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Analytical and Bioanalytical Chemistry (v.365, #4)
Fundamental and practical aspects in the design of nanoscaled SnO2 gas sensors: a status report by N. Barsan; Markus Schweizer-Berberich; Wolfgang Göpel† (pp. 287-304).
Gas sensors based on semiconducting materials have become of great interest to both sensor users and researchers. In this context, a huge number of publications have appeared in the literature which deal with metal oxide gas sensors, in general, and with the prototype material SnO2, in particular. The amount of data published grows continuously and has led to a situation in which even experts in this field tend to lose an overview. The present review describes the reasons for this complexity and outlines unifying concepts to understand the huge amount of published, mostly empirical data. This leads to a comprehension of gas-sensing phenomena in both the application and research domains.
New applications of the retention index concept in gas and high performance liquid chromatography by I. G. Zenkevich (pp. 305-309).
New methods for the precalculation of GC retention indices (RIs) are discussed. The first is based on a new modification of the correlation equation log RI = a logTb + bA + c and is recommended for low boiling compounds of the general type R-X with known boiling points (Tb) analyzed on polymer sorbent Porapack Q. The second method permits one to predict RIs of products of organic reactions A + B → C +… with the correlation ΔRI = a ΔE + b (a < 0,|ρ| > 0.9), where ΔRI = RIC– RIA– RIB and ΔE = EC– EA– EB– are the differences in the internal molecular energies of reagents and products of organic reactions which are estimated by molecular dynamics methods. In the final section new possibilities of the use of RIs in reversed phase HPLC, namely for the determination of the number of hydroxyl groups in phenols, are illustrated.
A sensor for the in situ determination of acidity levels in concentrated sulfuric acid by B. Hammouti; H. Oudda; A. El Maslout; A. Benayada (pp. 310-313).
A potentiometric method at imposed weak current between two paste electrodes, ferrocene and chloranil, permits the in situ determination of sulfuric acid concentrations (0.5–11.0 M). The different factors affecting the potential at imposed current as current intensity, temperature and H+ ion concentration are studied. The potentials measured between ferrocene and chloranil electrodes are directly linked to the acid concentration. The acidity Ri(H) function, which represents the determination of the H+ activity has been determined and compared to Strehlow Ro(H), Janata HGF and Hammet Ho functions. Ri(H) is numerically equal to the thermodynamic Ro(H).
Preparation of an ion-selective electrode by chemical treatment of copper wire for the measurement of copper(II) and iodide by batch and flow-injection potentiometry by D. Dobčnik; M. Kolar; J. Komljenović; Nj. Radić (pp. 314-319).
The preparation of an ion-selective electrode by chemical treatment of copper wire and its application for the measurements of copper (II) and iodide ions is described. The proposed reaction mechanism at the sensing surface, which explains the response of the electrode to Cu2+ and iodide ions, is discussed. The prepared electrode was suitable for direct potentiometric measurements of iodide and copper (II) in batch experiments down to concentrations of 1 × 10–5 mol L–1. A tubular electrode, prepared in the same way, may be used as a potentiometric sensor in a flow-injection analysis for Cu (II) and/or iodide determinations.
Laser ablation-atomic fluorescence approach for the determination of mercury by C. M. Rico; J. M. Fernández-Romero; M. D. Luque de Castro (pp. 320-324).
A method for the determination of mercury in solid samples using laser ablation coupled with atomic fluorescence spectroscopy has been developed. An Nd-YAG laser was used for ablation and the vaporised and atomised material was rapidly led to an atomic fluorescence detector, where excitation and emission took place. The experimental approach was applied to the assessment of different procedures as sensitive as possible for implementing standard addition methods. Calibration curves were recorded using the prepared standards, which exhibited linear ranges between 0.5–100 μg/g, with excellent regression coefficients in all instances (0.9907). The precision, expressed as RSD %, was 3 and 4% for contents of 1 and 30 μg/g, respectively, in the same pellet; and 7 and 12% for the same contents and different type of pellets. The method has been applied to the determination of mercury in CRM of sewage sediment and a sludge sample with a known amount of mercury determined by an interlaboratory study. The results obtained show good agreement with those expected.
Optimization of the gravimetric determination method of nickel as dimethylglyoximate for nickel raw materials by P. Junnila; M. Latvala; R. Matilainen; J. Tummavuori (pp. 325-331).
The method parameters of an almost one century old method for analyzing nickel as dimethylglyoximate were critically examined for the analysis of nickel raw materials and many of the method parameters were observed to have a significant effect on the Ni recovery. Thus, because the Ni precipitation method parameters vary a lot in analytical literature and also in practice, the obtained Ni results by different methods are not comparable. During this study it was found that the double precipitation worked out perfectly in eliminating the effects of impurity elements. The residual Ni content in the filtrates should also be measured to obtain accurate and precise Ni results. In complexing the impurity elements, tartaric acid, stabilized by acetic acid, turned out to be effective, and when added to the sample solution before ammonium addition, the best pH conditions for homogenous Ni precipitation with dimethylglyoxime were obtained. The optimized Ni determination method described was found to be accurate and highly reproducible when tested with Ni concentrates and standard reference materials containing high Ni concentrations.
Elemental analysis of airborne dust samples with TXRF: Comparison of oxygen-plasma ashing on sapphire carriers and acid digestion for sample preparation by M. Theisen; R. Niessner (pp. 332-337).
The concentrations of 13 elements (As, Ca, Co, Cd, Cr, Fe, Ga, Ni, Pb, Pt, Ti, V and Zn) were determined in air particulate matter using total reflection X-ray fluorescence spectrometry (TXRF). For silicon analysis synthetic sapphire was chosen as a new sample carrier material – it is silicon-free, resistant to oxygen-plasma, microwaves and concentrated acids. The dust samples were collected on cellulose acetate filters. The decomposition of the filters was carried out by oxidation in a microwave-generated low-pressure oxygen-plasma directly on the TXRF sample carriers. The recovery of the investigated elements was verified with the standard reference material SRM 1648 (urban particulate matter) and ranged from 90 to 97%. The oxygen-plasma method was compared with conventional sample preparation by acid digestion.
A multiresidue method with mobile on-site sampling based on SPE for ultratrace analysis of plant protectants in environmental waters by K. Pittertschatscher; Norbert Inreiter; Andrea Schatzl; Hans Malissa (pp. 338-350).
A new multiclass/multiresidue method for monitoring plant protectant residues in raw- and drinking waters with on-site sampling using a mobile, self-contained sampling unit based on SPE was developed and validated. 38 active compounds with widely varying chemical and physicochemical properties (acid-base properties, polarities, vapor pressures, solubilities) are measured from just one sample and work-up. 100 mL water, acidified with acetic acid, are drawn through a cartridge filled with Amberchrom resins by means of a calibrated 100 mL syringe driven by servo motors, control circuit and rechargeable battery. Volumetric flow is high, quantitative extraction of acidic, neutral and weak basic substances is accomplished in a few minutes and loaded cartridges are transported into the laboratory. Further work-up, i.e. elution, drying, concentration and solvent change, is designed strictly non-selectively and produces 250 μL of an “extract”, which is the starting point of two GC measurement lines, GC-NPD and GC-ECD. Chlorinated herbicide acids are derivatised into perfluorinated benzyl esters employing reaction conditions so smooth that the organochlorine hydrocarbons are not destroyed at all and both substance classes can be chromatographed in one GC run. ECD-chromatograms from derivatised solutions are rather complex, therefore the flow is split after injection onto two columns with different polarities and two EC-detectors in order to resolve all analytes and matrix interferents. Short-chain carbonic acids added to the water prior to preconcentration are adsorbed on the hydrophobic surface in a reversible process and impart the Amberchrom resins with a partially hydrophilic character. Method performance was ascertained using tap water fortified at the 0.2 μg L–1 level: Mean recoveries were between 70 and 115% and method detection limits (MDLs) below 0.08 μg L–1. Waters from different sources did not affect the recoveries, loaded cartridges are stable for two weeks’ storage when cooled.
Direct solventless supercritical fluid extraction of chlorbiphenyls from aqueous solutions at 0.1 × 10–12 g/g level and whole extract analysis by GC/ECD by I. N. Glazkov; I. A. Revelsky; I. P. Efimov; Yu. A. Zolotov (pp. 351-354).
A method of PCB determination in water based on direct supercritical fluid extraction (SFE) and off-line solventless SFE/GC coupling has been developed. High SFE recovery of the targeted compounds from water and high efficiency of their solventless transfer into GC were achieved. The method can be used for fast screening of water samples for PCBs at ultratrace levels.
Investigation of SFE/SFC grade carbon dioxide by Dirk C. Hinz; B. W. Wenclawiak (pp. 355-360).
Carbon dioxide, the most used substance for supercritical fluid extraction, was investigated for its purity. The carbon dioxide containing impurities were concentrated in a cold trapping system and analyzed by GC-FID, -ECD and -MS. It was possible to identify several of these impurities. For some SFE pumps a helium headpressure is required. The influence of different headpressures and different types of gases on impurity level was also investigated.
Collaborative study to improve the quality control of trace element determinations in polymers. Part 1. Interlaboratory study by W. Van Borm; A. Lamberty; Ph. Quevauviller (pp. 361-363).
In order to control the quality of trace element determinations in polymer, the Standards, Measurements and Testing Programme (formerly BCR) of the European Commission has started a project of which the final aim is to certify polymer reference materials for their contents of a range of trace elements. The first part of this project consisted in an interlaboratory study which aimed at testing the feasibility of preparation of candidate polymer reference materials and to detect and remove most of the pitfalls observed in trace element determinations. This paper presents the results of this interlaboratory study carried out prior to the certification campaign.
Novel photolytic decomposition method of organic compounds with a high output low-pressure mercury lamp for voltammetric trace metal analysis by K. Yokoi; Maki Yakushiji; Mayumi Hatanaka; Koji Kubono; Tsutomu Koide (pp. 364-367).
A high output low-pressure mercury lamp, 400 W L-Hg, was successfully used for the photolytic decomposition of dissolved oganic compounds as the pretreatment for the determination of trace metal ion in aqueous solution by stripping voltammetry. Various amino acids, showing interferences on voltammetric determination of metal ions, can be removed quite easily by intensive UV irradiation at room temperature. Effect of pH, concentration of electrolyte and dissolved oxygen on the efficiency of photolysis are also described. This method uses no additional chemicals such as acids or oxidants and can be carried out in closed clean conditions.
Determination of metal traces in wine by argon stabilized d.c. arc by S. Ražić; Marija Todorović; Ivanka Holclajtner-Antunović; Milovan Stoiljković (pp. 367-370).
A spetroscopic method for the determination of metal traces (Mn, Cu, Fe) in wine has been developed based on argon stabilized d.c. arc plasma at atmospheric pressure. The experimental conditions were optimized using lateral distributions of spectral line intensities of the trace elements in aqueous and ethanol-aqueous solutions. The method was applied to the analysis of 6 wines from 3 Serbian wine-growing regions. Direct and standard addition methods were tested. The precision of the method is characterized by a relative standard deviation of 0.50– 3.00%. The accuracy of the method was assessed by flame AAS.
Indirect atomic absorption spectrometric determination of citric acid by continuous precipitation by M. C. Yebra; R. M. Cespón (pp. 370-373).
A continuous precipitation and filtration flow system for the separation of citric acid by precipitation with lead and indirect flame atomic absorption spectrometry is proposed. The precipitate is formed by injecting the lead solution into a carrier containing the sample and is subsequently retained on a filter. By using this reversed precipitation flow-injection configuration, citric acid was determined in the range 2–40 μg mL–1, with a relative standard deviation of 2.9% at a sampling frequency of 60 samples h–1. This method has been applied to the determination of citric acid in fruit juices, carbonated soft drinks and sweets.
Application of fluoroxidants for the decomposition and analysis of platinum metals and gold in black shale ores by V. N. Mitkin; A. A. Galitsky; T. M. Korda (pp. 374-376).
In order to develop a reliable method for the platinum group metals (PGMs) determination in ores of organic origin like carbonaceous black shale a decomposition method with fluoroxidants like BrF3 and KBrF4 was established which avoids the commom losses of PGM organometallic compounds by volatilazation or chemisorption. The recovery from different trapping solutions is discussed. Platinum metals are evidently found in the carbonaceous black shale ores from the “Natalka” deposit situated in the Magadan area. PGMs are very inhomogenously distributed in the ores and ore concentrates and their total contents in ore are 5–18 g/t. The carbonaceous concentrate of black shale ore contains up to 23 g/t of the sum of platinum metals. ≥ 8% of the sum of platinum and palladium contained in this carbonaceous concentrate are soluble in organic solvents.
Sequential determination of carbon dioxide and free sulfur dioxide in wine by flow-injection pervaporation with in series potentiometric-photometric detection by E. Mataix; M. D. Luque de Castro (pp. 377-380).
A method for the simultaneous determination of CO2 and free SO2 in wines based on the use of a continuous arrangement coupled to both a pervaporator and in series arranged potentiometric and photometric detectors is proposed. After pervaporation, both analytes give one common potentiometric signal and then the free SO2 is photometrically determined via the colored compound formed with p-rosaniline and formaldehyde. The CO2 content is determined by difference. The range of the method is linear between 2.0 and 20.0 mg/L for free SO2 and 50.0 and 600.0 mg/L for CO2, with a precision, expressed as relative standard deviation, of 7% in both cases. The method was applied to different Spanish wines and the results compare well with those obtained by the corresponding official methods.
A novel chemiluminescence flow-through sensor for the determination of analgin by Yu-Ming Huang; Chao Zhang; Xin-Rong Zhang; Zhu-Jun Zhang (pp. 381-383).
A novel chemiluminescence (CL) flow-through sensor for the determination of analgin with flow-injection analysis (FIA) based on the auto-oxidation of analgin in the presence of Tween 80 sensitized by Rhodamine 6G immobilized on a cation-exchange column is described. This sensor responds linearly to the analgin concentration in the range of 0.4 ∼ 10 mg/L, with a detection limit (3σ) of 0.15 mg/L. A complete analysis, including sampling and washing, takes 1 min with a relative standard deviation of < 5%. The sensor is stable for over 200 determinations and has successfully been applied to the determination of analgin in pharmaceutical preparations.
Rapid spectrophotometric method to resolve ternary mixtures of Tartrazine, Quinoline Yellow and Patent Blue V in commercial products by J. J. Berzas Nevado; J. Rodríguez Flores; M. J. Villaseñor Llerena; N. Rodríguez Fariñas (pp. 383-388).
A very simple spectrophotometric method is described for resolving ternary mixtures of the food dyes Tartrazine (E-102), Quinoline Yellow (E-104) and Patent Blue V (E-131) by using the second derivative of the spectra with measurements at zero-crossing wavelengths. Calibration graphs are linear up to 20.0 mg/L of Tartrazine, up to 20.0 mg/L of Quinoline Yellow and up to 6.4 mg/L of Patent Blue V. Repeatability and reproducibility studies (with the Students’s and F tests) were achieved for two series of nine standards for each dye showing no significant differences at the 95% confidence level. Detection limits of 0.0526, 0.0164 and 0.0034 mg/L were obtained for Tartrazine, Quinoline Yellow and Patent Blue V, respectively. This method was used for determining synthetic mixtures of these colorants in different ratios and it was successfully applied to four commercial products without previous separation step. The results found in commercial products were compared with those obtained by an HPLC method and very similar values were found for both methods.