C. Bighi

Evaluation of the number of components in multi-component liquid chromatograms of plant extracts

Optimization of the chromatographic separation of flavonoid compounds in camomile extracts by the simplex method and the Monte Carlo method is described. Evaluation fo the number of peaks at unit resolution (Rs = 1) is used as the criterion of separation quality. The Davis-Giddings theory is applied in calculating the number of components and the results are validated by numerical simulations. Peak-purity checks for three identified compounds in commercial sample extracts are reported. Capacity factor patterns for 18 flavonoid and phenolic compounds over an extended range of methanol/aqueous buffer (pH 2.8) mobile phases are described.

Characterization of some styrene-divinylbenzene sorbents for reversed-phase chromatography

Abstract The preparation and characterization of laboratory made polymeric columns of Chromosorb 101 and Porapak Q are described, with reference to a PRP-1 column packed under the same conditions. Column parameters such as permeability, efficiency and peak asymmetry factor were calculated. The swelling propensity of the materials was measured and the dependence of peak shape on the type of organic solvent used was investigated. The efficiencies of Chromosorb 101 and Porapak Q columns were satisfactory but the spherical material PRP-1 gave better results. Porapak Q exhibited very good physical properties such as high rigidity and permeability. The swelding of polymers in acetonitrile is higher than in methanol, so a better column performance is obtained when acetonitrile is employed as the eluent.

High-performance liquid chromatographic determination of naphthols as 4-aminoantipyrine derivatives : Application to carbaryl

Abstract The high-performance liquid chromatographic determination of 1- and 2-naphthol after derivatization with 4-aminoantipyrine is described. The chromatographic analysis of the reaction mixtures showed two main coloured products for each naphthol. In order to investigate the nature of the reaction products a spectroscopic study ( UV — VIS , IR , NMR ) of the products separated by chromatography was performed. On the more stable 1-naphthol reaction product the quantitative determination of 1-naphthol was performed in the 0.05–10 ppm concentration range. Instability of the 2-naphthol products made their quantitative determination difficult; detection at two different wavelengths (460 and 412 nm) gave a very reliable criterion of qualitative identification. As 1-naphthol is the major degradation product of the insecticide carbaryl, this determination reaction of 1-naphthol was applied to carbaryl. The applicability and performance of the method was checked by determining the carbaryl content in commercial powder formulations and residues in apples.

Determination of phenols in water samples as 4-aminoantipyrine derivatives by high-performance liquid chromatography

Abstract The determination of 22 monohydric phenols by high-performance liquid chromatography after derivatization with 4-aminoantipyrine is described. The reaction variables were evaluated in order to examine the performance of the method at low ppb★ concentrations. The chromatographic behaviour of the derivatives was investigated by carrying out separations on different bonded-phase columns, which provided a satisfactory selectivity under isocratic elution conditions. Separations of complex mixture obtained on normal and reversed bonded phases, in addition to bathochromic and hypsochromic effects shown by derivatives, provided effective information for identifying individual phenols. The technique was applied to the determination of phenols at ppm and ppb concentrations in water and wastewater samples.

Comparison of the sequential simplex method and linear solvent strength theory in hplc gradient elution optimization of multicomponent flavonoid mixtures

SummaryUsing a camomile flavonoid extract as the sample and four different reversed-phase partition systems, the ability of the Simplex procedure to produce optimum gradient separation of unknown multicomponent mixtures was checked against the linear solvent strength (LSS) gradient elution theory. On the same partition systems the mean solvent strenghts were measured by experimentally determined logk′ vs. mobile phase composition plots. These mean solvent strengths are compared to those inferred from the optimum gradients and the usefulness of LSS theory in multicomponent mixture gradient elution optimization is discussed.

Reversed-phase ion-pair systems to predict partition coefficients of β-carbolines by HPLC and TLC

SummaryA group of 17 β-carbolines was studied in HPLC and TLC systems in order to predict their partition coefficients (log P values). On account of the basic or acid character of some of these compounds, an ion pairing system gave the best results. Both HPLC and TLC data were comparable for log P prediction but severe pH conditions required the use of TLC plates. Retention data are quantitatively related to lipophilicity (expressed as the Hansch constant) and polarity (as the inductive constant) of the solute molecule.

Pre-concentration of organic pollutants : Potential interference from the use of styrene copolymer adsorbents

Abstract The characterization of volatile products released on heating from Porapak Q, Chromosorb 101, 102, and 103 is reported. The structures of these compounds are verified by gas chromatography—mass spectrometry. The polymers were also extracted with dichloromethane. Thermal and extraction clean-up methods are compared, with the aim of establishing the best conditions for minimizing interference in air-sampling schemes.

Influence of thermal pre-treatment on adsorption properties of porous polymer air samplers

Abstract A study of the influence of thermal pre-treatment on the adsorption properties of various polymers (Porapak Q, Chromosorb 101, 102 and Tenax GC) is reported. The linear extrapolation of ln Vg against 1/T is examined in the context of the preheating temperatures. At higher temperatures, chromosorb 101 and 102 show a polarity increase, while Porapak Q shows a decrease. For styrene copolymers, the function ln Vgversus 1/T is fully linear only when the pre-heating temperature coincides with the temperature limit suggested by the manufacturers. Pre-heating temperatures between 200 and 300°C do not influence the adsorption characteristics of Tenax GC, for which the function ln Vg, versus 1/T is always linear.

Gas-chromatographic study of the decomposition of thiocarbamic compounds as a function of temperature

Abstract A description is given of the experimental procedure developed for the simultaneous determination of hydrogen sulphide and carbon disulphide, evolved during the decomposition of metal ethylene bis-dithiocarbamates in acid media, at temperatures between 50° and 100°. The limits of sensitivity obtained with the apparatus used for the quantitative determination of these gaseous products are described. The various reaction mechanisms proposed for the decomposition of the ethylene bis-dithiocarbamates are considered, and the molar ratios of the experimentally obtained sulphur compounds in relation to the total sulphur content of the original thio-organic compoun are discussed.

Comparison of reversed-phase thin-layer and high-performance liquid chromatography of flavonoid compounds

Abstract The reversed-phase high-performance liquid (HPLC) and thin-layer chromatographic (TLC) behaviour of flavonoids with methanol, tetrahydrofuran and acetonitrile as organic modifiers was compared. Twenty-six different correlation cases, together with their statistical parameters, are presented and discussed. Both TLC and HPTLC plates were considered. The dependence of TLC incremental Rm, values from different group substitutions on solvent type, solvent composition and type of plate is considered. A method for establishing HPLC gradient elution conditions by using TLC data is discussed.