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Analytical and Bioanalytical Chemistry (v.363, #3)
On-line analysis of the photoacoustic spectral signal using wavelet transform by Xueguang Shao; Wan Li; Gang Chen; Qingde Su (pp. 215-218).
An on-line wavelet transform (WT) algorithm was proposed and successfully used in processing the photoacoustic (PA) signal. By investigating the spectra of three rare earth compounds, it was indicated that after on-line decomposition by WT, the noise in the PA spectra was cleanly removed, and the resolved information in the overlapping peaks was easily retrieved. The effect of different sampling rate on resolved results was also investigated. The experimental results showed that the position of peaks after decomposition agreed with the corresponding intramolecular energy transition bands, which demonstrated that WT is a useful and efficient tool for the study of energy bands of rare earth compounds using PA spectroscopy.
Multicomponent determination of cobalt, copper, and iron with 1,10-phenanthroline by principal component regression modelling of spectrophotometric data by M. Kompany-Zareh; A. Massoumi (pp. 219-223).
A spectrophotometric method for the simultaneous determination of Co, Cu, and Fe in ternary mixtures by means of 1,10-phenanthroline as a complexing agent was developed. The influence of chemical variables affecting the analytical reaction was evaluated. A principal component regression procedure was used to assess spectrophotometric data obtained from nineteen calibration solutions. The method was validated by applying it to the analysis of synthetic mixtures over the concentration ranges 0–407 μmol Co/L, 0–189 μmol Cu/L, and 0–143 μmol Fe/L. It was also successfully employed for the analysis of two cobalt magnetic alloys. The relative errors in the determinations were less than 7% in most cases.
Determination of Cu, Zn and Cd in water by FAAS after preconcentration by baker’s yeast (Saccharomyces cerevisiae) immobilized on sepiolite by Hüseyin Bağ; Mustafa Lale; A. Rehber Türker (pp. 224-230).
By using the adsorbent Saccharomyces cerevisiae immobilized on sepiolite an adsorption-elution method was developed for the preconcentration of Cu, Zn, and Cd followed by flame atomic absorption spectrometry (FAAS). Recoveries were 98.3 ± 0.4% for Cu, 94.2 ± 0.3% for Zn, and 99.04 ± 0.04% for Cd at 95% confidence level obtained by the column method. The influence of sea water matrix elements on the separation of the trace elements was also assessed by using the column procedure. The breakthrough capacities were found to be 74 μmol/g for copper, 128 μmol/g for zinc and 97 μmol/g for cadmium. After optimization the proposed method was applied to the trace metal determination in sea and river water.
Comparison of μm and mm sized disk electrodes for end-column electrochemical detection in capillary electrophoresis by Frank-Michael Matysik; L. Nyholm; Karin E. Markides (pp. 231-235).
End-column electrochemical detection based on either the use of a 25 μm microdisk electrode or a 0.5 mm macrodisk electrode has been compared with respect to performance and influence on non-aqueous capillary electrophoretic separations. Despite the much higher coulometric efficiency obtained with the larger disk electrode, the microdisk electrode configuration offers comparable limits of detection (LOD) for the neutral and positively charged ferrocene compounds employed in conjunction with a non-aqueous acetonitrile-based buffer. The LODs for ferrocene were found to be 4.0 × 10–8 M and 6.7 × 10–8 M for the microdisk and macrodisk detector, respectively. In addition, both detector arrangements showed different relative responses for neutral and positively charged analytes. The macroelectrode-based detector introduced additional zone broadening while this was not found to be the case with the microelectrode arrangement. Using the microelectrode detector, the band broadening in an electro-osmotically driven flow system was compared to that in a gravity flow-based system. It was demonstrated that the zone broadening under gravity flow conditions was approximately twice as large as under electro-osmotic flow conditions for a typical set of experimental parameters.
Electrocatalytic reduction of nitrite on the surface of a glassy carbon electrode modified by palladium(II)-substituted Dawson type heptadecatungstodiphosphate by Wenliang Sun; Yuezhong Xian; Huizhang Liu; Wen Zhang; Litong Jin (pp. 236-240).
A palladium(II)-substituted Dawson type heptadecatungstodiphosphate, K8[P2W17O61Pd(H2O)](abbreviated as P2W17Pd in the following), was used to construct a new kind of chemically modified electrode (CME) by electrodeposition on the surface of a glassy carbon electrode for the first time. This modified electrode was characterized by Fourier transform infrared reflection absorption spectroscopy (FTIRRAS), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). FTIRRAS and XPS suggested that the adsorbed species on the electrode surface has the same Dawson type structure as the heteropolyanion in buffer solution. A couple of waves was observed on the P2W17Pd CME, which was ascribed to the redox process of the palladium center in the heteropolytungstate. After continuous potential scanning for 30 min in a pH 4.0 buffer, 94% of the original coverage remains for the CME. The P2W17Pd CME had high electrocatalytic activity for nitrite reduction and exhibited good reproducibility and stability. The catalytic peak current was found to be linear with the nitrite concentration in the range of 1 ∼ 50 mmol/L, with a correlation coefficient of 0.994. The effect of solution pH on the catalytic activity of the CME for nitrite reduction was also investigated.
End-point detection of the potentiometric titration of anionic polyelectrolytes using an anionic surfactant-selective plasticized poly (vinyl chloride) membrane electrode and an anionic surfactant as a marker ion by T. Masadome; Toshihiko Imato; Yasukazu Asano (pp. 241-245).
A plasticized poly (vinyl chloride) (PVC) membrane electrode sensitive to dodecylbenzenesulfonate (DBS) ion is applied to the determination of anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) by potentiometric titration, using a poly (diallyldimethylammonium chloride) (Cat-floc) solution as a titrant. The end-point of the titration is detected as the potential jump of the plasticized PVC membrane electrode caused by decrease in the concentration of DBS ion added to the sample solution as a marker ion, due to the ion association reaction between the DBS ion and Cat-floc. The effects of the concentration of DBS ion, coexisting surfactants and electrolytes in the sample solution and pH of the sample on the degree of the potential jump at the end-point were examined. A linear relationship between the concentration of anionic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 2 × 10–5 to 4 × 10–4 N for PVSK, alginate, and carrageenan.
Enhancement of the sensitivity and selectivity of oxidation of H2O2 on platinum wire at low working potential by platinization and covering of heteropolypyrrole film for amperometric micro-biosensor construction by Qing-Shan Li; Bang-Ce Ye; Bai-Xiang Liu; Jian-Jiang Zhong (pp. 246-250).
A microelectrode for glucose determination was constructed by immobilization of glucose oxidase (GOx) on a platinized platinum (Pt) by electrochemical polymerization of a solution containing GOx, pyrrole, and a substituted pyrrole, 4-(3-pyrrolyl)-4-oxobutyric acid. Due to platinization and covering with the polymerized heteropolypyrrole (hPPy) film, the electrode prepared showed high sensitivity to H2O2 at a low potential and significantly reduced the response to electroactive compounds, such as ascorbate, urate and 4-acetamidophenol. Working at 200 mV (vs. SCE) the electrode showed a linear response to glucose from 1.6 to 10 mM with a high sensitivity of 1 μA/mM, whereas the response to 1 mM ascorbate, urate, and 4-acetamidophenol was 0.53 μA, 18 nA and 4 nA, respectively, which was about 2.5%, 1.0% and 1.0% of that at a bare electrode. The stability of the electrode was tested at intervals of three or five days, and each test lasted about two hours. After 6 months examination, only 30% of its activity was lost.
Preconcentration of trace elements in sea water with poly (acrylaminophosphonic – dithiocarbamate) chelating fiber for their determination by inductively coupled plasma mass spectrometry by B. Wen; X.-Q. Shan; Rui-Xia Liu; Hong-Xiao Tang (pp. 251-255).
A new ion exchange chelating fiber with aminophosphonic and dithiocarbamate groups based on polyacrylonitrile was used for the simultaneous preconcentration of beryllium, bismuth, cobalt, gallium, silver, lead, cadium, copper, manganese and indium in sea water. The optimum experimental parameters, such as fiber capacity, pH, sample flow rate and volume, eluant and effect of matrix ions on the preconcentration were investigated. The separation of analytes can be achieved from sea water with a concentration factor of at least 200 times. The method has been applied for the determination of trace elements in coastal sea water. The data obtained by this method agreed well with certified values.
Dioctyltin and tributyltin detection at trace levels in water and beverages by capillary gas chromatography with flame photometric detection by G. B. Jiang; F. Z. Xu; F. J. Zhang (pp. 256-260).
A simple chromatographic procedure has been developed for the sensitive determination of dioctyltin and tributyltin compounds in water and beverages. Dioctyltin and tributyltin react with NaBH4 at pH 5 to produce volatile hydrides which can be quantitatively extracted into CH2Cl2. The corresponding dioctyltin hydride derivative is identified by HPLC-ES-MS and measured by flame photometric detection using the quartz surface-induced tin emission. Detection limits of less than 0.7 pg of tributyltin and 10 pg of dioctyltin were achieved. Results showed that up to 9.5 ng/mL levels of dioctyltin were present in beverages.
Separation of copper (II) ions from humic complexes with oxine-impregnated emulsion globules by Masataka Hiraide; Koh Hasegawa (pp. 261-264).
A water-in-oil type emulsion containing oxine has been used for the discrimination of copper(II) ions and copper-humic complexes in aqueous solutions. A toluene solution containing oxine and nonionic surfactant (Span-80) was vigorously mixed with 1 mol/L HCl by ultrasonic irradiation. The resulting emulsion was added to water and dispersed by stirring as numerous small globules. Copper(II) ions were quantitatively permeated across the oil layer and incorporated in the tiny droplets of HCl, whereas copper-humic complexes remained in the sample solution. After collecting the dispersed emulsion globules, they were destroyed by heating to segregate the aqueous (HCl) and organic (toluene) phases. The copper in the aqueous phase was determined by graphite-furnace atomic absorption spectrometry (GFAAS). The analytical results agreed with those obtained by the adsorption method, where negatively charged humic complexes were selectively collected on a macroreticular anion exchanger Sephadex A-25 column. The conventional liquid-liquid extraction did not offer a chemical speciation because copper(II) ions and humic complexes were simultaneously extracted into the organic phase. The proposed emulsion method was successfully applied to the analysis of river water samples.
Flow injection-solid phase spectrofluorimetric determination of pyridoxine in presence of group B-vitamins by A. Ruiz-Medina; M. L. Fernández-de Córdova; A. Molina-Díaz (pp. 265-269).
A flow-through optosensor has been prepared for the sensitive and selective determination of pyridoxine (vitamin B6) in aqueous solutions. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric detection using Sephadex SP-C25 resin as an active sorbent substrate. This method of determination is carried out without any derivatization. The wavelengths of excitation and emission were 295 and 385 nm, respectively. When a HCl (10–3 mol L–1) / NaCl (3 × 10–2 mol L–1) solution is used as carrier solution, the sensor responds linearly in the measuring range of 5–200, 10–400 and 50–1800 ng mL–1 with detection limits of 0.33, 0.67, and 5.70 ng mL–1 for 2000, 1000 and 200 μL of sample volume, respectively. The relative standard deviation for ten independent determinations is less than 0.75% for 0.2 and 1.0 mL of sample volumes used, and 1.31% for 2.0 mL of sample volume used. The method was satisfactorily applied to the determination of vitamin B6 in pharmaceutical preparations.
Study of the electrochemical behaviour of amphetamine and its derivatives in aqueous solution by T. Keller; Martin Mutz; Rolf Aderjan; Hans Peter Latscha (pp. 270-276).
The polarographic behaviour of amphetamine-type drugs in acid and alkaline solutions was investigated. Differential pulse polarography (DPP) with a dropping mercury electrode (DME) was used to monitor these drugs in aqueous solution. DPP and cyclic voltammetry (CV) were also utilised to study the electrode process of some 2-phenylethylamines derivatised with 4-N,N-dimethylaminobenzaldehyde (Ehrlich’s reagent) and 2,4-dinitrofluorobenzene, known as Sanger’s reagent, respectively.
Determination of lanthanum and rare earth elements in bovine whole blood reference material by ICP-MS after coprecipitation preconcentration with heme-iron as coprecipitant by Eiji Fujimori; Tatsuya Hayashi; Kazumi Inagaki; H. Haraguchi (pp. 277-282).
An analytical method for the determination of lanthanide elements in the bovine whole blood reference material (IAEA A-13) has been investigated by inductively coupled plasma mass spectrometry (ICP-MS). The bovine whole blood reference material was digested with HNO3 and HClO4, and then the pH of the digested solution was adjusted to 12 with 3 M sodium hydroxide aqueous solution. In this experimental procedure, lanthanide elements in the blood sample were coprecipitated with iron mainly derived from heme-iron in blood itself. In order to minimize matrix effects due to iron, excess iron in the analysis solution was removed by solvent extraction using methyl isobutyl ketone (MIBK) prior to the determination of lanthanide elements by ICP-MS. The recoveries of all lanthanide elements were almost quantitative in the recovery test. In consequence, it has been found that all lanthanide elements in bovine whole blood reference material are at the wide concentration range of 0.90 pg/g for Tm ∼1880 pg/g for Ce.
Determination of cadmium and lead in mussels by electrothermal atomic absorption spectrometry using an ultrasound-assisted extraction method optimized by factorial design by I. Lavilla; J. L. Capelo; C. Bendicho (pp. 283-288).
A simple and rapid method is described for the quantitative extraction and determination of Cd and Pb in mussel tissue (Mytilus edulis). The method is based on the quantitative ultrasound-assisted extraction (i.e. sample mass at mg level) of the two metals using diluted nitric acid as extractant. The extraction procedure is carried out in autosampler cups of the graphite furnace (typically, less than 20 mg). A two-level full factorial design (24) was applied to optimize the variables influencing the ultrasound extraction process. These variables were: extraction time, ultrasound amplitude, nitric acid concentration and particle size. Optimization results showed that acid concentration and particle size were the more significant variables. Determination of Cd and Pb in extracts obtained after ultrasound treatment was carried out by Electrothermal Atomic Absorption Spectrometry. The method was validated by statistically comparing the metal contents found with the certified ones corresponding to the BCR 278 mussel tissue. No significant differences were observed for P = 0.05. LODs for Cd and Pb in mussel tissue were 0.019 and 0.37 μg g–1. RSDs values (corresponding to between-batch precision for n = 5) were 2.2 and 6.7% for Cd and Pb, respectively. The method was applied to measure the contents of Cd and Pb in mussels used as pollution bioindicators from the Galician coast (Ria de Vigo, Spain).
Validation of a high-performance chromatographic method for determination of cefotaxime in biological samples by Juan Agüero; José-Esteban Peris; Eduardo San-Martín (pp. 289-293).
An analytical method for detecting and quantifying cefotaxime in plasma and several tissues is described. The method was developed and validated using plasma and tissues of rats. The samples were analyzed by reversed phase liquid chromatography (HPLC) with UV detection (254 nm). Calibration graphs showed a linear correlation (r > 0.999) over the concentration ranges of 0.5–200 μg/mL and 1.25–25 μg/g for plasma and tissues, respectively. The recovery of cefotaxime from plasma standards prepared at the concentrations of 25 μg/mL and 100 μg/mL was 98.5 ± 3.5% and 101.8 ± 2.2%, respectively. The recovery of cefotaxime from tissue standards of liver, fat and muscle, prepared at the concentration of 10 μg/g was: 89.8 ± 1.2% (liver), 103.9 ± 6.5% (fat) and 97.8 ± 2.1% (muscle). The detection (LOD) and quantitation (LOQ) limits for plasma samples were established at 0.11 μg/mL and 0.49 μg/mL, respectively. The values of these limits for tissues samples were approximately 2.5 times higher: 0.3 μg/g (LOD) and 1.25 μg/g (LOQ). For plasma samples, the deviation of the observed concentration from the nominal concentration was less than 5% and the coefficient of variation for within-day and between-day assays was less than 6% and 12%, respectively. The method was used in a pharmacokinetic study of cefotaxime in the rat and the mean values of the pharmacokinetic parameters are given.
Use of a single calibration graph for the determination of major elements in geological materials by laser ablation inductively coupled plasma atomic emission spectrometry with added internal standards by V. Kanicky; Jean-Michel Mermet (pp. 294-299).
The possibility of internal standardisation in laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES) of geological materials by added Sc2O3 and Y2O3 has been examined to cover the wide range of concentrations of major and minor constituents both in silicate rocks and limestones. A Nd : YAG laser (355 nm, 10 Hz, 10 mJ per shot) was used for the ablation of discs obtained by fusion of the mixture of samples and oxides of Sc and Y with lithium tetraborate. The flux/sample ratio was in the range from 6 to 10. The contents of analytes were within the concentration range from hundredths to tens of percentage. The trace elements copper and nickel were studied, too. An ICP emission spectrometer OPTIMA 3000 DV was used for the measurement of Si, Al, Ca, Mg, Sr, Ba, Fe, Ti, Mn, Ni, Cu, Na and K analyte lines and Y and Sc reference lines in the axial observation mode. The long-term and the short-term repeatability of measurement were improved by employing scandium or yttrium internal references lines for the above analytes from 6% to 1.5% of RSD and from 2.4% to 1.0% of RSD, respectively. The correlation of signals with concentrations was improved in terms of the correlation coefficient r from 0.90–0.97 to 0.98–0.998 and the relative uncertainity on the centroid of concentrations was improved 2–3 times. A single calibration graph covering the concentration range both in silicates and carbonates is possible for each of elements, as the matrix effects are compensated for by internal standards and the excess of Li2B4O7.
Microwave digestion of ancient peat and determination of Pb by voltammetry by D. Weiss; W. Shotyk; H. Schäfer; U. Loyall; E. Grollimund; M. Gloor (pp. 300-305).
Different acid compositions (HNO3, H2O2, HF and HClO4) and low pressure microwave digestion were applied to the microwave assisted dissolution of ancient peats. The digests were evaluated with respect to the decomposition of the inorganic and organic fraction of peats and to an optimised determination of Pb by differential pulse anodic stripping voltammetry (DPASV). Addition of hydrofluoric acid was necessary to achieve a complete dissolution of the resistant inorganic phase of the peat and to obtain the total Pb concentration. Addition of perchloric acid decreased the concentration of dissolved organic carbon significantly, enabling reliable voltammetric signals for Pb determinations with satisfying peak shape, baseline, sensitivity, and precision. The limit of detection for Pb in peats was 1 ng/mL in the acid digest, equivalent to 0.2 μg/g in solid peat. This allowed the determination of low, pre-industrial concentrations of Pb in peat bogs from various locations (Europe and SE Asia). A chelation column used to isolate the metals from the complex matrix to further improve the detection limits failed to provide good recoveries for the peats and plants.
An open microwave digestion of oxide materials continuously analyzed by ICP emission spectrometry by Jörg Flock; Frank Michael; K. D. Ohls (pp. 306-310).
A device for microwave digestion in an open system was designed, with which a slurry automatically produced from solid sample powders can be processed continuously and then be transported directly into the ICP spectrometer by an online method. The success of this procedure is dependent to a high degree on the behavior of the material to be analyzed and the instrumental device used. In principle, it can be easily installed in a laboratory by combining single units like a mill, a pump, a microwave oven, and an ultrasonic bath in front of an ICP spectrometer. As examples, converter sludge and sinter were processed. In contrast to the sludge, the sinter material was difficult to homogenize sufficiently well. This led to recovery problems, especially for oxides of Si, Al or Ti being separated from the matrix by long-time milling. To overcome the blocking of valves, an open microwave digestion system is applied here (as usual by acid attack). Furthermore, the ICP source is able to excite the particles of a slurry much more efficiently than any other flame. The sufficient results obtained for the online method described here showed it to be a fast method for routine analysis.
A robotics-potentiometric method for the determination of mercaptan sulfur in fuels by Alfredo Velasco-Arjona; María Dolores Luque de Castro (pp. 311-313).
A fully automated robotics method for the determination of mercaptan sulfur in several types of fuels is proposed. It is based on the standard method involving removal of sulfide with cadmium sulfate and subsequent determination. The robotics station develops both the preliminary operations and the determination. The method affords a precision, expressed as relative standard deviation, of 1.63%. The good agreement between the results obtained by the proposed and by conventional methods for the target analyte confirms its excellent performance and usefulness.
Optimised method of coal digestion for trace metal determination by atomic absorption spectroscopy by E. Ikävalko; T. Laitinen; H. Revitzer (pp. 314-316).
Understanding the transport of trace elements through a coal-fired power plant requires reliable analytical methods for these elements in all the ingoing and outgoing mass streams. Coal and different kinds of ashes comprise the most abundant mass streams in such a plant. As a continuation of our previous work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissolution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO3 (conc.) and HF (conc.) in the volume ratio of 50 : 1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO3 alone was used as the digestion acid.
Emulsion liquid membrane separation of As(III) and As(V) by Longquan Li; Ping Yan; Wenzhong Gao; Yadong Li (pp. 317-319).
Emulsion liquid membranes (ELM) consisting of L113A (surfactant), liquid paraffin (stabilizer) and kerosene (solvent), with HCl solution acting as the external phase and KOH solution acting as the internal phase, were applied to the prior separation of arsenic(III) and arsenic(V) with subsequent spectrophotometric determination by AgDDTC. The effect of various parameters on the recovery of arsenic(III) were investigated. 8 mol/L HCl was required for 95% As(III) recovery. After reduction of As(V) to As(III) with sufficient KI, total arsenic could be determined. The RSD of As(III) and As(total) were both less than 3%. The procedure was applied to aqueous samples with a recovery of 93.5%–101%.
FIA determination of pyruvate in serum based on direct chemiluminescence oxidation by Manliang Feng; Guofang Zhang; Zhujun Zhang (pp. 320-322).
Chemiluminescence was observed by mixing acidic potassium permanganate solution with pyruvate in the presence of quinine. A new simplified method for pyruvate determination based on this phenomenon was established. The chemiluminescence intensity is a linear function of the concentration of pyruvate in the range of 2 × 10–6 to 1 × 10–3 g/mL with a detection limit of 0.8 μg/mL and a relative standard deviation of less than 2.3%. The method has been successfully used to determine pyruvate in serum.