Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Analytical and Bioanalytical Chemistry (v.364, #4)
Thick-film graphite electrodes in stripping voltammetry by Kh. Brainina; G. Henze; N. Stojko; N. Malakhova; C. Faller (pp. 285-295).
Various types of modified thick-film graphite electrodes are reviewed. Two modification options are available: either in situ modified or beforehand. Electrodes modified in situ by various organic compounds were used for the determination of W, Mo, Cr, Ni and Mn by adsorptive stripping voltammetry. Insoluble inorganic salts, insoluble organic complexes or soluble compounds protected with Nafion were used for modification of the electrode surface beforehand. These pre-conditioned electrodes permit quantification of Pb, Cd, Cu, Zn, Sn, As and Hg ions. The detection limits of these elements were in the sub-μg/L range. The relative standard deviation did not exceed 10–15%. Measurements were made without deaeration of test solutions and normally without destroying small organic matter found in surface waters. A number of characteristics, such as the formation of well-shaped peaks and stable increments of peaks after standard additions, as well as elimination of the mechanical surface regeneration stage and metallic mercury or its soluble salts from the analytical procedure and a long shelf-life of the electrodes make them promising for electroanalysis and for application in portable field instruments.
In-situ atomic force microscopy investigation of aerosols exposed to different humidities by G. Köllensperger; G. Friedbacher; R. Kotzick; R. Niessner; M. Grasserbauer (pp. 296-304).
In-situ atomic force microscopy (AFM) studies were performed on aerosol samples showing the potential of a topochemical approach for gaining information on chemical and physical aerosol properties. The behavior of single sub-micron particles has been investigated with respect to changing humidity in the surrounding atmosphere. Volume calculations allowed monitoring of these changes on a quantitative basis. As expected these in-situ experiments showed the restructuring of particles with highly agglomerated chain-like structures induced by condensation and evaporation on a nanometer scale. The particle volumes decreased as the branched chain-like structure changed into a more regular clump-like structure. The degree of restructuring was clearly depending on the chemical surface properties as could be proven for soot-like test aerosol particles. The collapse of the chain-like structure on a nanometer scale was found to be significantly more pronounced for soot particles previously exposed to ozone. Furthermore, in-situ studies were performed on ammonium sulfate test aerosol. Though a distinct deliquescence point typical for salts could not be detected, neither in the topography nor in the phase image, ammonium sulfate test aerosol particles seemed to partially dissolve in humid atmosphere and hence to decrease in volume. Thus, the volume decrease induced by purging with humid nitrogen and subsequent drying which was also observed for a considerable fraction of urban aerosol, could be interpreted in terms of composition and surface properties considering the geometrical structure (i.e. state of agglomeration) of the particles.
Method performance of the closed vessel microwave-assisted acid extraction using 50% HNO3 : HCl (3 : 2) with positive pressure Teflon membrane filtration by A. Robbat jr.; Robert L. Simpson III (pp. 305-312).
The recovery from soil of 22 metals on the U.S. Environmental Protection Agency’s (EPA) Target inorganic analyte list is described. The extraction method was developed to provide a safe, rapid, and analytically reliable means of leaching metals from soils and sediments in one procedure. The influence of digestion matrices, filtration media, reference standard types and instrument performance of inductively coupled plasma/optical emission spectroscopy is presented. The method employs a closed vessel, temperature and pressure controlled, microwave acid digestion using 20 mL of 50% HNO3 : HCl in a ratio of (3 : 2). The digestate was filtered through a positive pressure Teflon membrane cartridge. This procedure recovered all metals at concentrations equal to or greater than what is possible by EPA standardized methods or other methods published in the literature. Excellent method precision and accuracy was obtained for all metals, especially Ag and Sb. Results show that the positive Teflon membrane filtration system yielded higher and statistically different concentrations of Mn, Zn, Cu, Fe, As, Cd, Pb, Ag, and Sb than paper filtration in half the time. These findings were produced from standard reference soils and soil collected from a hazardous waste site landfill.
Interaction between natural organic matter (NOM) and polycyclic aromatic compounds (PAC) – comparison of fluorescence quenching and solid phase micro extraction (SPME) by T. E. Doll; F. H. Frimmel; M. U. Kumke; G. Ohlenbusch (pp. 313-319).
The interaction of phenanthrene and 9-aminophenanthrene with natural organic matter (NOM) of different origin was investigated using the fluorescence quenching approach and the solid phase micro extraction method. The results of both methods are compared in terms of the influence of the concentration of the polycyclic aromatic compounds (PAC) as well as the concentration of the NOM on the observed binding constant. Due to the combination of steady-state and time-resolved fluorescence techniques it could be concluded that the observed fluorescence quenching was caused by a static interaction like a complex formation. While for phenanthrene both analytical methods showed no long term effects and the reaction equilibrium between NOM and phenanthrene was established within the first hour, for 9-aminophenanthrene a slow reaction kinetics (within days) was found indicating specific interactions between NOM and the amino group.
Determination of Am and Cm in spent nuclear fuels by isotope dilution inductively coupled plasma mass spectrometry and isotope dilution thermal ionization mass spectrometry after separation by high-performance liquid chromatography by Frédéric Chartier; Michel Aubert; Mireille Pilier (pp. 320-327).
Elemental and isotopic determination of americium and curium in spent nuclear fuels is necessary to validate neutronic calculation codes and for nuclear waste disposal purposes. Prior to mass spectrometric analysis, it is mandatory to perform separations in order to eliminate isobaric interferences between U, Pu, Am and Cm. In the spent fuels samples analyzed, a separation of U and Pu has been first realized with an anion-exchange resin. Then a rapid Am/Cm separation has been developed by high-performance liquid chromatography (HPLC) with an on-line detection using the Am and Cm α-emission. The influence of the different parameters on the chromatographic separation are described and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) and thermal-ionization mass spectrometry (TIMS) have been used to measure the isotopic composition of U, Am and Cm and to determine the 241Am/238U and 244Cm/238U ratios with the double spike isotope dilution method. The measurement procedures and the accuracy and precision of the results obtained with a quadrupole ICP-MS on different spent fuels samples are discussed and compared with those obtained by TIMS, used as a reference technique.
GC-MS determination and optimization of extraction of N,N′-dimethyl-N,N′-diphenylcarbamide from building materials by Á. Keszler; Béla Kazinczy; László Kótai (pp. 328-332).
N,N’-dimethyl-N,N’-diphenylcarbamide (centralite) extracted from building materials was quantitated using ion trap GC-MS detection technique. Both linearity and standard deviation of the calibration curve were dependent on the conditions of the mass spectral detection. The most precise calibration has been achieved by quantification of a mass ion not participating in secondary reactions and which is produced via single fragmentation. The best recovery of centralite was obtained after either 30 min of normal extraction with toluene at 60 °C or 10 min of ultrasonic extraction with chloroform at room temperature. Using the latter method resorption processes might cause decrease in efficiency of the recovery at longer extraction time.
A critical evaluation of the graphite furnace conditions for the direct determination of chromium in urine by S. P. Quináia; J. A. Nóbrega (pp. 333-337).
A critical study of the conditions for the direct determination of Cr in urine using GFAAS was carried out. A chemometric approach showed that the most important parameters that influence the efficiency of atomic Cr cloud formation were the atomization from the tube wall and the proper implementation of a pyrolysis step. The established procedure does not require any sample pre-treatment thus minimizing the risk of contamination. The Cr content in urine was determined using a calibration curve prepared with Cr spiked urine, easily correcting all potential matrix interferences. The heating program proposed took 68 s for a 30 μL urine sample. The procedure was applied for the determination of Cr in urine to investigate the absorption rate of Cr picolinate. The limit of detection and the characteristic mass for a 30 μL urine sample were 0.18 μg/L and 5.4 pg, respectively.
Multielement analysis of whole blood by high resolution inductively coupled plasma mass spectrometry by I. Rodushkin; Fredrik Ödman; Stefan Branth (pp. 338-346).
An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described. Sample preparation consisted of microwave digestion with nitric acid followed by dilution with ultrapure water. The importance of controlling possible contamination sources at different sample preparation and analysis stages in order to achieve adequate method detection limits (MDL) is emphasised. Correction for matrix effects was made using scandium, indium and lutecium as internal standards. Accuracy of the data for elements suffering from spectral interferences was improved by applying either a high resolution capability of the ICP-SMS or mathematical corrections. Different approaches for accuracy assessment in blood analysis are evaluated. Additional information on trace elements concentration in selected blood reference materials is given. The between-batch precision was assessed from replicate analysis (including sample preparation) of reference materials and was better than 10% RSD for 21 elements and better than 30% RSD for 36 elements under consideration. A statistical summary for results obtained for 31 blood samples from non-exposed subjects is presented. The majority of elements tested was found in the samples at concentrations higher than MDL.
Automated continuous monitoring of drug dissolution process using a flow injection on-line dialysis sampling – solvent extraction separation spectrophotometric system by Qun Fang; Yu-Qing Sun; Zhao-Lun Fang (pp. 347-352).
A flow injection (FI) system was developed incorporating on-line solvent extraction separation and stopped-flow dialysis systems for automated continuous monitoring of multi-vessel drug dissolution processes. The system employed PTFE pump tubes for solvent delivery, and combined a coaxial phase segmentor, conical cavity gravitational phase separator with a microdialysis sampling system to produce a reliable extraction system capable of stable non-stop operation over extended period of time. The system was evaluated for continuous monitoring in multi-vessel drug dissolution testing of ethambutol hydrochloride tablets using bromocresol green as reagent and chloroform as extractant. With the six-vessel dissolution system used, a sampling frequency of 15/h for each dissolution vessel was achieved with a total of 90 determinations per hour, giving an average precision of 3.6% RSD (n = 11). Results showed good agreement with those obtained using the Chinese Pharmacopoeia standard method.
Determination of total nitrogen in food by flow injection analysis (FIA) with a potentiometric differential detection system by José L. F. C. Lima; M. C. B. S. M. Montenegro; Ana P. M. M. O. Pinto (pp. 353-357).
A flow injection set-up based on potentiometric detection and gas diffusion device for the determination of total nitrogen in food is described. The detection system consisted of two ammonium-sensitive electrodes placed sequentially and each alternately operating as reference electrode. Tubular electrodes without an inner reference solution were prepared with a PVC membrane composed of nonactin in Tris (2-ethylhexyl) phosphate and potassium tetrakis (4-chlorophenyl) borate to reduce the membrane resistance. The food sample digests were inserted into the system, and the ammonium present was converted into ammonia gas. The gas diffused through a gas-permeable membrane to a buffer acceptor stream with a pH that ensured transformation to the ammonium cation, which was potentiometrically detected. Good agreement between FIA results and those provided by the reference procedure was obtained, with relative deviation errors below 5%. Using the proposed system, low reagent consumption is possible, a sampling rate of about 30 samples/h was achieved, as well as a good reproducibility for consecutive injections of the same sample (variation coefficient < 2%).
Determination of glucose in soft drink and sugar-cane juice employing a multicommutation approach in flow system and enzymatic reaction by Eloísa A. M. Kronka; Ana Paula S. Paim; B. F. Reis; José L. F. Costa Lima; Rui A. Lapa (pp. 358-361).
A flow system based on a multicommutation approach was developed for the determination of glucose and sucrose employing enzymatic reactions. The determination was based on the reaction with D-glucose generating hydrogen peroxide catalyzed by glucose-oxidase (GOD). Subsequently, the H2O2 generated reacts with 4-aminefenazone plus phenol to form 4-(p-benzoquinone-mono-imine) fenazone detected at 510 nm. This reaction is catalyzed by the peroxidase enzyme (POD). The flow network comprised a set of three-way solenoid valves and was controlled by means of a microcomputer furnished with an electronic interface and running a software written in Quick BASIC 4.5. The flow network and control software were designed to implement the multicommutation approach providing facilities to handle sample and reagent solutions, so that, sample dilution could be easily performed on line. Accuracy was assessed by comparison with results obtained by known procedures and no significant difference at the 95% confidence level was observed. Other advantageous features were a linear response ranging from 0.05 to 0.20% (w/v) glucose without prior dilution, a reagent consumption of 336 μL per determination, an analytical throughput of 30 samples per hour.
Determination of palladium in deoxo catalysts by differential pulse voltammetry by V. T. Aher; M. M. Palrecha; A. V. Kulkarni; G. C. Shah; P. K. Mathur (pp. 362-364).
A differential pulse voltammetric (DPV) method is proposed for the determination of palladium in deoxo catalysts, which are used in recombination units of the cover gas system of nuclear reactors. The electrode system consists of hanging mercury drop electrode (HMDE)/ platinum auxillary/ Ag-AgCl reference electrode. The supporting electrolyte consists of 0.02 M diammonium tartrate + 0.08 M ammonia-ammonium chloride buffer at pH 9.0. Fe, Cu, Pb, Ni, Co and Zn did not interfere. The interference by Cd could be eliminated using 0.005 M EDTA. The relative standard deviation of the proposed method was about 4.0% at ∼ 0.5% palladium content in the catalyst. The method is simple, rapid and free from any possible interferences.