Esther Forgács

Biological activity and environmental impact of anionic surfactants.

The newest results concerning the biological activity and environmental fate of anionic surfactants are collected and critically evaluated. The chemical and physicochemical parameters related to the biological activity and the field of application are briefly discussed. Examples on the effect of anionic surfactants on the cell membranes, on the activity of enzymes, on the binding to various proteins and to other cell components and on their human toxicity are presented and the possible mode of action is elucidated. The sources of environmental pollution caused by anionic surfactants are listed and the methods developed for their removal from liquid, semiliquid and solid matrices are collected. Both the beneficial and adversary effects of anionic surfactants on the environment are reported and critically discussed. It was concluded that the role of anionic surfactants in the environment is ambiguous: they can cause serous environmental pollution with toxic effect on living organisms; otherwise, they can promote the decomposition and/or removal of other inorganic and organic pollutants from the environment. The relationship between their chemical structure, physicochemical parameters, biological activity and environmental impact is notwell understood. A considerable number of data are needed for the development of new anionic surfactants and for the successful application of the existing ones to reduce the adversary and to promote beneficial effects.

Comparative analysis of different plant oils by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

Different vegetable oil samples (almond, avocado, corngerm, grapeseed, linseed, olive, peanut, pumpkin seed, soybean, sunflower, walnut, wheatgerm) were analyzed using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. A gradient elution technique was applied using acetone-acetonitrile eluent systems on an ODS column (Purospher, RP-18e, 125 x 4 mm, 5 microm). Identification of triacylglycerols (TAGs) was based on the pseudomolecular ion [M+1]+ and the diacylglycerol fragments. The positional isomers of triacylglycerol were identified from the relative intensities of the [M-RCO2]+ fragments. Linear discriminant analysis (LDA) as a common multivariate mathematical-statistical calculation was successfully used to distinguish the oils based on their TAG composition. LDA showed that 97.6% of the samples were classified correctly.

Optimisation of the microwave-assisted extraction of pigments from paprika (Capsicum annuum L.) powders

The efficiency of microwave-assisted extraction (MAE) for the extraction of colour pigments from paprika (Capsicum annuum) powders was evaluated using 30 extracting solvent mixtures. The separation efficacy and selectivity of MAE was carried out using a spectral mapping technique and the relationship between the efficacy and selectivity of extraction and the physicochemical parameters of solvent mixtures was calculated by stepwise regression analysis. The calculation results were verified experimentally by the separation of pigment fractions by high-performance liquid chromatography. It was established that both the efficacy and selectivity of MAE depend significantly on the dielectric constant of the extraction solvent mixture.

Retention characteristics and practical applications of carbon sorbents

Reversed-phase separations provides a versatile technique in high-performance liquid chromatography. Porous graphitized carbon (PGC) support shows unique retention characteristics. Separations on PGC columns use typical reversed-phase eluents (water and organic modifiers miscible with water), however, the retention order of solutes generally does not follow their hydrophobicity order. Molecular hydrophobicity influences but not determines the elution order of any set of solutes. The properties of these supports, mechanisms of retention and application are discussed, along with correlations which can guide the choice of solvent combinations for typical separations.

Phenoxyacetic acids : separation and quantitative determination

The various chromatographic methods suitable for the separation and quantitative determination of phenoxyalkyl acid herbicides in environmental samples are reviewed, with special emphasis being placed on sample preparation methods such as liquid-liquid, solid-phase and supercritical fluid extractions. Techniques are classified (high-performance liquid chromatography, gas-liquid chromatography, capillary zone electrophoresis, micellar electrokinetic chromatography) and discussed separately. The advantages and disadvantages of the various preparation and separation methods and their combinations are evaluated.

Polyethylene-coated silica and zirconia stationary phases in view of quantitative structure-retention relationships

SummaryRetention properties of two new high-performance liquid chromatographic (HPLC) stationary phases, polyethylene-coated silica (PECSiO2) and polyethylene-coated zirconia (PECZrO2), were compared chemometrically. Reversed phase HPLC capacity factors were determined isocratically for a carefully designed series of 25 structurally diverse solutes. Linear free energy relationship (LFER)-based solute parameters (excess molar refraction, dipolarity-polarizability, hydrogen-bond acidity and basicity, McGowan volume) and solute structural descriptors determined by physico-chemical methods (water accessible van der Waals volume, dipole moment, atomic electron excess charge) were regressed as independent variables against log capacity factors. The quantitative structure-retention relationships (QSRR) obtained show the predominating partition mechanism of separation on both phases. Both the LFER parameters and the structural parameters obtained by molecular modelling produced QSRR equations of high and practically identical retention prediction ability. It has been concluded that intermolecular interactions of the dipolarity-polarizability type manifest themselves more strongly on the silica-based phase than on the zirconia-based one. This can be due to a role of active free silanols on the silica support.

Influence of storage conditions on the stability of monomeric anthocyanins studied by reversed-phase high-performance liquid chromatography

The effect of light, storage time and temperature on the decomposition rate of monomeric anthocyanin pigments extracted from skins of grape (Vitis vinifera var. Red globe) was determined by reversed-phase high-performance liquid chromatography (RP-HPLC). The impact of various storage conditions on the pigment stability was assessed by stepwise regression analysis. RP-HPLC separated well the five anthocyanins identified and proved the presence of other unidentified pigments at lower concentrations. Stepwise regression analysis confirmed that the overall decomposition rate of monomeric anthocyanins, peonidin-3-glucoside and malvidin-3-glucoside significantly depended on the time and temperature of storage, the effect of storage time being the most important. The presence or absence of light exerted a negligible impact on the decomposition rate.

Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns

SummaryThe retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH2PO4 mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.

Retention behaviour of some ring-substituted phenol derivatives on a porous graphitized carbon column

Abstract The retentions of 24 ring-substituted phenol derivatives were determined on a graphitized carbon column using unbuffered acetonitrile-water and methanol-water eluent mixtures at various organic phase concentrations. Principal component analysis calculated from both the correlation and covariance matrices was used to detect the similarities and dissimilarities between the retention behaviours of phenol derivatives. Each phenol derivative showed narrow and symmetrical peaks in each eluent. The high percentage of variance explained in the first principal component suggests that the eluents have common elution characteristics; however, according to the second principal component they showed slightly different selectivities. Calculations demonstrated that the number and not the type of substituents exerts the highest impact on the retention. Both calculation methods (based on correlation and covariance matrices) gave similar results.

Determination of the retention behavior of barbituric acid derivatives in reversed-phase high-performance liquid chromatography by using quantitative structure–retention relationships

Retention parameters of 45 barbituric acid derivatives were determined on an amide embedded RP silica column using non-buffered water-dioxan eluent systems. Linear correlations were calculated between the logarithm of the capacity factor and the dioxan concentration in the eluent. Six different retention parameters of each barbituric acid derivative were correlated with different conventional and quantum chemical structural descriptors using quantitative structure-retention relationship (QSRR). The different parameters were: intercept (log k0) and slope (b) values of the linear, the combined retention parameter (log k0/b), asymmetry factor (AF5) and theoretical plate values (N(USP) and N(JP), according to the United States and Japanese Pharmacopoeia calculations). Stepwise regression analysis (SRA) and principal component analysis (PCA) followed by two-dimensional nonlinear mapping were used to determine the retention behavior of barbituric acid derivatives. SRA and PCA led to similar results. The results indicated that the retention of barbituric acid derivatives are mainly governed by the polaric and steric parameters of the substituents.