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Analytical and Bioanalytical Chemistry (v.367, #3)
Evaluation of nonlinear modeling based on artificial neural networks for the spectrophotometric determination of Pd(II) with CPA-mK by Gang Sun; Xingguo Chen; Qianfeng Li; Huaiwen Wang; Yongyao Zhou; Zhide Hu (pp. 215-219).
A new method is proposed for the spectrophotometric determination of Pd(II), based on the reaction of Pd(II) with 2-(4-chloro-2-phosphonophenylazo)-7-(3-carboxyphenylazo)-1,8-dihydroxynaphthalene-3,6-disulfonic acid(CPA-mK) in sulfuric acid without heating. Beer’s law is obeyed for 1.0–4.0 μg of Pd (II) in 10 mL of solution. The calibration curve from 1.0 to 42.0 μg in 10 mL of solution is modeled successfully by artificial neural networks (ANNs). The maximum relative error between experimental values and the values predicted by ANNs is 1.5%. In comparison with some mathematical functions, ANNs show better ability for curve fitting, thus greatly extending the applicable range of the calibration curve of this new system. The method has been applied to determine Pd (II) in ore and catalyst samples with a relative error of less than 4% and with a recovery range between 94% and 103%.
Mathematical algorithm for qualitative and semiquantitative analysis of petroleum hydrocarbons in solid wastes using on-line gas chromatography by R. Donau; S. Marten; B. Wronski (pp. 220-225).
Non-degradated mineral-oils like gasoline, solvent naphtha, diesel fuel, fuel and lubricating oils provide a characteristic fingerprint gas chromatogram. This visual classification, e.g. in solid wastes, is complicated due to the simultaneous presence of several mineral-oils.Therefore, a mathematical algorithm for the separation of gas chromatographic fingerprint of “single mixtures” of aliphatic hydrocarbons is developed. The technique ¶is essential for analysis of time-overlapping “single mixtures” of petroleum hydrocarbons (so-called “complex mixtures”) and it relies on the concentration-varying hydrocarbons during evaporation.It is possible to separate the data from the gas chromatogram of a “complex mixture” of hydrocarbons into the chromatograms of the pure “single mixtures” and to give their respective concentrations. A synthetic „complex mixture” of kerosene, diesel fuel and lubricating oil is used to illustrate the method.
New low-index liquid refractive index standard: SRM 1922 by J. R. Verkouteren; S. D. Leigh (pp. 226-231).
A new standard for the calibration of refractometers has been developed. Standard Reference Material (SRM) 1922 is a mineral oil with a refractive index n D = 1.46945 at 20 °C, which is within the range of the Brix scale (% sucrose). The change in refractive index with temperature (dn/dT) has been characterized for the range 15 °C to 35 °C to allow for calibrations within that range of temperatures. The refractive indices were measured at 5 wavelengths in the visible spectrum by using the method of minimum deviation with a ± 2–3 × 10–5 uncertainty at 20 °C. The values of n D and dn D/dT were determined by fits of a two-term Cauchy function to the values at the measured wavelengths with a ± 6 × 10–5 uncertainty in n D at 20 °C.
River sediment (S-37) – A new analytical quality control material ensuring comparability of chlorinated hydrocarbon analysis during an international environmental study in China by B. M. Gawlik; D. Martens; B. Henkelmann; K. W. Schramm; A. Kettrup; H. Muntau (pp. 232-240).
A sediment reference material (S-37) was prepared as analytical quality control material to be used within an international project on polychlorinated hydrocarbon analysis in two Chinese rivers. The raw material was sampled during a cruise on Yangtse River and transported afterwards to the JRC Ispra for further processing.The material was treated according to the general principles applicable for candidate reference material production. After a thorough homogeneity study of the bulk the material was bottled. A total of 1080 bottles each containing 50 g of dry sediment powder was obtained. Final homogeneity and stability testing proved the material to be fit for the purpose.Isotope dilution GC/MS was used to establish target values for pentachlorobenzene (1.17 ± 0.08 ng/g), hexachlorobenzene (3.60 ± 0.17 ng/g), octachlorostyrene (0.19 ± 0.01 ng/g), pentachloroanisole (0.52 ± 0.02 ng/g), α-HCH (0.70 ± 0.05 ng/g), β-HCH (1.38 ± 0.18 ng/g), γ-HCH (0.83 ± 038 ng/g), 2,4′-DDT (0.36 ± 0.04 ng/g), 2,4′-DDE (0.29 ± 0.02 ng/g), 2,4′-DDD (0.49 ± 0.02), 4,4′-DDT (3.42 ± 0.47 ng/g), 4,4′-DDD (1.29 ± 0.17 ng/g), PCB 28 (0.11 ± 0.01 ng/g), PCB 52 (0.09 ± 0.003 ng/g), PCB 101 (0.07 ± 0.003 ng/g), PCB 138 (0.06 ± 0.003 ng/g) and PCB 153 (0.06 ± 0.003 ng/g). Furthermore, indicative values for major and minor constituents as well as for polychlorinated dibenzodioxines and -furanes were measured.
Amperometric detection studies of Nafion/indium hexacyanoferrate film for the determination of electroinactive cations in ion chromatography by Q. Xu; S. Zhang; W. Zhang; L. Jin; K. Tanaka; H. Haraguchi; A. Itoh (pp. 241-245).
An amperometric detector based on the chemical modification of Nafion and indium (III) hexacyanoferrate (II, III) thin film (Nafion/In-CN-Fe) onto a glassy carbon (GC) electrode, was first successfully used for the determination of electroinactive cations (Li+, Na+, K+, Rb+, Cs+, NH4 +) in single column ion chromatography (IC). A set of well-defined peaks of electroinactive cations was obtained. The detection limits of the cations are 8.9 × 10–6 mol/L for Li+, 2.3 × 10–6 mol/L for Na+, 5.2 × 10–6 mol/L for K+, 4.8 × 10–6 mol/L for Rb+, 4.0 ׶10–6 mol/L for Cs+ and 5.3 × 10–6 mol/L for NH4 + at a single-to-noise ratio of 3. The proposed method was quick, sensitive and simple. The cations in rainwater and mineral water were successfully analyzed by this method.
Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry by M. Shamsipur; M. H. Mashhadizadeh (pp. 246-249).
A simple and reliable method has been developed to selectively separate and concentrate trace amounts of silver ion from aqueous samples for the subsequent measurement by atomic absorption spectrometry. Ag+ ions are absorbed quantitatively during passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by hexathia-18-crown-6. Almost all matrix elements will pass through the disk to drain. The retained Ag+ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 50 ng Ag+ per 1000 mL. The effects of various cationic interferences on the recovery of silver in binary mixtures were studied. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.
HPLC combined with ICP-MS for the determination of trace amounts of rare earth impurities in high-purity La2O3 by using 2-ethylhexyl hydrogen-2-ethylhexylphosphonate resin as a stationary phase by Shuai Qin; Zucheng Jiang; Bin Hu; Yongchao Qin; Shenghong Hu (pp. 250-253).
A new method for the determination of trace rare earth impurities in high-purity La2O3 by HPLC combined with ICP-MS is proposed. The chromatographic retention behavior of La and Ce in HPLC was studied with 2-ethylhexyl-hydrogen-2-ethylhexylphosphonate (P507) resin as the stationary phase and inorganic acid (HNO3) as the mobile phase. The effects of acidity of the mobile phase, flow rate of eluent and column oven temperature on the separation of La and Ce were investigated in detail. The results of the effect of different ratios of La / Ce showed that a favorable separation of La and Ce could be obtained easily and rapidly with the method presented. Compared with the conventional open column method, the proposed separation system shows a good performance with regard to short separation time, low reagent consumption, and simple operation. The method has been applied to the analysis of real samples of high-purity La2O3 with satisfactory results.
Separation and preconcentration combined with glow discharge atomic emission spectrometry for the determination of rare earth elements (La, Nd, Eu, Dy, Y) in geological samples by W. Huang; B. Hu; H. Xiong; Z. Jiang (pp. 254-258).
A method of glow discharge atomic emission spectroscopy (GD-AES) is described for the determination of rare earth elements (REEs) after separation and preconcentration by micro-column packed with immobilized 1-phenyl-3-methyl-4-benzoyl-5-pyrazone (PMBP) on microcrystalline naphthalene. The graphite electrode with solution residue on its surface was used as a cathode. Various factors (the form of cathode, working condition) influencing the determination of the analytes were studied in detail. Under the experimental conditions selected, the detection limits for the determination of La, Nd, Eu, Dy and Y are 0.24, 0.32, 0.01, 0.07 and 0.06 μg/mL, respectively, with relative standard deviations (RSDs) in the range of 5–10%. The method was applied to determine La, Nd, Eu, Dy and Y in geological samples, and the analytical results are in good agreement with the reference values.
Direct determination of trace rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling by B. Cai; B. Hu; Z. Jiang (pp. 259-263).
A new method for the determination of trace amounts of 14 rare earth elements in high purity Y2O3 using fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry with slurry sampling was developed. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporization of the analytes from graphite furnace. The main factors affecting analytical signals were investigated systematically. The interference of matrix could be minimized in the presence of PTFE. Under optimum conditions, the detection limits for rare earth elements were 0.032 ng∼2.52 ng and the relative standard deviations were in the range of 1.4% to 4.3%. The proposed method was applied to the direct analysis of high purity Y2O3 powder with satisfactory results.
Precise and sensitive determination of nitrite by coulometric backtitration under flow conditions by Z. K. He; B. Fuhrmann; U. Spohn (pp. 264-269).
A novel method performing for coulometric backtitrations in flow channels was developed, which ¶was applied for the precise and sensitive determination of low concentrations of nitrite. Under acid conditions nitrite is reacting stoichiometrically with hydrazine, the remained excess of which is backtitrated with electrogenerated bromine. The titration course is recorded either amperometrically or chemiluminometrically. Hydrazine can be determined precisely and accurately in the range between 0.1 μM and 1 mM without calibration. Nitrite is reduced by hydrazine according to the reaction 2 NO2 – + 2 H+ + NH2-NH2→N2O + N2 + 3 H2O. Applying the amperometric and the chemiluminometric end-point location nitrite was determined accurately and precisely in the ranges 0.25–65 μM and 0.10–50 μM, respectively. The method was applied to the determination of nitrite in tap and river water.
Flow injection spectrophotometric determination of anionic surfactants using methyl orange as chromogenic reagent by Qiaohong He; Hengwu Chen (pp. 270-274).
A flow injection(FI) spectrophotometric method for the determination of anionic surfactants was developed on the basis of the competition for the cationic surfactant cetyl pyridine (CP+) chloride between the acidic dye methyl orange (MO) and anionic surfactants. In a pH 5.0 medium the cation of cetyl pyridine (CP+) reacts with dissociated methyl orange (MO–) to form an ion-associate complex, causing a blue shift of λmax from 465 nm for MO– to 358 nm for the CP+· MO– associate. The MO– in the ion-associate complex can be quantitatively substituted by such anionic surfactants as sodium dodecyl benzene sulfonate (DBS) or sodium lauryl sulfate (LS), leading to an increase in the absorbance measured at 465 nm. This increased absorbance value is proportional to the concentration of anionic surfactants. Various chemical and physical parameters for the FI spectrophotometric method were optimized, and interference-free levels were examined. At the optimized conditions, Beer’s law was obeyed in the range 1.4 ∼ 25 mg/L sodium DBS for an injected sample volume of 180 μL, and a detection limit of ¶0.22 mg/L for sodium DBS was achieved at a sampling rate of 90 h–1. Eleven determinations of a 16 mg/L sodium DBS solution gave a RSD of 0.4%. The proposed method has successfully been applied to the determination of anionic surfactant concentration in waste water and in detergents.
Estimation of unsaturated hydrocarbon pollutants in air based on selective gas chromatography with ozone by T. I. Poznyak (pp. 275-278).
Regular monitoring of toxic organic pollutants in air is a very important issue in environmental pollution control. Among these, unsaturated hydrocarbon pollutants (UHP) such as ethylene and β-propylene and another ¶18 olefins are of prime importance. A very fast method for the individual identification of UHPs in air is proposed. This method is based on gas-chromatographic separation with selective detection of unsaturated organic compounds (UOC) and on the chemical reaction of UOC with ozone in the gas phase. In view of the mathematical model derived for this ozonation process, a comparison of FID-chromatogram and ozonogram can be carried out for identification of the contaminants. This identification can be performed without preliminary separation in the presence of the main components. The method provides a high sensitivity (< 0.005 to 0.72 mass %) and selectivity.
A simplified HPTLC screening method for the estimation of the PAH content in soil samples by H. Kutsch; U. Schoen (pp. 279-283).
Based on a highly significant correlation between the visual fluorescing fraction of PAH on the one hand and the total EPA-PAH16 content in mineral soils on the other hand, a deliberately incomplete RP-TLC separation of these compounds into a few fingerprint-like compressed bands within a determined “PAH window” has been achieved. The resulting band-pattern does not interfere normally with the more or less non-polar phenolic compounds which are associated with natural soil humic substances. The extraction step has been extremely simplified with regard to the quantity of the soil sample and of the extractant. The accuracy of this procedure has been ascertained by means of recovery experiments with an artificial soil enriched with PAH. A single spot application mode and an evaluation scheme allow the estimation of EPA-PAH16 contents of soil samples in relation to threshold values ¶(1 or 5 or 10 mg/kg). This HPTLC screening method has been compared against standard HPLC methods. The simplified extraction step and the separation by HPTLC minimizes the actual costs and the time spent per sample.
Determination of Cu, Pb, Cd, and Zn in river sediment extracts by sequential injection anodic stripping voltammetry with thin mercury film electrode by C. L. da Silva; J. C. Masini (pp. 284-290).
Determination of Cu, Pb, Cd and Zn was performed in sediment extracts obtained according to the three steps sequential extraction procedure proposed by the European Community Standards, Measurements and Testing Program. The metal content was determined by anodic stripping voltammetry with a thin mercury film electrode controlled by a sequential injection (SIA) system. The proposed method improved the reproducibility of conventional anodic stripping voltammetry, as well as the sample throughput, allowing analysis of 30 to 45 samples per hour. The influence of flow rate and sample volume was studied to achieve an adequate sensitivity for the leachate studied. No interferences due to adsorption of organic matter, colloids, or complexes with slow rate of dissociation were observed. The intermetallic formation of Cu-Zn was avoided by forming the mercury film in presence of Ga(III) ions in the SIA system, resulting in low consumption of reagent in comparison to flow injection or continuous flow systems. Results were in good agreement with those obtained by Induced Coupled Plasma – Atomic Emission Spectroscopy (ICP- AES).
Microwave-assisted extraction method for the determination of atrazine and four organophosphorus pesticides in oranges by gas chromatography (GC) by A. Bouaid; A. Martín-Esteban; P. Fernández; C. Cámara (pp. 291-294).
A simple and rapid microwave assisted extraction (MAE) method is presented for the determination of atrazine and four organophosphorus pesticides (parathion-methyl, chlorpyriphos, fenamiphos and methidathion) in orange peel. The experimental variables that affect the MAE method, such as temperature, sample quantity, extraction time, nature and volume of organic solvents, were optimized. The MAE method was optimized using an experimental design. The results suggest that temperature and sample quantity are statistically significant factors. It was concluded that the five pesticides could be efficiently extracted from 1.5–2.5 g of orange peel with 10 mL of hexane/acetone (1 : 1) mixture at 90 °C in 9 min with microwave power set at 50% (475 W). After optimization these factors, recoveries ranged from 93 to 101% with a relative standard deviation ranging from 1 to 3%. The extracts were analyzed by gas chromatography with a nitrogen-phosphorus detector (GC-NPD).
Electrothermal vaporization system using furnace-fusion technique for the determination of lead in botanical samples by inductively coupled plasma atomic emission spectrometry by Y. Okamoto (pp. 295-299).
A new approach to sample digestion, subsequent vaporization and introduction into an inductively coupled plasma atomic emission spectrometer was developed for the direct determination of lead. To each small sample cuvette made of tungsten, a mixture of a ground solid sample and powdered diammonium hydrogenphosphate was precisely weighed. The cuvette was positioned onto the tungsten boat furnace (TBF) incorporating a vaporizer. Tetramethylammonium hydroxide solution was added. Then the cuvette was heated and maintained at a wet-digestion temperature to decompose the solid sample. After digestion, the temperature was elevated to generate the analyte vapor for introduction into a plasma. Since the solid samples were wet-digested in the sample cuvettes before vaporization, they could be analyzed by using a calibration curve prepared from aqueous standard solutions. This method was applied to the determination of lead in several biological materials with satisfactory results.
Direct determination of lead in biological samples by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) after furnace-fusion in the sample cuvette-tungsten boat furnace by Y. Okamoto (pp. 300-305).
The newly conceived electrothermal vaporization (ETV) system using a tungsten boat furnace (TBF) sample cuvette was designed for the direct analysis of solid samples with detection by inductively coupled plasma mass spectrometry (ICP-MS). Into this small sample cuvette, a solid mixture of the biological samples and diammonium hydrogenphosphate powder as a fusion flux was placed and situated on a TBF. Tetramethylammonium hydroxide solution was added to the mixture. After the on-furnace digestion had been completed, the analyte in the cuvette was vaporized and introduced into the ICP mass spectrometer. The solid samples were analyzed by using a calibration curve prepared from the aqueous standard solutions. The detection limit was estimated to be 5.1 pg of lead, which corresponds to 10.2 ng g–1 of lead in solid samples when a prepared sample amount of 1.0 mg was applied. The relative standard deviation for 8 replicate measurements obtained with 100 pg of lead was calculated to be 6.5%. The analytical results for various biological samples are described.