Simona Coppi

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.

Analysis of complex mixtures by capillary gas chromatography with statistical estimation of the number of components

Abstract Evaluation of the number of components by the Davis-Giddings single chromatogram method is applied to capillary gas chromatograms of a dichloromethane extract of camomile. Various runs with OV-1 or Carbowax 20M as the stationary phase were done under different experimental conditions (column temperature programming rate and column length). The results showed that the number of components obtained by this statistical procedure does not depend greatly on the nature of the stationary phase or on the experimental conditions. The component number of the camomile extract was about 200 and the stand-alone probability at unit resolution was 0.2–0.3.

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—solid chromatographic characterization of active carbons

Abstract The characterization of two active carbons was carried out by using gas chromatographic (GC) peak parameters (mean and variance) obtained by fitting experimental data with the Edgeworth-Cramer series. These results were then compared with those obtained from mercury porosimetry, low-temperature nitrogen adsorption measurements, small-angle X-ray diffraction, scanning electron microscopy and transmission electron microscopy. With regard to mass exchange processes, the chromatographic technique yields results which agree with those obtained by the other techniques. In regard to adsorption capacity, the GC characterization is more direct and unambiguous.

Characterization of styrene-divinylbenzene column packings for liquid chromatography : Elution of some acidic compounds

Abstract The elution behaviour of nineteen substituted benzoic acids on a PRP-1 column packing was investigated. The relationships between capacity factors ( k ′) and mobile phase composition (ϕ 0 ) were studied in methanol—water systems under different ionization suppression conditions. The effect of the pH of the eluent was evaluated. It was found that the relationships between log k ′ and ϕ 0 were linear and that the selectivity can be enhanced by varying the pH of the mobile phase. Further, from a comparison of the behaviour of the solutes on PRP-1, on a laboratory-prepared Chromosorb 101 and on a C 18 column packing, it can be concluded that the solute elution may be explained by solvophobic theory.

Chromosorb 101 as a packing material for reversed-phase chromatography

A procedure for preparing a Chromosorb 101 liquid chromatographic column is described. Some column parameters such as the permeability, efficiency and peak asymmetry factor were calculated. The elution of some benzene and phenol derivatives from the polymeric column with different mobile phases was performed. The results showed that some gas chromatographic adsorbents such as Chromosorb 101 can be used as packings for high-performance liquid chromatographic columns. The behaviour of these styrene copolymers resembles that of a C18 silica bonded phase.

Separation and determination of acidic herbicides on a PRP-1 polymeric column.

Abstract The chromatographic behavior of some acidic herbicides (phenoxyacetic acids, bentazon and dicamba) was investigated on a column laboratory-packed with PRP-1, using acetonitrile—water as mobile phase. Detection was performed with a UV detector set at 220 nm. This wavelength was selected as the optimum for the simultaneous determination of the herbicides. The elution of acidic compounds is affected by the pH of the mobile phase. The greates retention and the best peak symmetry were observed at pH 2.3. The relationships between log k ′ and acetonitrile volume fraction (ϕ) in the mobile phase are parabolic. The detection limits of the tested substances were abount 0.2 ng in the volume injected. The capacity factors in pure water ( k ′ w ), extrapolated by a quadratic expression, showed that PRP -1 could be effective in extracting the examined compounds from water. Various experiments, carried out on spiked water samples using commercial PRP -1 cartridges, showed that the recovery of examined herbicides is nearly 100%. Further, such traps could make it possible to concentrate aqueous samples containing acidic herbicides at very low levels (ppt).

Correlation between chemical and physical characteristics and adsorption properties of some styrene copolymers

Abstract The gas chromatographic retention properties of Chromosorb 103 under different thermal treatment conditions are reported. The behaviour is compared with that of similar previously studied polymers, Porapak Q and Chromosorb 101 and 102. The gas chromatographic data are discussed in relation to chemical and physical results obtained by X-ray diffraction, differential thermogravimetric analysis, differential scanning calorimetry and surface area measurements.