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Analytical and Bioanalytical Chemistry (v.369, #7-8)
European Analytical Column No. 29 (January 2001)
by Miguel Valcárcel; Ernst-Heiner Korte (pp. 554-555).
Electrochemical methods for monitoring of environmental carcinogens by J. Barek; J. Cvačka; A. Muck; V. Quaiserová; J. Zima (pp. 556-562).
The use of modern electroanalytical techniques, namely differential pulse polarography, differential pulse voltammetry on hanging mercury drop electrode or carbon paste electrode, adsorptive stripping voltammetry and high performance liquid chromatography with electrochemical detection for the determination of trace amounts of carcinogenic N-nitroso compounds, azo compounds, heterocyclic compounds, nitrated polycyclic aromatic hydrocarbons and aromatic and heterocyclic amines is discussed. Scope and limitations of these methods are described and some practical applications based on their combination with liquid-liquid or solid phase extraction are given.
Keywords: Abbreviations AdSV, adsorptive stripping voltammetry; CPE, carbon paste electrode; DME, classical dropping mercury electrode; DPP, differential pulse polarography; DPV, differential pulse voltammetry; eaGCE, electrochemically activated glassy carbon electrode; GCE, glassy carbon electrode; HMDE, hanging mercury drop electrode; HPLC-ED, high performance liquid ¶chromatography with electrochemical detection; LLE, liquid-liquid extraction; LOD, limit of determination; NPAH, nitrated polycyclic aromatic hydrocarbons; SMDE, static mercury drop electrode; SPE, solid phase extraction; TLC, thin layer chromatography
Electrochemical behaviour of sertraline at a hanging mercury drop electrode and its determination in pharmaceutical products by M. H. Vela; M. B. Quinaz Garcia; M. C. B. S. M. Montenegro (pp. 563-566).
The electrochemical behaviour of sertraline at a hanging mercury drop electrode (HMDE) was described. Different voltammetric techniques, such as cyclic, linear sweep, differential pulse and square wave voltammetry, were used. Voltammograms were obtained at different pH values with a Britton-Robinson buffer solution used as supporting electrolyte. The best results were found by square wave voltammetry with electrodeposition at alkaline pH using a borate buffer with a pH = 8.2 for the samples, containing 12% (v/v) methanol. Under optimised conditions, a linear relationship between 2.33 × 10–7 and 3.15 × 10–6 M of sertraline with a limit of detection of 1.98 × 10–7 M was obtained. The electrochemical method developed was applied to the determination of sertraline in pharmaceutical formulations. Recoveries were close to 100%, thus proving efficacy of the proposed method for the quantification of sertraline in commercial samples.
Electrochemical determination of trace amounts of environmentally important dyes by J. Zima; J. Barek; J. C. Moreira; V. Mejstřík; A. G. Fogg (pp. 567-570).
A number of dyes exhibit genotoxic or ecotoxic properties leading to the need for sensitive and selective methods for their determination. Because of the easy reducibility of dyes, modern polarographic and voltammetric methods (differential pulse polarography on classical dropping mercury electrode, differential pulse voltammetry on hanging mercury drop electrode or adsorptive stripping voltammetry) are suitable for the determination of trace amounts of these substances in the general environment in the vicinity of production plants. The scope and limitations of these methods is reviewed and optimum conditions for recently developed methods are summarized. It is shown that the sensitivity of newly developed polarographic and voltammetric methods is sufficient even for the most demanding applications and their selectivity can be increased by their combination with preliminary separation using thin layer chromatography or liquid extraction.
Analytical study of canvas painting collection from the Basilica de la Virgen de los Desamparados using SEM/EDX, FT-IR, GC and electrochemical techniques by M. T. Doménech-Carbó; M. J. Casas-Catalán; A. Doménech-Carbó; R. Mateo-Castro; J. V. Gimeno-Adelantado; F. Bosch-Reig (pp. 571-575).
A new method, based on the combined use of scanning electron microscopy-x-ray microanalysis, Fourier transform infrared spectroscopy, gas chromatography and differential pulse voltammetry, is proposed which permits a parallel investigation of organic and inorganic materials and the characterization of the artistic technique employed in canvas painting. The proposed method has led to analyze succesfully the canvas painting collection exhibited in the Basílica de la Virgen de los Desamparados (Valencia, Spain) which includes art works from 17th to 20th century.
Electrochemical analysis of the alterations in copper pigments using charge transfer coefficient/peak potential diagrams. Application to microsamples of baroque wall paintings attached to polymer film electrodes by A. Doménech-Carbó; M. T. Doménech-Carbó; J. V. Gimeno-Adelantado; F. Bosch-Reig; M. C. Saurí-Peris; M. J. Casas-Catalán (pp. 576-581).
The alteration of copper pigments in art samples was studied by linear scan and cyclic voltammetry using sample-modified Elvacite 2044 film electrodes on the basis of two-dimensional diagrams of charge transfer coefficients calculated from Tafel plots of reductive dissolution processes vs. peak potential. Characteristic voltammetric peaks were obtained for pigments used in the baroque vault frescoes of the Basílica de la Virgen de los Desamparados painted by Antonio Palomino. Results obtained by voltammetric techniques were compared with those from SEM/EDX and FT-IR analysis obtaining a good agreement and leaving to an unambiguous identification of pigments used by Palomino and their alteration products.
Electrochemical monitoring of the thermal decomposition of arenediazonium ions with time in acidic MeOH/H2O mixtures: dediazotization rate constant by R. Pazo-Llorente; C. Bravo-Díaz; E. González-Romero (pp. 582-586).
The rate of the spontaneous decomposition of 4-methylbenzenediazonium tetrafluoroborate, 4MBD, was determined. The effects of solvent composition (MeOH/ H2O) on its electrochemical processes and on those of the derivatized 2-naphthol-6-sulfonate-4-toluene (6S2NPT) azo dye were investigated by Differential Pulse Polarography (DPP). This electrochemical technique shows an effective sensitivity for detecting arenediazonium ions and derivatized azo dyes.
Subspeciation of nickel disulfide by carbon paste electrode voltammetry catalyzed by Ni2+ by John L. Wong; Wenrui Jin; Yanan He (pp. 587-588).
In subspeciation of sulfidic nickel, carbon paste electrode voltammetry was developed for the specific determination of Ni3S2 or NiS, but NiS2 was found to be unreactive. Ni2+ in pH 7.2 acetate solution was able to catalyze NiS2 to undergo redox reactions. The cyclic voltammogram showed two anodic peaks at –0.3 and +0.7 V and a cathodic peak at –0.6 V. The first anodic peak at –0.3 V and the cathodic peak were common among the three nickel sulfides, but the second anodic peak at +0.7 V was unique to NiS2. This peak current gave a linear dose response to NiS2 from 40 to 610 μg, with a correlation coefficient of 0.994, and a detection limit of 40 μg.
Biosensors as new analytical tool for detection of Genetically Modified Organisms (GMOs) by M. Minunni; S. Tombelli; E. Mariotti; M. Mascini; M. Mascini (pp. 589-593).
Three different biosensors for detection of Genetically Modified Organisms (GMOs) are presented. The sensing principle is based on the affinity interaction between nucleic acids: the probe is immobilised on the sensor surface and the target analyte is free in solution. The immobilised probes are specific for most inserted sequences in GMOs: the promoter P35S and the terminator TNOS. Electrochemical methods with screen-printed electrodes, piezoelectric and optical (SPR) transduction principles were applied.
Superoxide dismutase biosensors working in non-aqueous solvent by L. Campanella; S. De Luca; G. Favero; L. Persi; M. Tomassetti (pp. 594-600).
Enzymatic electrodes based on superoxide dismutase enzyme were developed. Using the superoxide dismutase enzyme sensor assembled according to the classical model, poor results were obtained. Results were improved by adopting a new way of assembling the biosensor using a cellulose triacetate layer in which the SOD enzyme is entrapped and sandwiched between two gas-permeable membranes, or using a kappa-carrageenan gel layer entrapping the enzyme, sandwiched between an external gas permeable membrane and an internal cellulose acetate membrane, coupled in each case to the oxygen amperometric transducer. Results obtained by applying the newly developed biosensor to assaying hydrophobic compounds showing radical scavenging properties, operating in dimethylsulfoxide, were also satisfactory.
Influences of non-selective interactions of nucleic acids on response rates of nucleic acid fiber optic biosensors by James H. Watterson; Paul A. E. Piunno; Christopher C. Wust; Sandeep Raha; U. J. Krull (pp. 601-608).
The immobilization of oligonucleotides to solid surfaces can provide a platform of chemistry that is suitable for the development of biosensor and microarray technologies. Experiments were performed using a fiber optic nucleic acid biosensor based on total internal reflection fluorescence to examine the effects of the presence of non-complementary DNA on the detection of hybridization of complementary target DNA. The work has focused on the rates and extent of hybridization in the presence and absence of non-selective adsorption using fluorescein-labeled DNA. A stop-flow system of 137 μL volume permitted rapid introduction and mixing of each sample. Response times measured were on the order of seconds to minutes. Non-selective adsorption of non-complementary oligonucleotides (ncDNA) was found to occur at a significantly faster rate than hybridization of complementary oligomers (cDNA) in all cases. The presence of ncDNA oligonucleotides did not inhibit selective interactions between immobilized DNA and cDNA in solution. The presence of high concentrations of non-complementary genomic DNA had little effect on the extent of hybridization of complementary oligonucleotides, but actually reduced the response times of sensors to cDNA oligonucleotides.
Development of Zn(II) sensors based on the assisted transfer of metal ions by hydrophobic ligands through gel-supported microinterfaces by C. M. Pereira; N. Tirilly; M. C. Martins; F. Silva (pp. 609-612).
Square-wave voltammetry (SWV) has been used to study the transfer of zinc(II) ion under static conditions, assisted by 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (DPT), through gel-supported microinterfaces. Microhole arrays created by laser photoablation of thin polyester films were used to support an organic gel phase prepared by addition of 1,3 : 2,4-dibenzylidenesorbitol (DBS) to a solution of o-nitrophenyloctyl ether (o-NPOE) with the appropriate supporting electrolyte. The results show that SWV can be used with the gel-supported microinterfaces if a gelified aqueous reference is used for the organic phase. Under such conditions a preliminary estimate of the detection limit for the determination of Zn2+ is 5 × 10–8 mol L–1.
Alcohol determination using an acoustic wave sensor by M. Teresa S. R. Gomes; Marta I. S. Veríssimo; João A. B. P. Oliveira (pp. 613-615).
An acoustic wave methodology was developed to quantify alcohols in aqueous solutions. The frequency at minimum impedance of a bare quartz crystal in contact with ethanol solutions was found to be a suitable parameter to quantify ethanol. Ethanol in several Portuguese white wines was analyzed both by the proposed methodology and by the usual areometric method with no statistically significant differences (α = 0.05) in precision or accuracy of the results.
Development of a sensor for calcium based on quartz crystal microbalance by M. Teresa S. R. Gomes; Karina S. Tavares; João A. B. P. Oliveira (pp. 616-619).
A new sensor for calcium based on a piezoelectric quartz crystal is presented. The selectivity depends on the ratio lipophilic salt/ionophore of the composition of the coating of the quartz crystal. A crystal coated with a THF solution of PVC (34.5% w/w), DOS (62.1% w/w) and 10,19-bis[(octadecylcarbamoyl) methoxyacetyl]-1,4,7,13,16-pentaoxa-10,19-diaza cycloheneicosane (3.4% w/w) and a salt/ionophore molar proportion of 60%, corresponding to a frequency decrease of the dry crystal of 6.0 kHz, showed a detection limit to calcium of 2.2 mg/L. Both a standard calcium chloride solution and a commercially balanced salt solution for tissue culture were analyzed subsequent to ion chromatographic separation. The results obtained with the sensor developed were compared with those obtained with a conductivity detector. Although the results from both detectors agreed for the standard solution, only the quartz crystal sensor was able to give reliable results for the tissue culture solution.
Identification of photocatalytic degradation products of non-ionic polyethoxylated surfactants in wastewaters by solid-phase extraction followed by liquid chromatography-mass spectrometric detection by Montserrat Castillo; Gustavo Peñuela; Damià Barceló (pp. 620-628).
The photodegradation of non-ionic surfactants (nonylphenol- and alcohol-polyethoxylates, NPEOx and CnEOx) was investigated in different waters with and without a photoinducter (Fe(III)). Deionized water and industrial effluent spiked at 0.5 mg/L with C10EO6 and NPEO9 were irradiated using a xenon arc lamp. Aliquots of the test solutions were taken at different time intervals and were preconcentrated using solid phase extraction (SPE) with C18 cartridges. Liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was used to identify the chemical species generated from phototransformation of non-ionic surfactants.) and nonylphenol ethoxy acetic acid (NPE2C). Much smaller amounts of degradation products of NPEO9 having only the alkyl chain carboxylated were also formed in the photocatalysis experiment. The identified C10EO6 photoproducts included fatty alcohols and acids. Polyethylene glycols (PEGs) were also formed as the consequence of the central scission of C10EO6 and the deethoxylation of NPEO9. The photodegradation in wastewater samples was more efficient than in deionized water being the half-life (t1/2) of C10EO6, 48 h and 29 h in deionized water and wastewater, respectively, and for NPEO9, 17 h and 14 h in deionized water and wastewater, respectively. When induced photodegradation was undertaken, the t1/2 for NPEO9 was 21 min and 29 min in deionized water and wastewater, respectively. Disappearance of parent compounds was observed after 120 h from the beginning of the photodegradation experiment, or after 210 min of irradiation for the photocatalysis.
Comparison of inductively coupled plasma–atomic emission spectrometry, anodic stripping voltammetry and instrumental neutron-activation analysis for the determination of heavy metals in airborne particulate matter by M. Ochsenkühn-Petropoulou; K.-M. Ochsenkühn (pp. 629-632).
The capability of three analytical techniques, inductively coupled plasma–atomic emission spectrometry (ICP–AES), anodic stripping voltammetry (ASV), and instrumental neutron-activation analysis (INAA) have been compared for the determination of Cd, Fe, Pb, and Zn in airborne particulate matter, collected on cellulose filters, from the atmosphere of the large area of Thessaloniki, Greece. Two procedures were tested for quantitative leaching of these elements from the filters before ICP–AES and ASV, digestion with aqua regia in a Teflon autoclave, after dissolution of the organic matter with HClO4 under ambient conditions, and ultrasonic extraction with a mixture of HNO3 and HCl. Validation of the leaching and digestion procedures revealed that digestion in the autoclave is more effective, especially for Fe. The concentrations of these elements over a decade in both industrial and urban areas of the investigated region are compared.
Separation of organotin compounds by ion-exchange chromatography and their determination by inverse voltammetry by K. M. Ochsenkühn; M. Ochsenkühn-Petropoulou; F. Tsopelas; L. Mendrinos (pp. 633-637).
An ion exchange procedure was developed for the enrichment, separation and quantification of butyltin and phenyltin species, which show very close half wave potentials by their voltammetric determination. As a case study the separation of dibutyltin (DBT) from triphenyltin (TPT) was investigated. Among different ion exchangers tested, the strong acid ion exchanger PUROLITE C100H, used for industrial purposes, was found to be the most suitable. By using a resin bed volume of 25 mL, a flow rate of the feed solution of 1 mL/min and 3 M HCl in methanol as eluent with a flow rate of 0.5 mL/min, a recovery rate of each species of about 80% could be achieved. The detection limit for the determination of DBT and TPT by anodic stripping voltammetry after their separation and enrichment by the above mentioned ion exchange procedure was found to be 0.4 ng/mL for DBT and 6 ng/mL for TPT in the feed solution, respectively. The applicability of the whole procedure was tested on a sediment candidate reference material of BCR (Bureau of Reference Community).
Determination of UV-filters in sunscreens by HPLC by Alberto Chisvert; M.-C. Pascual-Martí; Amparo Salvador (pp. 638-641).
Simultaneous determination of six internationally authorised organic UV-filters in sunscreen formulations was performed by HPLC with UV spectrophotometric detection. The filters determined were: sulisobenzone, oxybenzone, octyl dimethyl PABA, octyl methoxycinnamate, octyl salicylate and homosalate. A C18 stationary phase and a mobile phase of ethanol water acetic acid (70 : 29.5 : 0.5) were used with a flow rate of 0.5 mL/min. UV measurements were carried out at 313 nm. The time required for the analysis was 25 min and the limits of detection were between 0.2 and 2 mg/L, except for sulisobenzone, which gave a limit of detection of 20 mg/L. The procedure proposed provides an accurate, fast and green analytical method, that does not involve toxic organic solvents.
Identification by GC-FID and GC-MS of amino acids, fatty and bile acids in binding media used in works of art by R. Mateo-Castro; J. V. Gimeno-Adelantado; F. Bosch-Reig; A. Doménech-Carbó; M. J. Casas-Catalán; L. Osete-Cortina; J. De la Cruz-Cañizares; M. T. Doménech-Carbó (pp. 642-646).
GC-FID was used as single methodology for the identification and differentiation of proteins, lipids and ox bile from binders used in artistic paintings. The samples were hydrolyzed by HCl. Subsequently, the simultaneous formation of volatile derivatives of the amino, fatty and bile acids with ethyl chloroformate was performed quickly and safely in an aqueous medium. The derivatives were separated by capillary GC and characterized by GC-MS. The ageing of drying oils was studied, identifying pelargonic acid among other degradation products. Proteinaceous and lipoid binding media were characterized by means of the quotients between the areas of the peaks for each amino or fatty acid with respect to the area of the peak for alanine or palmitic acid. Fatty acids from ox bile were easily identified by their retention times characteristic for eicosanoic, docosanoic and pentadecanoic acids. The suggested method was applied to the analysis of binders in baroque paintings by Palomino in Valencia (Spain). Animal gelatine and linseed oil were found.
Development of a SPME-GC-ECD methodology for selected pesticides in must and wine samples by Manuela Correia; Cristina Delerue-Matos; Arminda Alves (pp. 647-651).
A method for the determination of some pesticide residues in must and wine samples was developed using solid-phase microextraction (SPME) and gas chromatography – electron capture detection (GC/ECD). The procedure only needs dilution as sample pre-treatment and is therefore simple, fast and solvent-free. Eight fungicides (vinclozolin, procymidone, iprodione, penconazole, fenarimol, folpet, nuarimol and hexaconazole), one insecticide (chlorpyriphos) and two acaricides (bromopropylate and tetradifon) can be quantified. Good linearity was observed for all the compounds in the range 5–100 μg/L. The reproducibility of the measurements was found acceptable (with RSD’s below 20%). Detection limits of 11 μg/L, on average, are sufficiently below the proposed maximum residue limits (MRL’s) for these compounds in wine. The analytical method was applied to the determination of these compounds in Portuguese must and wine samples from the Demarcated Region of Alentejo, where any residues could be detected.
Ozone measurement with silica cartridges and HRGC-MS analysis by A. Cecinato; V. Di Palo; M. Possanzini (pp. 652-656).
Ozone in ambient air is collected onto silica gel cartridges impregnated with pentafluorophenylhydrazine (PFPH) and 1,2-di(4-pyridyl)ethylene (DPE), so that the pyridine-4 aldehyde formed by DPE oxidation is converted into the corresponding PFPH derivative (PPH). The latter product is determined by HRGC/MS. Since the ozonolysis reaction proceeds stoichiometrically on the cartridge, there is no need for calibration in the gas phase with a standardized ozone source. When compared with UV photometry analyzers, this active chromatographic method (ACM) demonstrates a very good accuracy (ACM/UV photometer = 0.97) and precision (12.0–14.0%) under both laboratory and field sampling conditions at ozone concentrations of 20–200 μg m–3 and exposure times of 1–3 h. The sampling performance was found to be insensitive to relative humidity (r.h.) variations in the 25–90% range and any interference effects could not be observed from various agents, except light, which can be eliminated by using an aluminium shelter. The detection limit for ozone achievable with the ACM in air samples collected at 0.5 L min–1 for 1 h was found better than 0.5 μg m–3.
On-line preconcentration with different solid adsorbents for lead determination by J. B. B. da Silva; S. P. Quináia; M. C. E. Rollemberg (pp. 657-660).
An on-line column preconcentration method based on the combined use of ammonium O,O-diethyldithiophosphate and activated carbon or polyurethane foam as adsorbents has been developed for the determination of Pb in water samples. The complexed Pb was eluted with ethanol and determined by flame atomic absorption spectrometry. The optimum preconcentration conditions are given for each adsorbent. The enrichment factors were 63 and 294, and the detection limits (3σ) 3 μg L–1 and 0.8 μg L–1, respectively, for the carbon and foam systems. When the optimized procedures were applied to the determination of Pb in water samples the recovery efficiency was > 96%.
Comparison of extraction techniques for gas chromatographic determination of volatile carbonyl compounds in alcohols by W. Wardencki; Jaroslaw Orlita; Jacek Namieśnik (pp. 661-665).
Two extraction procedures, i.e. conventional liquid-liquid extraction (LLE) and liquid solid-phase microextraction (SPME) for extraction of the oximes formed after derivatization of carbonyl compounds with o-(2,3, 4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) in alcoholic solutions have been compared. The limit of detection for LLE followed by GC-ECD determination of C1–C6 was in the range of 0.23–3.3 μg/L, whereas for liquid SPME 0.005–0.33 μg/L. Both methods elaborated can be applied to the determination of carbonyl compounds present in spirits and alcoholic beverages.
Determination of cyclodextrins and their derivatives by capillary electrophoresis with indirect UV and conductivity detection by M. Pumera; Ivan Jelínek; Jindřich Jindřich (pp. 666-669).
A fast and simple capillary electrophoretic method suitable for the determination of native α-, β-, γ-cyclodextrins, their randomly substituted tert-butyl derivatives (average degree of substitution 3.8 – 4.4), heptakis (2,6-di-O-methyl)- and heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin was developed. Naphthyl-2-sulfonic acid (2-NSA), 3-iodobenzoic acid (3-IBA) and (1S)-1-phenylethylamine (PHEA) were tested as selective complex forming and UV absorbing background electrolyte additives. The composition of optimized background electrolyte for the separation of uncharged cyclodextrins and their derivatives was: 15 mM 3-iodobenzoic acid titrated with tris[hydroxymethyl]aminomethane to pH 8.0, 5% (v/v) of acetonitrile. A complete resolution of mono-2-O-, mono-3-O- and mono-6-O-carboxymethyl-β-cyclodextrin regioisomers was achieved in the optimized background electrolyte system: 40 mM PHEA titrated with 2-[N-morpholino]ethanesulfonic acid to pH 5.6. In addition to indirect UV detection a contactless conductometric detector was successfully utilized.
Preconcentration and separation of cadmium by use of cobalt(III) hexamethylenedithiocarbamate as a collector prior to its determination by atomic absorption spectrometry by Gorica Pavlovska; Trajče Stafilov; Katarina Čundeva (pp. 670-673).
Co(III) hexamethylenedithiocarbamate has been applied as a collector in colloid flotation preconcentration of Cd from water prior to electrothermal atomic absorption spectrometry (ETAAS). All experimental parameters necessary for successful flotation have been studied and optimized. The ETAAS results were compared with those obtained by inductive coupled plasma-atomic emission spectrometry (ICP–AES). The ETAAS detection limit was found to be 0.003 μg L–1 Cd.
Topochemical investigation of ancient manuscripts by B. Wagner; E. Bulska; A. Hulanicki; M. Heck; H. M. Ortner (pp. 674-679).
Various modern instrumental techniques for surface analysis were applied for the non-destructive physico-chemical examination of works of art. As samples, pieces of ancient manuscripts endangered by iron-gall ink corrosion were used. Surface characterisation of the morphology of the cellulose fibres within corroded and non-corroded parts of the manuscript performed by scanning electron microscopy (SEM) showed seriously damaged cellulose fibres in the written parts. The elemental composition of selected parts of the manuscript was determined by energy dispersive X-ray fluorescence analysis (EDX). A more detailed study of the paper surface was then performed by electron probe microanalysis (EPMA). This technique yields the morphological characteristics of the surface as well as element distribution maps over the written area of the investigated manuscript.
Development of a new flow-through bulk optode for the determination of manganese(II) by C. Sanchez-Pedreño; M. S. García; J. A. Ortuño; M. I. Albero; E. Ballester (pp. 680-683).
A flow-through bulk optode based on the use of 1-(2-pyridylazo)-2-naphthol (PAN) immobilized in a plasticized poly(vinyl chloride) membrane entrapped in a cellulose support, in conjuntion with the flow injection analysis technique, is proposed for the determination of manganese(II). The calibration graph obtained at 570 nm was linear in the range 0.27–27.5 mg L–1 (5 × 10–6– 5 × 10–4 M) Mn(II) with a detection limit of 0.18 mg L–1. The coefficients of variation of the sensor response for 5.5 mg L–1 of Mn(II) were ±0.22% for consecutive measurements (n = 10), ±0.48% between days (n = 5) and ±0.38% between different membranes (n = 6). The sensor was readily regenerated with the carrier acetic acid/acetate buffer of pH 4.5. The method was applied to the determination of manganese in steels, waters and lemon tree leaves.
Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(II) by Alberto Chisvert; A. Salvador; M.-C. Pascual-Martí; Joan G. March (pp. 684-689).
Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LOD are adequate to the analysis requirements. The sample frequency obtained by FI is three-fold higher than that of SI analysis. SI is less reagent-consuming than FI.
Measurement uncertainty of thermodynamic data by Günther Meinrath (pp. 690-697).
Thermodynamic quantities of chemical reactions are commonly derived from experimental data obtained by chemical analysis. The accuracy of the evaluated thermodynamic quantities is limited by the measurement uncertainty of the analytical techniques applied. Straightforward transfer of metrological rules established for determination of single analytes to the more complex process of evaluating values of thermodynamic quantities is not possible. Computer-intensive statistical methods and Monte Carlo techniques are shown to enable integration of existing metrological concepts. An initial stage of the integration of both concepts is presented, taking solubility data for Am(III) in carbonate media as an illustrative example. A cause and effect diagram is created as a means of identification of sources of uncertainty. The uncertainties are used in a resampling-based Monte Carlo study to produce a probability distribution of the value of a quantity.
Interpretation of analytical patterns from the output of chaotic dynamical memories by U. Claußnitzer; S. Quarder; M. Otto (pp. 698-703).
A fundamental study has been carried out to use a nonlinear dynamic system, Freeman’s KIII model, for pattern recognition in analytical chemistry. Filtering of the output of the neuron activity traces in the gamma range has been studied by applying a fast Fourier transform filter. Different possibilities for interpretation of the system output have been investigated. Preliminary results are demonstrated for classification of drugs based on their spectra in the mid infrared range.
Prediction of physical and chemical qualities of crude-oil using statistical time series analysis by B. Dębska; Grzegorz Iwaszek (pp. 704-708).
An application of a statistical time series analysis method is given for the interpretation of physical and chemical qualities of crude-oil samples taken from two oil-fields in Poland. The analytical data was gathered in the years 1995–1999, the information being collected once a month. Randomly selected crude-oil samples were examined in several analytical laboratories. For each sample examined, the following chemical-physical parameters were defined: date, source of the sample, specific gravity, density, colour, relative viscosity, viscosity, kinematic viscosity, drip point, setting point, etc.The data obtained played a decisive role in classifying the samples of crude-oil and in forecasting the properties of crude-oil that will be obtained from the mines in the future. To process the data obtained, the STATISTICA programme was used. It contains a module for time series analysis and for graphical presentation of the results.
An expert system for automated structure elucidation utilizing 1H-1H, 13C-1H and 15N-1H 2D NMR correlations by K. A. Blinov; M. E. Elyashberg; S. G. Molodtsov; A. J. Williams; E. R. Martirosian (pp. 709-714).
A software program for the automated structure elucidation of complex organic molecules using an expert system and utilizing 2D homo- and heteronuclear correlation 1H, 13C and 15N NMR spectroscopy is described. The methodology is illustrated on the basis of the automated structure determination of strychnine and some other examples.
Optimizing analytical methods using sequential response surface methodology. Application to the pararosaniline determination of formaldehyde by J. M. Bosque-Sendra; Stefania Pescarolo; Luis Cuadros-Rodríguez; A. M. García-Campaña; Eva M. Almansa-López (pp. 715-718).
Sequential response surface methodology is a general procedure to re-optimize common analytical methods on the basis of the application of the response surface methodology and of a new approach to the steepest ascent method. This procedure, which is easy to apply, consists of estimating an analytical function relating the response with the experimental parameters by means of a second-degree polynomial. Thus, a 2nd order design covering the total experimental domain is used and when a maximum is obtained, the characteristics of the response surface are confirmed using a new design, which is obtained contracting the first one. In the proposed methodology, Box-Behnken designs are used because they offer advantages in comparison with second order designs more frequently used in the steepest ascent method (central composite designs), i.e. fewer experiments are needed, they are more efficient, they can be moved through the experimental domain and they can even be easily contracted or expanded.
Partial multifactorial design in modelling of UV-spectrometric assays of ascorbic acid with nitrosobenzene and p-nitro-nitrosobenzene by S. Uršić; S. Luterotti; D. Ljubas (pp. 719-726).
Two new reagents, nitrosobenzene (PhNO) and p-nitro-nitrosobenzene (p-NO2-PhNO), have been studied for the analysis of ascorbic acid (AA) by its hypochromic effect on the reagents. The partial multifactorial design of experiments coupled with analysis of parallelism of calibration lines was used to optimize the experimental conditions and evaluate the parameters which affect the sensitivity and accuracy. Two levels at which variable parameters are to be examined should be chosen carefully if a single-step examination is expected to be sufficient. If any parameter roughly influences the system it results not only in severe rotational and translational effects, but also in false results and low selectivity of the approach. In such a case a second step of examination is necessary.The optimization procedures indicated that both PhNO and p-NO2-PhNO are advantageous analytical reagents for the UV-spectrometric assay of AA at pH 3 when measuring the decrease of the absorbance of the reagent peak as analytical signal after 10 and 1 min, resp. After proper modelling both systems were sufficiently robust to be successfully applied for accurate, selective, sensitive, precise and simple analyses of AA even in pharmaceutical preparations with acetylsalicylic acid. Respective analytical performances characterizing AA-PhNO and AA-p-NO2-PhNO systems were: linearity range 2–100 and 2– 70 μmol L–1, CS 0.0094 and 0.0115 L μmol–1, accuracy 101.5 and 98.0%, LOQ 1.3–2.1 and 3.1–3.6 μmol L–1 and RSD 1.3–3.5 and 1.9–3.8%.
Factor analytical study on water quality in Lake Saimaa, Finland by Satu-Pia Reinikainen; Pertti Laine; Pentti Minkkinen; Pentti Paatero (pp. 727-732).
Multivariate data analysis methods (4-way Candecomp-PARAFAC model solved with Multilinear Engine (ME-1)) were used to interpret the data of over two decades to study the changes in the water of Lake Saimaa in Finland. Earlier studies have shown that it is difficult to extract the natural background from the other sources of variation. By using the multilinear model three interpretable factors representing natural and anthropogenic processes could be extracted. The natural long-term variation, seasonal fluctuation and dilution of discharges in the recipient area could be extracted into their own factors, which could be easily visualized. The variation could be also presented with estimated variation in the water quality parameters caused by each of these natural or anthropogenic processes.
Micro-heterogeneity study of trace elements in BCR CRM 680 by means of synchrotron micro-XRF by L. Kempenaers; C. De Koster; W. Van Borm; K. Janssens (pp. 733-737).
BCR CRM 680 is a newly released reference material (RM) with a polyolefinic matrix, doped with various metallic compounds in trace concentrations, to be used for calibration of multi-element trace analytical methods. The micro-heterogeneity of this new CRM was investigated to evaluate the suitability as a RM for trace-level micro analytical techniques. Synchrotron μ-XRF, a trace-level micro analytical method, allows to quantitatively measure the degree of heterogeneity of inorganic trace constituents in solid materials with a homogeneous matrix. The procedure for calculating the minimal sampling mass for homogeneous measurements was employed for BCR CRM 680. By repeating the entire procedure on several samples of the same material, the repeatability of the micro-heterogeneity characterization based on μ-XRF was investigated. Afterwards, the micro-heterogeneity results from the BCR CRM 680 material were used to evaluate the suitability of the micro-heterogeneity procedure by means of a Monte Carlo simulation model. Also the existence of nuggets in the polymer material is looked into.
Teaching the integrated and modern perspectives of analytical chemistry by M. Otto (pp. 738-740).
The present situation of analytical chemistry teaching within a chemistry curriculum is exemplified by the reformed chemistry curriculum in Germany. This approach is contrasted with teaching analytical chemistry within a novel curriculum in natural sciences termed ‘applied science’. The latter curriculum ensures a superior education in chemistry, physics, biology, mathematics and information science, thus gaining an integrated perspective of analytical chemistry.
The proof of analytical chemical education lies in proficiency testing: A proficiency testing programme in polytechnic academia and vocational colleges in The Netherlands by Bauke te Nijenhuis; Karin Heutinck; Ben (B. C.) van Schijndel (pp. 741-743).
Participation in proficiency testing schemes (PT-schemes) is an important way to prove and to improve the skills of analytical chemical students. It gives valuable information on the professional capabilities of the students and is thus an important step in the training of laboratory engineers and technicians. In the programme described three types of samples are offered to the students: chemical, environmental and clinical samples. A guiding protocol presents instructions to the participating student groups. Standard operating procedures are available, but the students are also free to select their own method. The results are methodologically and statistically judged by professional PT-organisers and are presented in the customary way: the dataset, the mean (consensus) value of all participants and the Z-scores. The final presentation of the results takes place in an annual symposium where awards are presented to the best performing student groups, and a lecture programme is presented with subjects in the area of quality assurance and quality control. A selection of results from the KILO/PT/1998–1999 and the KILO/PT/1999–2000 programme is presented.