Analytical quality control for the determination of polychlorobiphenyls in environmental matrices

Analytical quality control procedures for ensuring reliable data in the determination of PCBs in environmental matrices are described. Several extraction procedures of PCBs from sediment samples are critically compared and recovery and reproducibility for PCBs determination in sediment and cod liver oil samples are evaluated. Extraction by 1:1n-hexane/acetone mixture in an ultrasonic bath and by supercritical fluids generally give a quantitative recovery and a coefficient of variation lower than 15%, while extraction by a Soxhlet system does not give such good results and requires much longer extraction times. Certified reference materials available from three international organizations, namely the Standards, Measurements and Testing programme of the European Union, the USA National Institute of Standards and Technology and the National Research Council of Canada were used. Finally, the on-going European Union QUASIMEME programme aimed at improving the analytical quality of marine pollution monitoring measurements of European laboratories is addressed.     

Chromatographic behaviour of selected steroids and their inclusion complexes with beta-cyclodextrin on octadecylsilica stationary phases with different carbon loads

Retention and separation studies of selected estrogens, progestogens and their inclusion complexes with beta-cyclodextrin were conducted using two C18 HPLC columns with different carbon loads. The difference in carbon load between investigated octadecylsilica packing materials was about 50%. The mobile phases were composed of a 30% v/v acetonitrile-water mixture without and with addition of beta-cyclodextrin at a concentration of 12 mM. The experimental data revealed that retention of the steroids was significantly reduced on the column with the lower carbon load. Moreover, it was found that this column offers better separation power and shorter analysis time at the temperatures studied. However, the calculated values of the retention factor ratios (k0(mMCD))/k(12mMCD)) of the steroids were similar for both columns investigated. This observation suggests that the stationary phase structure appears to have little effect on the formation of host-guest complexes if the complexation process is localised to the chromatographic mobile phase. From a practical point of view, when the mobile phase is modified with beta-cyclodextrin, the separation of the steroids is strongly influenced by temperature. The best chromatographic conditions were determined for the separation of multicomponent samples on the column with lower carbon load. A possible retention mechanism for components of interest in the presence of macrocyclic additives is discussed.     

Synthesis of fluorous acetal derivatives of aldehydes and ketones

The formation of acetals (and ketals) from polyfluoroalkylated 1,3-alkanediols and aldehydes and ketones is demonstrated for the first time. Four sets of reaction conditions are examined and the degree of conversion is shown to depend upon reaction conditions and the structure of the carbonyl substrate. Excellent yields are obtained, and wherever possible, diastereomeric products are observed.     

Deux types de participation π lors de l'hydrolyse des diazocétones γ, δ-insaturées par des acides aqueux et des superacides. L'ion oxo-5-norbornyle-2

γ, δ-Unsaturated diazoketones undergo acid catalysed hydrolysis accompanied by cyclisation; the latter is favoured by suitable geometry (cyclopentenes) and by substitution by methyl groups. If both are present, rate enhancement by anchimeric assistance has been observed. Hydrolysis of 4-diazoacetyl-cyclopentene ( 1 ) yields a product mixture similar to that formed during solvolysis of 5-oxo-norbornyl-2-endo brosylate (23) and quite different from that of the exo isomer. The results are interpreted in terms of a common intermediate, the 5-oxo-2-norbornyl carbonium ion. Solvent participation in the transition state, i. e. partial S_N 2 character, is implied by the entropies of activation and by the action of an added nucleophile (Br^?). In superstrong acids, a different type of cyclisation takes place, involving the carbonyl oxygen and the protonated C? C double bond and forming tetrahydropyrane derivatives.     

Osmotic coefficients and activity coefficients of aqueous hydrobromic acid solutions at 25°C

The osmotic coefficients ? and activity coefficients γ_± of aqueous solutions of HBr depend largely on emf measurements utilizing the silver-silver bromide electrode. There is evidence, however, that side reactions between AgBr and bromide ion render this electrode unreliable when the HBr molality (m) exceeds 2 mol-kg^?1. It is shown, however, that the isopiestic vapor-pressure technique is capable of yielding data for HBr at higher molalities. New emf measurements of cells with hydrogen and AgBr/Ag electrodes at 25°C have been combined with literature data to recommend values for the activity coefficients of HBr in the dilute range. These have been supplemented by isopiestic measurements vs. NaCl and CaCl₂ reference solutions in the range of HBr molalities from 0.7 to 6.2m. A table of ? and γ_± at 25°C at round molalities from 0.005 to 6.0 is presented.     

Comparison of experimental and calculated peak shapes for three cylindrical geometry FAIMS prototypes of differing electrode diameters

High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates ions at atmospheric pressure and room temperature based on the difference of the mobility of ions in strong electric fields and weak electric fields. This field-dependent mobility of an ion is reflected in the compensation voltage (CV) at which the ion is transmitted through FAIMS, at a given asymmetric waveform dispersion voltage (DV). Experimental CV, relative peak ion intensity, and peak width data were compared for three FAIMS prototypes with concentric cylindrical electrodes having inner/outer electrode radii of: (1) 0.4/0.6 cm, (2) 0.8/1.0 cm, and (3) 1.2/1.4 cm. The annular analyzer space was 0.2 cm wide in each case. A finite-difference numerical computation method is described for evaluation of peak shapes and widths in a CV spectrum collected using cylindrical geometry FAIMS devices. Simulation of the radial distribution of the ion density in the FAIMS analyzer is based upon calculation of diffusion, electric fields, and the electric fields introduced by coulombic ion-ion repulsion. Excellent agreement between experimental and calculated peak shapes were obtained for electrodes of wide diameter and for ions transmitted at low CV.     

Two-stage application of the optimised uncertainty method: a practical assessment

Uncertainty estimates from routine sampling and analytical procedures can be assessed as being fit for purpose using the optimised uncertainty (OU) method. The OU method recommends an optimal level of uncertainty that should be reached in order to minimise the expected financial loss, given a misclassification of a batch as a result of the uncertainty. Sampling theory can used as a predictive tool when a change in sampling uncertainty is recommended by the OU method. The OU methodology has been applied iteratively for the first time using a case study of wholesale butter and the determination of five quality indicators (moisture, fat, solids-not-fat (SNF), peroxide value (PV) and free fatty acid (FFA)). The sampling uncertainty (s(samp)) was found to be sub-optimal for moisture and PV determination, for 3-fold composite samples. A revised sampling protocol was devised using Gy's sampling theory. It was predicted that an increase in sample mass would reduce the sampling uncertainty to the optimal level, resulting in a saving in expectation of loss of over pounds 2000 per 20 tonne batch, when compared to current methods. Application of the optimal protocol did not however, achieve the desired reduction in s(samp) due to limitations in sampling theory. The OU methodology proved to be a useful tool in identifying broad weaknesses within a routine protocol and assessing fitness for purpose. However, the successful routine application of sampling theory, as part of the optimisation process, requires substantial prior knowledge of the sampling target.     

Reduced rings whose finitely generated modules decompose

This paper proves Hua's Theorem and, from this, the Fundamental Theorem of Projective Geometry for the projective line over a commutative ring with “many units”.     

Pontryagin’s principle for state-constrained evolutionary differential complementarity system

This paper is devoted to the state-constrained optimal control problem of evolutionary variational inequality. In this paper, the control domain is not necessarily convex. Moreover, since our state constraint is quite general and, in many cases, it requires pointwise behavior of the state, the framework of the partial differential equation (instead of the abstract framework) is used. Some optimality conditions (in the form of Pontryagin’s principle) for optimal controls are established.