Determination of aluminium in the edible part of fish by GFAAS after sample pretreatment with microwave activated oxygen plasma

An analytical method for the determination of aluminium in the edible part of fish was developed using a new pre-treatment method in a microwave activated oxygen plasma and graphite furnace atomic absorption spectrometry. The linearity of the calibration line as well as of different standard addition lines were very good within the measurement area of 0–60 μg Al/L. The recovery with spiked ocean perch fillet was good. The unsatisfactory recovery of aluminium with the reference-material (mussel tissue) may be due to high quantities of insoluble aluminium-silicates. An installed quality-control-card indicated that the method showed no significant fluctuation as well as contamination over the complete analysis time. The limit of detection calculated as 3 times the standard deviation of the blank absorbance divided by the slope of the calibration line was 1 μg Al/L. Received: 7 December 1998 / Revised: 14 February 1999 / Accepted: 24 February 1999     

Determination of aluminium in the edible part of fish by GFAAS after sample pretreatment with microwave activated oxygen plasma

An analytical method for the determination of aluminium in the edible part of fish was developed using a new pre-treatment method in a microwave activated oxygen plasma and graphite furnace atomic absorption spectrometry. The linearity of the calibration line as well as of different standard addition lines were very good within the measurement area of 0–60 μg Al/L. The recovery with spiked ocean perch fillet was good. The unsatisfactory recovery of aluminium with the reference-material (mussel tissue) may be due to high quantities of insoluble aluminium-silicates. An installed quality-control-card indicated that the method showed no significant fluctuation as well as contamination over the complete analysis time. The limit of detection calculated as 3 times the standard deviation of the blank absorbance divided by the slope of the calibration line was 1 μg Al/L. Received: 7 December 1998 / Revised: 14 February 1999 / Accepted: 24 February 1999     

An electrochemical method for quantification of the radical scavenging activity of SOD

An electrochemical technique for the determination of enzymatic superoxide scavenging activity is described. In amperometric mode of sensor operation ?the oxidation current was altered by additions of superoxide dismutase (SOD). The 50% inhibition value (I50) corresponded to 0.165 U of the standard photometric test of McCord and Fridovich. Influence by inert proteins was much less than in the standard method: The SOD/BSA ratio was 4 × 10⁵. Potentially interfering substances, e.g. ascorbic acid and glutathione, were tested. Plasma samples of rats which were treated with modified SOD during cerebral ischaemia, were assayed with the new method and the standard photometric test. A good correlation was found for the analysis in these physiological samples (r = 0.97). Received: 3 February 1999 / Revised: 17 May 1999 / Accepted: 19 May 1999     

In situ doping polymerization of polyaniline microtubules in the presence of β‐naphthalenesulfonic acid

Conducting microtubules of Polyaniline (PANI) were synthesized for the first time by the “in situ doping polymerization” method in the presence of β‐naphthal‐ enesulfonic acid (NSA) as dopant. Different doping methods, such as “immerse doping” and “grind doping,” and different synthetic conditions, such as molar ratio of aniline (An) to NSA (An/NSA), concentration of NSA in the polymerization media, reaction temperature, and time were investigated to understand the formation of microtubules. It was found that the PANI–NSA microtubules can be formed only by the “in situ doping polymerization” method, and the above synthetic conditions strongly affect the formation of the PANI–NSA microtubules, especially the molar ratio of An to NSA. An optimal condition was found under which tubules with 1–3 μm in diameter and 10–50 μm in length were obtained. The morphology of PANI–NSA tubules was proved by SEM and TEM, and their backbone structure was characterized by FTIR, UV‐VIS, XPS, and X‐ray diffraction. Results of these measurements showed that the molecular structures of the resulted PANI–NSA microtubules were identical to that of PANI–HCl synthesized by conventional method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 151–157, 1999     

Solar blind photocell – a simple element specific detector in Hg, As and Se speciation

An element-specific detection method, based on atomic absorption spectrometry (AAS) using solar blind photocells instead of a dispersion system, is described for the determination of Hg-, As-, and Se-species. Spectrometric investigations of AAS background lamps for As and Se measured with a CsI-cathode photocell shows its quality as narrow band detector. Species determination can be carried out subsequently to prior separation by HPLC or GC. The LODs for alkylated Hg species were below 1 ng/L, and for methylated As species below 1 μg/L. The relative standard deviation was < 10%. With the components described the production of cheap and automated dedicated speciation spectrometers is possible. Received: 18 May 1999 / Revised: 6 September 1999 / Accepted: 13 September 1999     

Implementation of atomic basis set composed of 1s Gaussian and 1s Slater-type orbitals to carry out quantum mechanics molecular calculations

A mixed atomic basis set formed with ls Slater-type orbitals and 1s floating spherical Gaussian orbitals is implemented. Evaluation of multicenter integrals is carried out using a method based on expansion of binary products of atomic basis functions in terms of a complete basis set, and a systematic analysis is performed. The proposed algorithm is very stable and furnishes fairly good results for total energy and geometry. An LCAO-SCF test calculation is carried out on LiH. The trends observed show that there are some combinations of mixed orbitals that are appropriate to describe the system. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 604–609, 1999     

Using simplified protein representation as a reference potential for all-atom calculations of folding free energy

An effective approach for evaluating folding free-energy surfaces of explicit all-atom models is developed and examined. This approach is based on using the potential of a simplified protein model as a reference potential for calculating the free energy of the corresponding explicit model. Preliminary results are presented for the folding free energy of a 12-residue helix. The potential of the method for studies of protein-folding processes is discussed, emphasizing the ability to determine the difference between the results of simplified and explicit models. This can help in establishing the validity of simplified folding models. Received: 30 December 1998 / Accepted: 27 January 1999 / Published online: 5 May 1999     

Assessment of permissible ranges for results of pH-metric acid number determinations using uncertainty calculation

 An approach to assess the permissible ranges for results of replicate determinations using uncertainty calculation is discussed. The approach is based on the known range distribution for normalized "range/standard deviation" values, which is equivalent to the distribution of the range for normalized results of replicate determinations having an average of 0 and a standard deviation of 1. It is shown that the permissible ranges can be assessed using tabulated percentiles of this distribution and calculated values of the determination (analysis) standard uncertainty. When the standard uncertainty calculation is performed before the analytical method validation, the permissible ranges can be predicted. As an example, the range is predicted for a new pH-metric method for acid number determination without titration in petroleum oils (basic, white and transformer). The results of the prediction are in good conformity with the experimental data. Received: 23 May 1999 · Accepted: 14 November 1999     

Trace analysis of pentachlorophenol (PCP) in wood and wood-based products – comparison of sample preparation procedures

The main problem with routine analyses of pentachlorophenol (PCP) and sodium pentachlorophenolate (Na-PCP) in wood and wood-based products is to determine critical PCP-contents. This task requires a reliable analytical method and statistical testing. An analytical procedure is described, which permits the determination of PCP and Na-PCP with sufficient sensitivity and accuracy. A medium size sieve (4 × 4 mm quadratic mesh) was found suitable for the grinding step. Different extraction techniques and solvents were tested systematically. Extraction by a combination of ultrasonication and shaking in the solvent mixture toluene/sulfuric acid showed best recoveries. The eluted PCP and Na-PCP were derivatized with acetic anhydride and determined by GC/ECD. The limits of detection and determination were 0.14 mg/kg and 0.40 mg/kg, respectively. Received: 6 August 1999 / Revised: 26 October 1999 / Accepted: 1 November 1999     

Enzymatic polymerization: A new method of polymer synthesis

Enzymatic polymerization denotes an in vitro polymerization via nonbiosynthetic pathways catalyzed by an isolated enzyme. This article describes the recent progress of this polymerization technique, developed mainly during this decade. The polymerization utilizes enzymes of hydrolases and oxidoreductases as catalysts. This new method of polymer synthesis provided natural polysaccharides like cellulose, amylose, xylan, and chitin, and unnatural polysaccharides catalyzed by a glycosidase from well-designed monomers, various functionalized polyesters catalyzed by lipase from a variety of monomers, and polyaromatics materials catalyzed by an oxidoreductase and an enzyme model complex from phenols and anilines. An oxidoreductase also initiated vinyl polymerizations. Characteristic features of enzymatic polymerizations are discussed, including the importance of the combination of substrate monomer and enzyme. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3041–3056, 1999     

Ab initio compact group model potentials for describing environment effects in cluster calculations

A method for the determination of ab initio group model potentials within the Hartree–Fock framework is reported. Following the theory of separability of many electron systems, a new way to incorporate the effect of complete chemical entities by means of polycenter compact model potentials is presented. The interaction between active and frozen electrons is partitioned as a sum of long- and short-range terms. The long-range term is described as the effect of −2e charges placed in the center of the charge of the frozen group molecular orbitals; the short-range one, the exchange and Pauli repulsion, is developed as a spectral representation in a nonorthogonal basis set. An algorithm to solve the problem associated with the rotation of the polycenter model potential is presented and implemented in an all-purpose quantum chemical program. In order to check the method, a group model potential for H₂O was obtained and tested. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1145–1152, 1999     

Efficient calculation of short-range Coulomb energies

An efficient algorithm for the calculation of short-range Coulomb energies is examined. The algorithm uses a boxing scheme and a prescreening for negligible integrals to evaluate the short-range Coulomb energy via computational work that scales only linearly with the size of the system. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 921–927, 1999     

Analysis of the relaxations on polymers from the real part of a general complex susceptibility. Application to dielectric relaxations

From a thermodynamic relation that involves the generalized relaxation function, an approximated method that allows estimation of the thermal dependence of the imaginary part of the general complex susceptibility from the real part is discussed. Several conditions such as broad distribution of relaxation times, the applicability of the time–temperature superposition principle, and the temperature dependence of the relaxation strength are considered and analyzed, together with the expected thermal behavior of the relaxed and unrelaxed susceptibilities. The method is tested by means of dielectric measurements on the poly(vinyl acetate) polymer in the temperature range corresponding to the segmental dynamics and the secondary relaxation. An acceptable agreement respect with the maximum temperature of the ε″(T) and the width and shape of the loss peak is obtained between the experimental and estimated imaginary part. This comparison gives validity to the method when the imaginary part is experimentally not well resolved due to the signal–resolution ratio or to the presence of other contributions that mask the thermal behavior of the imaginary part. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1337–1349, 1999     

Complexometric Determination of Zinc(II) Using 2,2′-Bipyridyl as Selective Masking Agent

 An indirect complexometric method is described for the determination of zinc(II) using 2,2′-bipyridyl as masking agent. Zinc(II) in a given sample solution is initially complexed with an excess of EDTA and surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamine), using xylenol orange as indicator. An excess of 2,2′-bipyridyl is then added, the mixture shaken well and the EDTA released from the Zn-EDTA complex is titrated with standard lead nitrate solution. Results are obtained for 3–39 mg of Zn with relative errors ≤ 0.5% and standard deviations ± 0.06 mg. The interference of various ions are studied. The method is applied for the determination of zinc in its alloys and ores. Received October 27, 1998. Revision June 10, 1999.     

Synthesis and structure of anhydroindanone‐1 disulfide

An unexpectedly high yield of anhydroindanone‐1 disulfide (1) was obtained by reaction of Lawesson's reagent with indanone‐1. The molecular structure of 1 was established by X‐ray diffraction. A possible mechanism of the reaction is discussed. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 369–371, 1999     

Determination of trace metals in high purity gold

The possibility of using ETAAS or ICP-AES for the determination of trace amounts of Ag, Bi, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Pd, Pt and Sb in pure gold is investigated. The influence of the matrix element on the atomization of the trace analytes is studied and optimal instrumental parameters are defined. An analytical method based on matrix element reductive separation followed by spectrometric determination of trace analytes is proposed as an alternative for the analysis of high purity gold. Advantages and disadvantages of proposed analytical procedures from the viewpoint of achieved repeatability, reproducibility and detection limits and of the duration of analysis are discussed. Received: 16 August 1999 / Revised: 23 November 1999 / Accepted: 27 November 1999     

Fluorodesulfurization of aliphatic orthothioesters

In contrast with aromatic orthothio esters that undergo desulfurative fluorination to produce trifluoromethyl substituted aromatics, aliphatic orthothio esters react with BrF with replacement of only one or two methylthio groups by fluorine. An elimination step often follows the first sulfur replacement to produce novel unsaturated fluorinated systems. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 31–34, 1999     

Laser ablation-atomic fluorescence approach for the determination of mercury

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. Received: 21 December 1998 / Revised: 12 April 1999 / Accepted: 14 April 1999     

Consistent modifications of SINDO1: I. Approximations and parameters

A consistent modification, MSINDO, of the semiempirical MO method SINDO1 is presented. Different basis sets are used for one- and two-center interactions. The treatment of the core matrix elements in the nonorthogonal basis is retained with changes only for hydrogen and 3d orbitals. Orthogonalization corrections are now restricted to nonvanishing core matrix elements in the INDO approximation. The set of atomic parameters is increased, but bond parameters are no longer used. An automatic nonlinear least-squares algorithm with a restricted step constraint is used for the optimization of parameters. Heats of formation are adjusted with inclusion of zero-point energies obtained by a scaling procedure of the force constant matrix. The present version MSINDO provides significant improvements over previous versions. A brief comparison for ground-state properties of the elements H, C, N, O, F, and Na to Cl is given. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 563–571, 1999