Liquid-solid Adsorption Chromatography Research Articles

Temperature and Solvent Effect on the Molecular Size and Shape of Heavy Oil Fractions

Two kinds of heavy oil were fractionated into eight fractions by liquid–solid adsorption chromatography. The viscosity curves of relative viscosity versus concentration for dilute solutions of heavy oil fractions were determined, using the isovolume viscosity determination method. The intrinsic viscosity was obtained according to the Einstein law, and subsequently, the equivalent sphere hydrodynamic diameter was calculated. The results show that the equivalent sphere hydrodynamic diameters of heavy oil fractions are 1.1–4.0 nm under the experimental condition, while the molecular size of asphaltene is much larger than that of other fractions. The molecular size is not only related to the molecular weight but also affected by the spatial configuration of the heavy oil molecule. Different temperature and solvent conditions lead to various spatial configurations of heavy oil molecules, which results in different molecular sizes.

Molecular size characterization of heavy oil fractions in vacuum and solution by molecular dynamic simulation

Two kinds of heavy oils were fractionated into eight fractions by Liquid-Solid Adsorption Chromatography, respectively, and samples were collected to measure properties. According to the elemental analysis, molecular weight and 1H-NMR data, average molecular structures of polycyclic aromatic and heavy resin were constructed with improved Brown-Ladner (B-L) method and several corrections. And then, the most stable conformations of polycyclic aromatic and heavy resin in vacuum and toluene solution were obtained by molecular dynamic simulation, and the molecular size was gotten via the radius of gyration analysis. The results showed that the radius of gyration of polycyclic aromatic and heavy resin was 0.55–0.70 nm in vacuum and 0.60–0.90 nm in toluene solution. With molecular weight increasing, the molecular size in vacuum and toluene solution also increased. Due to the swelling behavior of solvent, the alkyl side chains of heavy oil molecule in solution were more stretched. Thus, the molecular size in toluene solution was larger than that in vacuum.

Migration from polyamide ‘microwave and roasting bags’ into roast chicken

Migration of non‐volatile and volatile compounds from ‘microwave and roasting bags’ (MRB), made of Nylon 6,6 (and some Nylon 6), into chicken meat, skin, and juices during roasting (200°C/2 h) in a conventional oven was determined. For measurement of migration of non‐volatile compounds, cooked chicken was freezedried, extracted with methanol after addition of 2‐azacyclononane (internal standard) and the extract cleaned‐up using liquid—solid adsorption chromatography (silica gel). High performance liquid chromatography (HPLC) in the reverse phase mode using a linear gradient of methanol in water was used to quantify seven Nylon 6 and Nylon 6,6 cyclic monomers and oligomers of molecular mass up to 678 daltons. Migration into chicken was 7.48 μg/g (8.26 mg/bag; 3.94 μg/cm2), 16% of the total non‐volatile compounds contained in the MRB material. Individual migrants were also quantified. Migration of one volatile compound, 2‐cyclopentyl cyclopentanone, into the roast chicken parts was measured. Extraction with diethyl ether, using a modified Likens‐Nickerson system of concurrent steam distillation—solvent extraction with an internal standard (cyclohexanone) was performed for 10 h. Gas chromatography/mass spectrometry (GC/ MS) in the selected ion mode (SIM) was used for quantification. An average of 14.0 (±4.36) μg/bag (or μg/chicken) migrated, being 0.08% of the total 2‐cyclopentyl cyclopentanone present in MRB. Loss of volatile compounds to the atmosphere is believed to have occurred since there was another, more volatile compound (cyclopentanone), present in MRB, at levels higher than 2‐cyclopentyl cyclopentanone, but this was not detected in roast chicken. In general, the transference of MRB components into roast chicken can be considered not to present a hazard.

Microdialysis- liquid chromatographic study on competitive binding of drugs to protein

A new method to determine the interaction between drug and protein has been developed by utilizing the technique of microdialysis sampling with the ketoprofen and the human serum albumin (HSA) as the model of drug and protein. Two kinds of binding sites of HSA to ketoprofen have been observed. The binding constants and number of binding sites obtained by the Scatchard equation are 0.799, 3.18×lo6 mol-1 ·L and 2.15, 2.01×105 mol-1 ·L, respectively. The displacement binding of drugs to HSA has also been studied. The strong displacement of competitive binding of ibuprofen with ketoprofen to HSA was observed, which means that the primary binding site of HSA to ketoprofen and that to ibuprofen are the same. However, only a weaker displacement of warfarin for the association of ketoprofen with HSA was observed, which may suggest that the primary binding site of HSA to ketoprofen is different from that to warfarin. Such a displacement effect for competitive binding of drugs to HSA was explained by the displacement model in the liquid-solid adsorption chromatography.

Adsorption liquid chromatography on silica for the chiral separation of amino acids and asymmetric amines derivatized with optically active N-α-9-fluorenylmethyloxycarbonyl-amino acid-N-carboxyanhydrides

Optically pure N-α-Fmoc-amino acid-N-carboxyanhydrides (Fmoc-AA-NCAs, Fmoc=9-fluorenylmethyloxycarbonyl) are proposed as precolumn reagents for the chiral analysis of asymmetric amines including α-amino acid alkyl esters. Separation of diastereomers arising from racemic amines is better achieved by liquid-solid adsorption chromatography on silica than by reversed-phase techniques. The sample preparation is easily performed while the properties of the Fmoc group allows high sensitivity by fluorescent detection. In this mode, picomolar limits of enantiomeric excess are detected.

Theory of liquid-solid adsorption chromatography with mixed eluents on energetically heterogeneous adsorbents

Theory of liquid-solid adsorption chromatography with mixed eluents on energetically heterogeneous adsorbents

SULFUR COMPOUNDS IN HIGH-BOILING FRACTIONS OF SAUDI ARABIAN CRUDE OIL.

Abstract This study describes the isolation and characterization of sulfur compound types in high boiling distillate of Arab crude oil. Thu distillates were prepared by physical and chemical methods like adsorption chromatography and complexation with mercurous nitrate and iodine. Spectrophotometry methods were used for detection and identification. The sulfur compound types, thus obtained, were classified into aliphatic sulfides, aromatic sulfides, and thiophencs. Sulfides represented the most abundant type of sulfur compounds in the distillate. The 225-500°C boiling range distillate was fractionated into four distillate cuts using molecular distillation and each cut was further separated into three chromatographic fractions, saturated hydrocarbons, aromatic hydrocarbons, and sulfur concentrates by using liquid solid adsorption chromatography on a dual packed (silica-alumina) column. The chromatographic separation was effectively monitored by measurement of refractive index, ultraviolet spectroscopy, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The complex aromatic sulfur concentrates were analyzed by gas chromatography using flame photometric and flame ionization detector, infrared spectroscopy, and gas chromatography - mass spectrometry. Benzothiophcnes, dibenzothiophencs, naphthobenzothiophenes and homologs are found to be the major sulfur compound types in the distillate fractions.

A new equation for the retention of solutes in liquid–solid adsorption chromatography with mixed mobile phases

A new equation for the dependence of the capacity ratio k′ of solutes on the composition of a binary mobile phase in liquid–solid adsorption chromatography has been derived. Starting from the general definition of the chromatographic retention in terms of surface excess quantities, and then introducing a monolayer model for adsorption from three-component mixtures, a three-parameter relation for k′ in terms of the compositions of the surface layer and the mobile phase is obtained.

Polymer adsorption chromatography with evaporative light-scattering detection

Poly(alkyl acrylate) and poly(alkyl methacrylate) homopolymers and copolymers are eluted from silica with toluene-2-butanone solvent gradients. The polymers are separated by liquid-solid adsorption chromatography according to their chemical composition and not by molecular weight. Evaporative light-scattering monitors polymers that may be difficult to detect by spectrophotometry and also permits the use of good polymer solvents that are themselves strongly absorbing. This extends the application of column liquid chromatography to a broad range of synthetic polymers that previously were amenable only to thin-layer methods.

Adsorption from multi-component liquid mixtures on to heterogeneous solid surfaces: the role of adsorption of water on silica in liquid—solid adsorption chromatography

The water content in mixed solvents that are used as mobile phases in liquid—solid adsorption chromatography on silica surfaces has been reported to play a special role in controlling the retention of solutes. The phenomena reported in the literature were investigated by a theoretical treatment: a priori calculations of the activity coefficients allow the influence of non-ideal mixing in the mobile phase to be estimated. Following a concept of “competitive adsorption within a multi-layer model”, the water coverage at the surface was calculated as a function of its bulk phase concentration, and the concentration range of water in the bulk phase was calculated where multi-layer adsorption of water on the surface takes place. Subtracting the influence of solute activity coefficients from measured capacity factor data, the competitive behavior of the three solvent components with respect to the solute was studied and the competitive adsorption constants were approximately evaluated by regression. Finally, the possible influence of the water content on the surface phase activity coefficients is discussed, assuming a geometric arrangement of oriented adsorbates.

Theoretical Foundations of Liquid Adsorption Chromatography with Mixed Eluent

Abstract One of the main advantages of liquid-solid (adsorption) chromatography (LSC) with mixed eluent is the possibility of modification of the capacity ratio over a wide range by changing the eluent composition [1]. It means that the resolution and the analysis time may be optimized by correct choice of the eluent composition (isocratic LSC) or by eluent programing during the chromatographic process (gradient LSC). Optimization of the chromatographic process requires of the knowledge of dependence of the chromatographic quantities on the eluent composition [2–5]. Increasing interest in gradient LSC [2–13] has created a pressing need for the elucidation of the theoretical basis of LSC with mixed eluent.

High-performance liquid—solid adsorption chromatography of spiropyran-end-labelled polystyrenes

High-performance liquid—solid adsorption chromatography is used to separate uncoupled and coupled spiropyran-end-labelled polystyrenes from unlabelled polymer chains. Selective separations according to molecular weight, end-group differences, or both are obtained by using adsorbents of 6- and 50-nm pore diameters with mobile phases differing in elution selectivity.

An empirical relationship between the eluant strength parameter ε° and solvent lewis acidity and basicity

It has been found that Snyder's eluant strength parameter ε°, used in liquid-solid adsorption chromatography, can be well described by a complementary Lewis acid-base model for solute-solvent interactions: ε°=0.152+0.859 · E N T + 0.332 · B KT( cf Eq.9), with a correlation coefficient of r = 0.949 for 28 solvents. This result is in agreement with the theoretical interpretation of ε° The correct statistical procedure for estimating the significance of added explanatory parameters in the sequential multiparameter regression analysis is shown ( cf Appendix). A comprehensive list of improved Kamlet-Taft solvent basicity parameters, B KT, is given.

The determination of chlorinated long-chain paraffins in water, sediment and biological samples

Methods are described for the routine determination of traces of industrial chloro-n-paraffins having 13–30 carbon atoms and chlorine contents of 42–45% (frw/w), in environmental samples of water, sediments and biota. The procedures are based on thin-layer chromatography detection and measurement. All samples are cleaned up by liquid—solid adsorption chromatography and thin-layer chromatography but those rich in lipids require preliminary solvent extraction. The methods distinguish between chloro-n-paraffins based on long carbon chains (C 20–C 30) and those based on shorter chains (C 13–C 17). The methods cover the ranges 500 ng l −1 to 8 μg l −1 for water (i.e. from about the solubility limit upwards) and 50 μg kg −1 to 16 mg kg −1 for sediments and biota. The precision of the methods ranges from ± 50% relative at the lowest concentrations to ± 12% relative at the highest. Recoveries are about 90% for water, 80% for sediments and between 80 and 90% for biota according to sample type.

Dependence of the capacity ratio on the composition of the binary mobile phase in liquid—solid adsorption chromatography

The dependence of the capacity ratio on the composition of the binary mobile phase is discussed in terms of Snyder's treatment. The relationships obtained for the capacity ratio have been tested on experimental data. The derivation of the relationship for the capacity ratio discussed by Jandera and Churacek has been examined.

Column elution and concentration of volatile compounds in biological fluids

A new solvent elution method is described for the isolation and concentration of volatile metabolites in biological fluids. The procedure involves elution of the sample with a solvent through a micro-column of an adsorbent into glass-wool and evaporation of the excess solvent in a stream of helium at room temperature. The volatiles are recovered by subsequent heat desorption into a chromatographic system. Both elution and evaporation are made in a single step using a novel sampling device. Since the technique is based on liquid-solid adsorption chromatography, the adsorbent-solvent system which gives the maximum yield of volatile constituents was studied. The method is simple, highly efficient and reproducible, requiring only small volumes of biological fluids (less than 100 μl).

Separation of catecholamines and their metabolites by adsorption, ion-pair and soap chromatography

The separation of catecholamines and their metabolites has been carried out by high-performance liquid chromatography using three systems: liquid-solid adsorption, ion-pair partition, and soap chromatography. In the last newly developed technique a reversed-phase packing is used in conjunction with an aqueous organic eluent containing a detergent. The detergent is chosen so that its ion can form ion-pairs with ions of the solutes. Soap chromatography proved the best technique in terms of column efficiency (giving 3000–5000 plates in 125 mm), resolution and sensitivity of detection. Noradrenaline, adrenaline and dopamine, their 3-O-methyl derivatives, l-3,4-dihydroxyphenylalanine, homovanillic acid and other related compounds could be separated in less than 10 min at the 10–50-ng level on columns whose plate heights were in the range of 20–40 μm. The dependence of retention on the concentration of organic modifier and on detergent concentration for three anionic detergents is reported. The method is applied to the direct analysis of urine and the potential of the method for such analyses, especially of pathological urines is demonstrated. Soap chromatography is likely to enlarge the scope of application of high-performance liquid chromatography to biochemical analysis. It is a powerful method for the separation of ionizable compounds which could replace conventional ion-exchange chromatography.

Separation of tricyclic psychosedative drugs by high-speed ion-pair partition and liquid-solid adsorption chromatography

The application of high-speed ion-pair partition and liquid-solid adsorption chromatography to the separation of twenty common tricyclic tranquilizers and anti-depressant drugs is described. In the ion-pair system, amine-perchlorate ion-pairs were extracted from an aqueous stationary phase supported on 10-μm silica gel by organic eluents containing a chloromethane and a higher aliphatic alcohol, and chromatographic parameters for elution by eight eluent mixtures are presented. Using 5 mm × 120 mm columns good separations, according to chemical class, were achieved. For adsorption chromatography, the components were eluted from 20-μm spherical alumina using eluents containing methylene chloride, n-hexane or n-pentane, and acetic acid. Chromatographic parameters are given for eight eluent compositions. Components differing little in structure are well separated by liquid-solid adsorption chromatography. Compared with ion-pair partition chromatography, adsorption chromatography is much more selective for compounds of the same chemical type. The two methods are therefore complementary. Both methods gave plate heights in the range of 0.1 to 0.3 mm.

Optimized Solvent Programming for Separations of Complex Samples by Liquid-Solid Adsorption Chromatography in Columns

In most chromatographic procedures, the efficient separation of a complex mixture requires a systematic change in sample distribution coefficients (K values) during separation. In the case of liquid-solid column chromatography, this is best accomplished by some form of solvent programming (stepwise or gradient elution). The present paper provides a theoretical derivation of sample resolution in solvent programmed systems as a function of the solvent program and other experimental variables. Conditions for optimum sample resolution per unit time are discussed. The application of these results to specific problems is straightforward and simple. Various other aspects of optimized solvent programming are also discussed. Some experimental examples of high resolution separation by solvent-programmed liquid- solid chromatography are shown.

Column efficiency in liquid-solid adsorption chromatography. H.E.T.P. [height equivalent to a theoretical plate] values as a function of separation conditions

Column efficiency in liquid-solid adsorption chromatography. H.E.T.P. [height equivalent to a theoretical plate] values as a function of separation conditions