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Analytical and Bioanalytical Chemistry (v.364, #3)
Determination and interpretation of environmental water samples contaminated by uranium mining activities by G. Meinrath; P. Volke; C. Helling; E. G. Dudel; B. J. Merkel (pp. 191-202).
Interpretation of environmental behavior of uranium is based on several steps of data analysis and statistical inference. First step is sampling and analyzing of uranium in field samples by routine laboratory methods. Such methods have to fulfill multiple requirements like robustness, efficiency, low detection limit and precision. A comparison of different approaches in assigning uncertainty to experimentally obtained analytical data shows that classical error estimation is not significantly inferior to more sophisticated modern techniques like inverse regression or orthogonal regression. A second step is the correlation of analytical data with current state of insight into environmental behavior of uranium. Such a correlation furthers the choice of adequate geochemical models and quality of geochemical data base for subsequent detailed analysis, e.g. by geochemical modeling. An appraisal of the individual steps in this complex analysis is given on the basis of statistical procedures for calibration and an EH-pH diagram of uranium for atmospheric conditions.
Computer simulation of the uncertainty of analytical results by O. Mestek; Miloslav Suchánek; Richard Koplík; Hana Fingerová; Eva Čurdová (pp. 203-207).
Uncertainty is an important quality parameter of any analytical result. Estimating the uncertainty of analytical procedures can be rather difficult in many instances. Computer simulation based on multiple repetition of calculation of the resulting quantity while varying slightly the input parameters is an alternative option. The input parameters for the various computation runs are composed of two terms: the constant mean value and the error, obtained as the product of the standard uncertainty of the parameter in question and a random number with the normal distribution N(0.1). This approach can also serve to optimize measuring procedures, as demonstrated on an example of the determination of lead in biological materials by isotope dilution mass spectrometry. The accuracy of the optimized method was tested by analysis of some CRMs, the robustness of the method was examined, and the detection limit (10 ng/g Pb) and repeatability (4 ng/g Pb) were determined.
A possible steady state kinetic model for the atomization process during flame atomic spectrometry: Application to atomization interference effects of aluminum on Group II elements by M. F. Zaranyika; Albert Chirenje (pp. 208-214).
The atomization interference effects of AlCl3 on MgCl2 and CaCl2 during flame atomic absorption spectrometry were studied in terms of a steady state kinetic model which takes into account relative rates of thermal dissociation of analyte and interferant metal salts, recombination of counter atom and analyte and interferant atoms, charge transfer between analyte and interferant species, and ion/electron collisional de-ionization within the plasma. Data are presented showing that the interference of AlCl3 on the atomization of MgCl2 and CaCl2 in an air-acetylene flame is due (a) to interference effects due to AlCl3 which occur prior to complete atomization of the Group II metal chlorides, and (b) to the recombination of the Group II metal and the chlorine atom which is enhanced by the increased density of the chlorine atom as a result of the dissociation of the AlCl3 interferant.
Elucidation of aquatic humic partial structures by multistage ultrafiltration and two-dimensional nuclear magnetic resonance spectrometry by S. Haiber; P. Burba; H. Herzog; J. Lambert (pp. 215-218).
Two-dimensional heteronuclear multiple quantum coherence (HMQC) 1H-NMR was successfully applied to structural investigations of aquatic humic substance (HS) fractions obtained from multistage ultrafiltration (MST-UF) of a selected bog water HS (HO13-XAD8, German Research Program DFG-ROSIG). Details of the HMQC 1H-NMR novel in HS characterization are presented. The results of the combined procedure point out that structural units in isolated HS can be enriched in different mass fractions, for instance fatty acids in the fraction <1kDa, amino acids in the 10–50 kDa fraction and methyl groups attached to quaternary carbon atoms in the high molecular mass fraction >50 kDa.
Determination of the rotational energy barriers of atropisomeric polychlorinated biphenyls by M. T. Harju; Peter Haglund (pp. 219-223).
The rotational energy barriers were determined for twelve of the nineteen environmentally stable atropisomeric polychlorinated biphenyls (PCBs), viz. PCB 84, 131, 132, 135, 136, 144, 149, 174, 175, 176, 183, and 196, by thermal racemization of enantiomerically pure PCBs. The rate of racemization was primarily determined using off-line gas chromatography (GC) or high-performance liquid chromatography (HPLC), with permethylated cyclodextrin (PMCD) as the chiral selector. GC was used for PCB 84, 132, 136, 149, 174, and 176, while PCB 131, 175, and 196 were analyzed using HPLC. The remaining PCBs, i.e. PCB 144 and 183, were separated by HPLC using a Chiralpak OP(+) polymethacrylate column. Gibbs free energy of activation (Δ‡G) was 176.6 to 184.8 kJ/ mole for tri-ortho PCBs. For tetra-ortho PCBs the Δ‡G was estimated to be ∼246 kJ/mole. A buttressing effect of 6.4 kJ/mole was observed for tri-ortho PCBs that have one buttressing chlorine.
Determination of aluminium in AlCl3 and Al2O3 modified silica catalyst supports by M. Nieminen; Lauri Niinistö (pp. 224-227).
X-ray fluorescence spectrometry (XRF) was applied to determine aluminium in AlCl3- and Al2O3-modified silica catalyst supports that were prepared by gas-solid reactions in an atomic layer epitaxy (ALE) process using aluminium chloride or aluminium chloride and water as adsorbates and silica as support. INAA and AAS were used as reference methods to determine the aluminium content of the supports. The calibration of XRF results was done by plotting the Al/Si intensity ratios against the aluminium content as determined by atomic absorption spectrometry (AAS) and verified by instrumental neutron activation analysis (INAA). Correlation factors for the calibration graphs were 0.984 for AlCl3/SiO2 and 0.995 for Al2O3/ SiO2 samples in the aluminium content range 0–2.6 g Al per 100 g of sample.
Optimization by factorial design of focused microwave assisted extraction of polycyclic aromatic hydrocarbons from marine sediment by M. Letellier; H. Budzinski; L. Charrier; S. Capes; A. M. Dorthe (pp. 228-237).
The Focused Microwave (FMW) assisted extraction for organic contaminant analysis, such as polycyclic aromatic hydrocarbons (PAHs), in environmental matrices, was studied and optimized using a factorial design. The effects and interactions of five parameters on the extraction recovery were investigated in a few experiments with a good accuracy: irradiation power and time, volume and nature of solvent, and percentage of moisture of the matrix. The results show that the percentage of water added to the freeze-dried matrix can significantly increase the extraction recovery. The irradiation power has also a positive effect. The choice of solvent is significant: a mixture of heptane/ethanol (80/20, v/v) allows better results than dichloromethane. Some interactions between percentage of moisture and the two previous parameters have been demonstrated: the effect of power and nature of solvent depends on the water content. Some optimal conditions have been established: 10 mL of heptane/ethanol (80/20, v/v), extraction time of 2 min, and different possible pairs of moisture content and irradiation power (140 W and 0% of moisture or 20 W and 40% of moisture) according to the need and wish of the experimentalist; or 10 mL of dichloromethane, extraction time of 2 min, 20 W and 40% of moisture. These optimized conditions provide very good recoveries compared to conventional extraction such as Soxhlet (near 100%) for the model matrix (a marine sediment) used for the factorial design. FMW extraction is a good alternative to Soxhlet extraction with reduction of time and reduction of solvent volume. This study shows that it is possible to substitute chlorinated solvent by a less toxic solvent, like a mixture of heptane and ethanol.
Chemical speciation of heavy metals in soils by use of XAFS spectroscopy and electron microscopical techniques by E. Welter; W. Calmano; S. Mangold; L. Tröger (pp. 238-244).
Pb-contaminated soil samples were investigated using XAFS spectroscopy and SEM/EDX as tools for the analysis of chemical binding forms. The soils originated from the vicinity of a battery factory in Hannover (Germany) and had Pb-contents between 50 g/kg and 140 g/kg. PbCO3, PbSO4, PbO and basic PbCO3 could be identified as the main constituents in the samples by XAFS spectroscopy (EXAFS as well as XANES). This result is consistent with the results of the SEM/EDX investigations on the same soil samples, which showed, that almost all of the lead contained in the soils appears in the form of discrete particles of lead compounds. The EDX analysis of these particles consistently shows the presence of Pb, C, O and S.
Development of a method for the determination of heavy metals in calcified tissues by inductively coupled plasma-mass spectrometry by K. M. Lee; J. Appleton; M. Cooke; K. Sawicka-Kapusta; M. Damek (pp. 245-248).
Calcified tissues are good indicators of exposure to environmental pollution since the mineral phase incorporates heavy metals to which it is exposed during development. Analysis of these specimens is difficult due to the low concentration of the elements of interest compared with the high concentration of the matrix elements. ICP-MS allows rapid multielement determination of samples and a method for the determination of trace elements in calcified tissues is presented with reference to an SRM of Bone Ash (NIST 1400).
Analysis of tetrapyrrolic pigments and derivatives in sediments by high performance liquid chromatography/atmospheric pressure chemical ionization mass spectrometry by Ludovica Verzegnassi; Catherine Riffé-Chalard; Werner Kloeti; F. O. Gülaçar (pp. 249-253).
A new application is described of the on-line high-performance liquid chromatography/positive and negative ion atmospheric pressure chemical ionization mass spectrometry (APCI(+/–)-MS) to the identification of tetrapyrrolic compounds in sediment samples containing complex mixtures of natural pigments and their diagenetic products. The method relies on the production of radical anions in order to determine the molecular masses of the molecules which yield abundant fragment ions when analyzed in the positive mode. This approach allows to verify the occurrence of coeluting components by examining their negative ion spectra and to complete their identification on the basis of their fragment ions produced in the positive ion spectra.
Determination of dihydrozeatin and dihydrozeatin riboside in apples by anodic stripping voltammetry with a carbon fiber microelectrode by Manuel H. Blanco; María del Carmen Quintana; L. Hernández (pp. 254-260).
Analytical methods for determining both dihydrozeatin (DHZ) and dihydrozeatin riboside (DHZR) are optimized via voltammetric anodic stripping using a carbon fiber microelectrode, working in 0.05 M AcH/Ac– buffer pH 4.0, previously accumulated at 0.00 V (vs. Ag/AgCl/ KCl 3 M) for 400 s, at a scan rate of 800 mV · s–1. A detection limit of 40.0 ng · mL–1 and a determination limit of 46.0 ng · mL–1 for the DHZ are obtained. Using the same supporting electrolyte and accumulation potential conditions, but for periods of 70 s and carrying out a stripping scan rate of 900 mV s–1, the detection limit calculated for the DHZR was 14.0 ng · mL–1 and the determination limit obtained was 153 ng · mL–1. The proposed methods were successfully applied to determine minute amounts of cytokinins in apples during their growth period.
Determination of some phytoestrogens in soybeans and their processed products with HPLC and coulometric electrode array detection by Claudia Müllner; G. Sontag (pp. 261-265).
A reliable and sensitive method for quantification of daidzein and genistein by HPLC with coulometric electrode array detection is presented using bisphenol A as internal standard. Acid hydrolysis during extraction of foods allows the quantitative determination of total phytoestrogens as aglycones. The substances are separated on a reversed phase column (Hypersil® Elite C-18), eluted with methanol/acetonitrile/50 mM sodium acetate pH 4.8 (40/ 20/40, v/v/v) and detected in a coulometric electrode array detector using an oxidative detection mode (+390 to +810 mV in increments of 60 mV, vs palladium reference electrode). Phytoestrogen levels from several food items were determined. High levels of daidzein (819 mg/kg) and genistein (960 mg/kg) were found in soy products whereas biochanin A could not be detected in any of these food samples. The recovery depends on the kind of food and was found to be between 72 and 94% for daidzein and genistein.
Determination of citric acid in soft drinks using flow injection with potentiometric detection by José L. F. C. Lima; C. Delerue-Matos; M. Carmo; M. C. V. F. Vaz; Jeanine Silva (pp. 266-269).
A flow injection analysis (FIA) system with potentiometric detection has been developed for the determination of citric acid in commercial fruit juices using a copper-selective tubular electrode. It consists of the complexation of citrate ion with copper (II) ion, monitoring the free copper (II) concentration. Linear relationships between the potential and log concentrations of citric acid in the range of 1 × 10–3 mol/L – 1 × 10–2 mol/L were attained with samples injected in the system without prior treatment. Repeatability was determined by assessing the relative standard deviation for ten replicate injections of different juice samples which varied from 1.2% to 3.0%. The results provided by the automated system were compared with those of an enzymatic conventional method used for the analysis of citric acid in food and a relative deviation of less than 4.0% was found. Recovery trials resulted in values from 97.0% to 101.0%. The system allows a sampling frequency of 60 samples/h.
Liquid-chromatographic determination of sulfadimidine in milk and eggs by N. Furusawa (pp. 270-272).
A method for the determination/identification of residual sulfadimidine (SDD) in milk and eggs by high-performance liquid chromatography (HPLC) with a photo-diode array detector was developed. The sample preparation was performed by shaking with a mixture of 20% (w/v) trichloroacetic acid-methanol (4:1, v/v) followed by ultra-filtration using Molcut II®. A LiChrospher® 100 RP-8 (e) column and a mobile phase of 4% (v/v) acetic acid solution-acetonitrile (6:4, v/v) were used. The average recoveries from spiked SDD samples were 80.8–88.0% with coefficients of variation of 2.8–5.5%. The limits of detection in milk and eggs were 0.01 μg/mL and 0.01 μg/g, respectively. The total time required for the analysis of one sample was less than 20 min.
Study of chemical modifiers for the determination of chromium in biological materials by tungsten coil electrothermal atomic absorption spectrometry by C. G. Bruhn; J. Y. Neira; M. I. Guzmán; M. M. Darder; J. A. Nóbrega (pp. 273-278).
The determination of Cr in digest solutions of mussels and non-fat milk powder by tungsten coil electrothermal atomic absorption spectrophotometry (TC-ETAAS) is affected by interferences. This study reports a critical evaluation of chemical modifiers that could be employed to correct these interferences. The chemical modifiers tested were: Mg [as Mg(NO3)2], Pd [as Pd(NO3)2], NH4NO3, ascorbic acid, and mixtures of these compounds. The less effective modifier was NH4NO3. The best effects, considering thermal stabilization and sensitivity, were obtained in mixtures of ascorbic acid plus Mg. Chromium was determined by TC-ETAAS in certified reference materials of mussels and non-fat milk powder, and results were comparable with those obtained by graphite furnace atomic absorption spectrophotometry (GFAAS).
Spectrofluorometric determination of hesperidin by manual and flow-injection methods by T. Pérez-Ruíz; C. Martínez-Lozano; V. Tomás; J. Fenoll (pp. 279-283).
A reliable and highly sensitive method for the determination of hesperidin is described. It involves the formation of a highly fluorescent complex between hesperidin and aluminium (III) in a micellar medium. There is a linear relationship between fluorescence intensity (λem = 496 nm, λex = 391 nm) and hesperidin concentration over the range 5 × 10–7– 2 × 10–5 mol L–1. The detection limit is 79 μg L–1. The method can easily be adapted to a flow system using a three-channel manifold, the peak height being proportional to the hesperidin concentration over the range 1 × 10–6– 1 × 10–4 mol L–1. Manual and flow-injection procedures have been successfully applied to the determination of hesperidin in orange peel and orange juice.