Concentrations Of Mixture Components Research Articles

Use of QSAR models in predicting joint effects in multi-component mixtures of organic chemicals

The application of Quantitative Structure Activity Relationship (QSAR) models in predicting joint toxicity of mixtures of organic chemicals to microorganisms is presented. In the proposed approach, QSAR models derived from single chemical toxicity assays are used to predict concentrations of components in mixtures that would jointly cause 50% inhibition of microbial respiration. Experimental joint toxicity data from several different binary and multi-component, uniform and non-uniform mixture assays on two microbial cultures are used to validate the proposed approach. The predictions made from QSAR models agreed well with the experimental data with r 2=0.80 at p=0.0001 for a total of 610 data points. The factor of error of the predictions ranged from 1.00 to 4.79, averaging 1.82. Validation tests with 16 chemicals not used in the QSAR model derivation yielded predictions of similar quality.

Predicting Microbial Toxicity of Nonuniform Multicomponent Mixtures of Organic Chemicals

Three schemes proposed in the literature for analyzing joint toxic effects of multicomponent mixtures on fish, namely the additivity index (AI), the mixture toxicity index (MTI), and the similarity parameter (λ) are evaluated in this study for microbial toxicity. A new approach is proposed to establish acceptance limits for the similarity parameter, λ, based on experimental errors and uncertainties. Quantitative structure activity relationship (QSAR) techniques are then used to develop a model to predict the concentrations of components in mixtures that would jointly cause 50% inhibition of microbial respiration. The application of this approach is demonstrated on the experimental toxicity data of six eight-component organic chemical mixtures on microorganisms.

The investigation of Fe−Si alloys synthesized by laser irradiation

The results of structure and magnetic investigations of Fe−Si system alloys synthesized from iron and silicon powder mixture by laser irradiation are presented in this paper. It is established that a many-phased structure is formed in the alloys, the phase concentration of which depends on the concentration of mixture components. The concentration maxima of the phases formed in the alloys correspond to the stoichiometric values of the initial mixture composition. The nanocrystalline structure distinguished for its hyperparamagnetic properties is formed in the synthesized alloys.

Evidence for the temporal processing of odor mixtures in humans

The neural mechanisms underlying the perception of complex odor mixtures are largely unknown. The present study investigated the hypothesis that odorants in a mixture are processed and perceived in series. The results indicate that (i) odorants in mixtures are temporally processed with up to several hundred milliseconds separating individual components; (ii) ‘fast’ odorants are more likely to be a suppressor of ‘slow’ odorants than the reverse; and (iii) separation times can be altered by changing the concentrations of mixture components. These findings provide a new mechanism to account for the limited ability of humans to identify odorants in mixtures and for odor suppression.

Computer method for the simultaneous kinetic determination of compounds in mixtures based on the use of diode-array spectrophotometry

A computer method for the treatment of kinetic data provided by a diode-array spectrophotometer was developed. The method relies on a non-linear regression procedure for estimating the rate constants and concentrations of mixture components. The underlying principle of this method is fitting the absorption matrix obtained as a function of time and wavelength to a theoretical kinetic equation. This allows the resolution of mixtures of compounds with similar rate constants in a simultaneous fashion provided that they or their reaction products feature appreciable spectral differences from one another. The proposed method was applied to the resolution of Co(II) (0.1–1.0 μg ml −1)-Ni(II) (0.5–5.0 μg ml −1) mixtures based on displacement from their the EGTA complexes by 4-(2′-pyridylazo)resorcinol.

Theory of isothermal multicomponent sorption dynamics for high concentrations of mixture components

An analysis is made of the invariant solutions of the system of quasilinear equations of material balance which describe the motion of sorption shock and dispersing waves of concentration through a porous medium, when the flow velocity is variable (depending on the concentration of the components of a mixture of liquids or gases). It is shown that for linear sorption isotherms the problem formally reduces to one previously solved for a multicomponent system at constant flow velocity and Langmuir isotherms of the mixture. In the presence of dispersion factors and for linear sorption isotherms, solutions are obtained which describe the distributions of the concentrations in a traveling sorption wave regime.

Determination of component concentrations in mixtures of weak and strong acids and bases by linear algebraic methods

A general expression for transforming potentiometric titration curves of mixtures of weak acids into a system of linear equations is derived. The solution of the linear equations gives directly the concentrations of the components. This linear transformation method is illustrated by the analysis of mixtures of weak acids with overlapping dissociation equilibria. The possible presence of a strong acid or strong base in the mixture can also be detected and its concentration simultaneously determined. The method can also be used for analysis of an ampholyte and solutions containing a weak acid and its conjugate base. For example a mixture of hydroxyacetic acid (pK ∼ 3.6), acetic acid (pK ∼ 4.6) and hydroxylamine hydrochloride (pK ∼ 6) was analysed in the presence of strong acid with an average relative error of ∼2%.