A. Betti

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.

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.

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.

The effect of electrolytes in the stationary phase on gas—liquid chromatographic elution

Abstract To determine the effects exerted on the gas chromatographic elution of many aliphatic and aromatic compounds by the electrolytes LiCl, CsCl, KCl and KOH dissolved in the stationary phase (Carbowax 400), the authors compared the retention volumes obtained in the presence and absence of electrolytes in the stationary phase, and calculated the change in the partial molar free energy Δ G O t ,1→2 accompanying the transfer of one mole of a solute from one stationary phase to the other. While the electrolytes in their behaviour. Aliphatic hydrocarbons showed a stronger salting-out effect than aromatic ones. While primary alcohols exhibited a considerable salting-in effect, tertiary ones showed a salting-out effect, the behaviour of secondary ones being intermediate. The experimental results may find applications in analysis.

Gas chromatographic behaviour of C1C5 alcohols on carbowax 400

Abstract The gas chromatographic behaviour of C 1 C 5 alcohols and chloroform on Carbowax 400 was studied in the range 58–88°. The specific retention volumes were determined, and the deviations from the expected order of elution were investigated by calculating the activity coefficients and the thermodynamic excess functions. The F lory -H uggins theory was used to evaluate the statistical contribution made by the mixing of molecules of different sizes, and the results were interpreted on the basis of the theory of associated ideal solutions. The difference between the order of elution of alcohols and the order of their boiling points was found to be due to differences in their molecular volumes. On the other hand, the nature of the association between the alcohols and Carbowax 400 is not very different from that of the associated species in the pure alcohol samples. The relative volatilities may therefore be predicted from the F lory -H uggins theory.