model. Target testing, however, is time-consuming and often heuristic. In the following, application of a computer-assisted target factor analysis (CAT) algorithm is described. CAT estimates a rotation matrix that transforms abstract factors into physically meaningful informations by using general constraints, i.e. non-negativity of absorptions and/or concentrations. Thus, the rotation step in factor analysis is automated and allows application of target factor analysis to situations where none or only very limited information on the real factors and their respective contributions is available. Thus, a target testing procedure of guessing physically meaningful factors and iteratively adapting these factors is performed automatically. Nevertheless, CAT is not a black box procedure. The relative importance of different optimization constraints is balanced interactively. CAT can be applied to all situations where factor analysis can be used. CAT is demonstrated using UV-Vis absorption spectra of a Nd(III) polyoxometalate cryptate system and the system U(VI)-CO2-H2O as examples.
Application of plasma gas modulation technique for improvement of the measurement of Mn emission intensity in ICP-AES by K. Kubota; K. Wagatsuma (pp. 134-138).
A phase-sensitive detection technique associated with a digital lock-in amplifier was applied for an improvement of the detection in ICP-AES. The lock-in amplifier works as an extremely narrow band pass filter. It can pick up the modulated signal, which has the same frequency as the reference signal, from any noise and thus it can improve the signal-to-noise ratio. Modulation of the ICP can be performed by mixing small amounts of air to argon as the outer gas cyclically, because the emission intensities of ionic lines are enhanced by using the mixed gas. An electromagnetic valve, which is placed in the outer-gas flow path, causes periodic variation in the air gas in the outer-gas flow, and thus switching the valve on/off can modulate the ICP. By choosing the appropriate conditions, the addition of air gas enhances the emission intensity of ionic lines more than that of the background, thus leading to improved signal-to-background ratios. At the same time the lock-in amplifier further enhances the ionic emissions because it picks up only the modulated part of the signal. By applying the plasma gas flow modulation technique the detection and the determination limits of the Mn II 257.610 nm line are improved in comparison with the conventional method. A change in plasma shape corresponding to the modulation frequency is observed when the ICP is modulated.
Single-use optical sensor for the determination of iron in water and white wines by L. F. Capitán-Vallvey; E. Arroyo; C. Berenguer; M. D. Fernández-Ramos; R. Avidad (pp. 139-144).
A new method, based on the use of a disposable sensor, for the determination of Fe(II) in waters and wines is proposed. The sensor is formed by an inert rectangular strip of polyester (Mylar) and a circular film (6 mm in diameter) adhered on its surface. This film, which contains the required reagents for the fixation of the analyte by means of a complexation reaction, forms the sensing zone of the sensor. When the sensor is introduced in an acidified (pH 2.5) sample solution containing between 4.0 and 300.0 μg/L of Fe(II), a violet-red colour develops in the initially colourless sensing zone. The linear range of the method depends of the equilibration time of the sensor with the sample solution. Thus, when the equilibration time was 5 min, the linear range was 41.0–300.0 μg/L, while for 60 min the range was 4.0– 50.0 μg/L. Detection and quantification limits were 12.0 and 41.0 μg/L, respectively, for an equilibration time of 5 min. The precision of the method, expressed as relative standard deviation of ten samples of 100.0 μg/L of Fe(II), was 4.9%. Interferences produced by other species usually present in waters or wines have been studied. Cu(II) and Co(II) interfered seriously at concentration levels higher than 100.0 and 150.0 μg/L, respectively. The method was applied to the determination of Fe(II) in different types of waters and wines, using atomic absorption spectrometry as a reference method.
Quinoprotein glucose dehydrogenase modified thick-film electrodes for the amperometric detection of phenolic compounds in flow injection analysis by Andreas Rose; Frieder W. Scheller; U. Wollenberger; Dorothea Pfeiffer (pp. 145-152).
The use of thick-film electrodes as basic transducers for highly sensitive amperometric biosensors using PQQ (pyrroloquinoline quinone) dependent glucose dehydrogenase (GDH) with short response times is described. The enzyme is embedded in a polyurethane matrix on top of a platinum based thick film electrode and its ability to reduce oxidized phenolic compounds is exploited. The electrochemical amplification is based on the oxidation of the analyte on the surface of the electrode followed by its enzymatic reduction. Different parameters of the glucose dehydrogenase electrode system using dopamine as a model analyte were optimized, e.g., membrane thickness, pH value, buffer system, flow rate and storage conditions. Using optimized parameters the sensitivity and detection limits for various phenolic compounds were evaluated. The comparison of electrodes from the identical as well as from different batches shows the ability to produce a number of well reproducible sensors showing remarkably small differences with respect to parameters as sensitivity, response times, and measuring range.
Surface-renewable cobalt(II) hexacyanoferrate-modified graphite organosilicate electrode and its electrocatalytic oxidation of thiosulfate by Peng Wang; Yi Yuan; Guoyi Zhu (pp. 153-158).
Cobalt(II) hexacyanoferrate (CoHCF) was deposited on graphite powder by an in situ chemical deposition procedure and then dispersed into methyltrimethoxysilane-derived gels to prepare a surface-renewable CoHCF-modified electrode. The electrochemical behavior of the modified electrode in different supporting electrolyte solutions was characterized by cyclic voltammetry. In addition, square-wave voltammetry was employed to investigate the pNa-dependent electrochemical behavior of the electrode. The CoHCF-modified electrode showed a high electrocatalytic activity toward thiosulfate oxidation and could thus be used as an amperometric thiosulfate sensor.
Discussion of parameters associated with the determination of arsenic by electrothermal atomic absorption spectrometry in slurried environmental samples by Emilia Vassileva; Hervé Baeten; Michel Hoenig (pp. 159-165).
A slurry sampling – fast program procedure has been developed for the determination of arsenic in plants, soils and sediments by electrothermal atomic absorption spectrometry. Efficiencies of various single and mixed modifiers for thermal stabilization of arsenic and for a better removal of the matrix during pyrolysis step were compared. The influence of the slurry concentration, amounts of modifier and parameters of the pyrolysis step on the As integrated absorbance signals have been studied and a comparison between fast and conventional furnace programs was also made. The ultrasonic agitation of the slurry followed by a fast electrothermal program using an Ir/Mg modifier provides the most consistent performance in terms of precision and accuracy. The reliability of the whole procedure has been compared with results obtained after application of a wet digestion method with an HF step and validated by analyzing eleven certified reference materials. Arsenic detection and quantitation limits expressed on dry sample matter were about 30 and 100 μg kg–1, respectively.
Direct ultrasonic agitation for rapid extraction of organic matter from airborne particulate by S. C. Lee; S. C. Zou; K. F. Ho; L. Y. Chan (pp. 166-169).
Direct ultrasonic extraction (DUE) is proposed as simple and rapid sample pretreatment method. This new approach is applied to the extraction of particulate organic matter (POM) from airborne particulate by using dichloromethane (DCM) or DCM/methanol (90/10, v/v) as extractant. The analytical determination was carried out by weighing the extractable POM on an electrobalance. Total recovery for POM could be obtained when the sample was extracted three times with 25–50 mL extractant each for about 5 min at 50 W ultrasonic power. In comparison with conventional Soxhlet extraction, less extraction time (total 15 min only) and solvent consumption(100 mL) were required by DUE. The efficiency of the DUE was similar or even higher than the routine Soxhlet method. Additionally, the new extractor is very simple and easy to use and can accelerate the extraction procedures of organic components from various solid samples.
Determination of lead in fine particulates by slurry sampling electrothermal atomic absorption spectrometry by Jimmy C. Yu; K. F. Ho; S. C. Lee (pp. 170-175).
A simple method for determining lead in fine particulates (PM2.5) by using electrothermal atomic absorption spectrometry (ETAAS) has been developed. Particulates collected on Nuclepore filter by using a dichotomous sampler were suspended in diluted nitric acid after ultrasonic agitation. The dislodging efficiency is nearly 100% after agitation for 5 min. In order to study the suspension behavior of PM2.5 in solvents, a Brookhaven ZetaPlus Particle Size Analyzer was used to determine the particle size distribution and suspension behavior of air particulates in the solvent. The pre-digestion and modification effect of nitric acid would be discussed. Palladium was added as a chemical modifier and the temperature program of ETAAS was changed in order to improve the recovery. The slurry was introduced directly into a graphite tube for atomization. The metal content in the sample was determined by the standard addition method. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling method. It offers a quick and efficient alternative method for heavy metal characterization in fine particulates.
Determination of the pesticide naptalam and its degradation products by positive and negative ion mass spectrometry by A. Ghassempour; Mohammad Reza Arshadi; Feridoun Salek Asghari (pp. 176-183).
N-1-Naphthylphtalamic acid (naptalam) and its degradation products, 1-naphthylamine and N-(1-naphthyl) phthalimide were simultaneously determined in river water by two independent mass spectrometric (MS) methods. These were negative ion MS (NIMS) and programmable temperature vaporizer gas chromatography mass spectrometry (PTV-GC MS) with electron impact ionization (positive ions). Prior to the NIMS analysis, the samples were preconcentrated by solid phase extraction (SPE) of C18 membrane discs. The PTV-GC MS studies were performed without any preconcentration procedure. Selected ion monitoring (SIM) and internal standardization with naphthalene were applied in both methods. The limits of determination (LOD) of NIMS studies were 230, 270 and 260 ng L–1 for naptalam, 1-naphthylamine and N-(1-naphthyl) phthalimide, respectively, with relative standard deviation (RSD) < 1% (n = 5) and of PTV-GC MS 17, 11 and 15 ng L–1 (RSD < 0.7%, n = 5). The LOD, linearity, RSD and time required for these methods are far better than for HPLC analyses.
Dissolution of molybdenum-silicon (-boron) alloys using a mixture of sulfuric, nitric and hydrofluoric acids and a sequential correction method for ICP-AES analysis by Yûetsu Danzaki; Kazuaki Wagatsuma; Tsutomu Syoji; Kyosuke Yoshimi (pp. 184-186).
For the major component analysis of Mo-Si (-B) alloys by ICP-AES, an appropriate dissolution method is necessary. The general procedure using a HNO3-HF mixture cannot be applied for Mo-Si (-B) alloys due to Si volatilization followed by violent reaction and due to MoO2 precipitation in the preparation of a Mo standard solution from metallic Mo. Good results were obtained with a mixture of 10 mL H2SO4, 1 mL HNO3, 2 mL HF and 12 mL H2O for Mo-Si (-B) alloys. The samples were completely dissolved at room temperature without any losses. A sequential correction method is also suggested to correct several errors in ICP-AES analysis such as fluctuation in the emission intensities, spectral interferences, non-spectral interferences and blank values.
Molybdenum determination in iron matrices by ICP-AES after separation and preconcentration using polyurethane foam by Sérgio Luis Costa Ferreira; Hilda Costa dos Santos; Djane Santiago de Jesus (pp. 187-190).
A procedure is proposed for the separation and determination of molybdenum in iron matrices by a batch process. It is based on the solid-phase extraction of the molybdenum(V) ion as thiocyanate complex on polyurethane (PU) foam. The extraction parameters were optimized. Using 0.20 mol L–1 hydrochloric acid, a thiocyanate concentration of 0.10 mol L–1, 100 mg of polyurethane foam and shaking time of 10 min, molybdenum (5–400 μg) can be separated and preconcentrated from large amounts of iron (10 mg). Desorption was carried out instantaneously by conc. nitric acid or acetone. Distribution coefficients, sorption capacity of the PU foam and coefficients of variation were also evaluated. The effect of some ions on the separation procedure was assessed. Iron(III) should be reduced to iron(II). The proposed procedure was used to determine molybdenum in standard iron matrices such as steel and pure iron. The achieved results did not show significant differences with certified values.
Separation of gallium and indium from ores matrix by sorption on Amberlite XAD-2 coated with PAN by P. Bermejo-Barrera; N. Martínez-Alfonso; A. Bermejo-Barrera (pp. 191-194).
A chelating sorbent obtained by adsorption of 1-(2-pyridylazo)-2-naphthol (PAN) on Amberlite XAD-2 was used for the preconcentration of Ga and In. The analytical characteristics of the chelating sorbent were investigated and optimun sorption conditions for these metals under dynamic conditions were established. A peristaltic pump is used to adjust the flow rate of the solution. Elements are collected from the column by using a mixture adjusted to a pH range of 4–7 and 6–12 by ammonia or ammonium chloride for Ga and In, respectively. The procedure developed was applied to the analysis of different ores.
Separation of vanadium, niobium and tantalum as ternary mixed-ligand complexes by capillary electrophoresis using chelation with 4-(2-pyridylazo)resorcinol and tartaric acid by Bi-Feng Liu; Liang-Bin Liu; Hong Chen; Jie-Ke Cheng (pp. 195-197).
Vanadium(V), niobium(V) and tantalum(V) were separated as ternary mixed-ligand complexes by capillary electrophoresis using 4-(2-pyridylazo)resorcinol (PAR) as the color chelating reagent. Four carboxylic acids such as tartaric acid (Tart), oxalic acid, citric acid and acetic acid were investigated as the additional ligand. The first was chosen as the best. Other parameters such as the concentration ratio of Tart to PAR, buffer concentration, injection time and applied voltage were also optimized. Under the optimized conditions, a complete separation of the three metal complexes was accomplished within 10 min. A linear calibration curve in the range of two orders of magnitude was obtained.