On-line preconcentration of arsenic from water samples with an anion-exchanger column coupled to a hydride generation ICP system

Summary An on-line anion-exchange preconcentration hydride generation ICP system for the determination of total inorganic arsenic in water is described. The column was packed with strongly basic anion-exchange resin (AG 1-X8). Experimental conditions including pH of the sample solution, eluent, flow rate of eluent, oxidation states of arsenic and competing anion ions were studied. Compared with the conventional continuous hydride generation ICP, a 9.2-fold improvement in sensitivity was obtained with RSD 1–2% at 100 ng/ml. The detection limit (3) was 0.08 ng/ml. The recoveries in water samples were satisfactory. The system provides complete automation of sample loading, eluting and regenerating of the resin.On leave from Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai, China 200050     

The electronic structure of benzvalene : Photoelectronspectroscopic studies

The photoelectron(PE)spectrum of tricyclo[3.1.0.0^2,6] hex-2-ene(benzvalene 1) has been recorded. The first four bands in the PE spectrum of 1 can be assigned to transitions to ²B₂, ²A₁, ²A₂ and ²B₁ states of 1¹. This assignment is discussed in terms of the results of semiempirical and ab initio calculations on 1. Furthermore the highest occupied MO's of 1 are derived qualitatively from an interaction diagram between a distorted bicyclobutane and an ethylene moiety.     

Syntheses of 3,7-dimethylpentadecan-2-ols from intermediates formed from co-oligomerisation reactions of butadiene with diethyl malonate and acetaldehyde

The products of the reaction of butadiene with diethyl malonate catalysed by a palladium complex and of butadiene with acetaldehyde catalysed by a nickel(0) complex have been used in two syntheses of 3,7-dimethylpentadecan-2-ol.     

The determination of dissolved manganese and cadmium in sea water at low nmol 1−1 concentrations by chelation and extraction followed by electrothermal atomic absorption spectrometry

The development and application of a method suitable for the determination of dissolved manganese and cadmium in sea water at the low concentrations typical of the open ocean is described. A mixed dithiocarbamate/Freon TF extraction system is used to separate trace metals from major constituents, prior to back extraction into a final dilute nitric acid solution and subsequent determination of the metals by graphite-furnace atomic absorption spectrometry. The procedure also separates dissolved Co, Cu, Fe, Ni, Pb and Zn from a sea-water matrix. A mechanized system for the extraction step and measures to control contamination are described. The detection limits (3 σ) for manganese and cadmium are 0.10 and 0.04 nmol l^?1, respectively.     

Polymer blends—I. Mechanical and morphological behaviour of polyethylene/polyvinyl chloride blends

As part of a fundamental study of the behaviour of mixed plastics during reprocessing and in service, blends of low density polyethylene (LDPE) and polyvinyl chloride (PVC) have been investigated. It was found that Young's modulus increased steadily from pure LDPE to pure PVC whereas both tensile strength at break and elongation at break passed through a minimum at about 5% PVC. Optical and scanning electron microscope studies have related this mechanical behaviour to morphological changes in the two phase system under stress.     

Synthesis and antiinflammatory activity of the sulfoxides of 4-[3-(dimethylamino)propyl] - 3,4- dihydro- 2-(1-hydroxyethyl)-3-phenyl-2H-1,4-benzothiazine

Oxidation of 4-[3-(dimethylamino)propyl]-3,4-dihydro-2-(1-hydroxyethyl)-3-phenyl-2H-1,4-benzothiazine, hydrochloride (I) with hydrogen peroxide yielded a mixture of two sulfoxides (II). Since this mixture exhibited antiinflammatory activity, the two components (Isomers A and B) were prepared in purified form by oxidation of I with N-chlorosuccinimide and hydrogen peroxide, respectively. Isomer A was more potent than Isomer B in the carrageenin-induced edema test.     

Intramolecular hydroboration of unsaturated phosphine boranes

Homoallylic phosphine boranes undergo intramolecular hydroboration upon activation by triflic acid. The reaction occurs via an intermediate B-trifluorosulfonyloxyborane complex such as 15, followed by S(N)1-like or S(N)2-like displacement of the triflate leaving group, apparently leading to the formation of a four-center transition state. In the case of trisubstituted double bonds, as in the substrates 29 and 32, ionic hydrogenation of the alkene competes with internal hydroboration.     

Use of the mannich reaction in the synthesis of bispidine

A three-step synthesis of bispidine ( 1 ) is described. Mannich condensation of N-benzyl-4-piperidone, formaldehyde, and benzylamine afforded N,N′-dibenzylbispidinone ( 5 ), which was reduced under modified Wolff-Kishner conditions to yield N,N′ -dibenzylbispidine ( 6 ). Catalytic debenzylation of this compound gave 1 .     

On the dimerization of BH3 and the associated delocalization (resonance) energy

SCF calculations utilizing a basis of all s-type Gaussians have been performed to investigate the dimerization of BH₃ to B₂H₆. Localized molecular orbitals and pseudonatural orbitals are calculated. The dimerization energy obtained (11.5 kcal/mole) supports the assumption that the non-Hartree-Fock interactions (electron correlation) play a dominant role (Exp = 40–60 kcal/mole). The energy of the principal type of resonance structure based on the SCF-MO 's of the separated-but-distorted BH₃ systems is rigorously calculated and found to be 150 kcal/mole higher in energy than the SCF energy of B₂H₆. Thus, resonance stabilization (delocalization) is shown to be extremely important to the stability of the “three-center” bonds in B₂H₆, as has been suspected for many years.     

Optimization of a wet chemical continuous flow analysis method exemplified by the determinations of kjeldahl nitrogen and total phosphorus

The optimization of a rather complex wet chemical analysis method, such as the measurement of Kjeldahl nitrogen or total phosphorus with the Technicon AutoAnalyzer, is extremely tedious when purely empirical approaches are used. A mathematical model of the different stages of the measuring method (digestion, neutralization and color reaction) is described. The system can then be optimized for maximum measuring sensitivity. Optimization is done by solving numerically the non-linear optimization problem with constraints. The starting values for the optimization algorithm were found by varying these values systematically within the tolerated range, with checks that none of the constraints were violated. The theoretical results predict an increase in sensitivity by a factor of 15 compared to the method used previously. In practice, the sensitivity was increased by a factor of 10 for the total phosphorus method. For the simultaneous low-level determinations of Kjeldahl nitrogen and total phosphorus some problems of stability remain.