Nitrous Oxide as Carrier Gas in Capillary Gas-Liquid Chromatography

On use of nitrous oxide as carrier gas the retention factors of the chromatographed compounds decrease linearly with increasing average column pressure. Other retention characteristics (relative retention, retention index) change linearly. This effect was demonstrated by using a capillary column coated with nonpolar polydimethylsiloxane phase SE-30. As shown for capillary GLC the linear correlation is valid for the same column:k_i(G₁,P₁) = A k_i(G₂, P₂) + B, where k_i(G₁, P₁) and k_i(G₂,P₂) are the retention factors of compound i at average column pressures P₁ and P₂ when using carrier gases G₁ and G₂, respectively; A and B are coefficients.     

Preconcentration of heavy metal impurities from water on chromatographic paper

An attempt is made to employ the previously proposed method for preconcentration of nonvolatile impurities as a narrow zone on a TLC plate or on chromatographic paper for extraction of heavy metals from potable water. The method is based on vigorous evaporation of a volatile matrix (water) induced by a stream of hot air. The degree of preconcentration was determined using ICP MS analysis for lead, cobalt, and zinc. The concentrations of impurities increased by a factor of more than 200 over a period of 20–30 min. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1399–1400, August, 2000.     

Electrochemical synthesis of substituted trialkyl phosphates

The process of synthesis of tryalkyl phosphates, i.e., derivatives of methanol, butanol, and diethylene glycol, by anodic oxidation of dimethyl phosphite in the corresponding alcohol is studied. It is found that three alkyl phosphates corresponding to the three possible combinations of substituents bound to phosphorus in phosphate are formed. It is established that the cause for formation of two of the three oxidation products is reesterification of the initial dimethyl phosphite by the alcohol in the course of electrolysis. It is assumed that the process of reesterification is catalyzed by the acid formed in the anode layer.     

Theoretical Study of Twin Polymerization – From Chemical Reactivity to Structure Formation

Twin polymerization is a novel technique for synthesizing hybrid polymers with domain sizes in the nanometer range. While a broad variety of monomers have been investigated, the mechanistic details and the most important influences on the nanostructure formation are unknown. A scale bridging approach is presented to simulate the twin polymerization of 2,2'‐spirobi[4H‐1,3,2‐benzodioxasiline]. This approach is based on detailed quantum chemical calculations that yield insight into reactivity and structure at the molecular level while the kinetics of the network formation process and the influences that govern structure formation are investigated at the mesoscopic level by a coarse‐grained simulation.

     

Convergence analysis of two-phase methods for approximating the Edgeworth-Pareto hull in nonlinear multicriteria optimization problems

The convergence of two-phase methods for approximating the Edgeworth-Pareto hull (EPH) in nonlinear multicriteria optimization problems is analyzed. The methods are based on the iterative supplement of the finite set of feasible criteria vectors (approximation basis) whose EPH approximates the desired set. A feature of two-phase methods is that the criteria images of randomly generated points of the decision space approach the Pareto frontier via local optimization of adaptively chosen convolutions of criteria. The convergence of two-phase methods is proved for both an abstract form of the algorithm and for a two-phase method based on the Germeier convolution.     

Some features of thin-layer chromatography in chambers of different types

The following characteristics of planar chromatography in the ascending flow of the mobile phase were compared for the main N, S, and O chambers: the movement of the mobile phase front, the efficiency of the chromatographic process, and the retardation factors. The optimum results were obtained for S and O chambers.     

Quasi-Continuous Videodensitometric Recording of Chromatograms in Circular TLC

JPC – Journal of Planar Chromatography – Modern TLC - A new method of quasi-continuous videodensitometric recording of circular thin-layer chromatography (TLC) is proposed. It is based...     

Study of hybrid methods for approximating the Edgeworth-Pareto hull in nonlinear multicriteria optimization problems

Methods for approximating the Edgeworth-Pareto hull (EPH) of the set of feasible criteria vectors in nonlinear multicriteria optimization problems are examined. The relative efficiency of two EPH approximation methods based on classical methods of searching for local extrema of convolutions of criteria is experimentally studied for a large-scale applied problem (with several hundred variables). A hybrid EPH approximation method combining classical and genetic approximation methods is considered.