Gel Permeation Chromatography System Research Articles

Characterization of a Linear Melamine Formaldehyde Resin

A novel linear melamine formaldehyde resin on the basis of the bifunctional tetramethylmelamine was created. It was found to posses several promising properties for industrial applications. Structural characterization of the material at its various production states was achieved with different mass spectrometric techniques. Liquid chromatography-ion trap mass spectrometry was used to completely separate the resins and identify the individual components. Detection with a diode array detector indicated a change of spectroscopic properties with the degree of polymerization. The material was also analyzed with analytical pyrolysis and a gel permeation chromatography system hyphenated to a mass spectrometer in order to unambiguously determine the molar masses.

Determination of Spinosad in Vegetables and Fruits by High-Performance Liquid Chromatography with UV and Mass Spectrometric Detection After Gel Permeation Chromatography and Solid-Phase Extraction Cleanup on a 2-Layered Column

A simple and reliable method was developed for the determination of spinosyns A and D, the active ingredients of spinosad, in vegetables and fruits, by high-performance liquid chromatography with UV detection (HPLC-UV) and confirmation by mass spectrometry (MS); the method uses selected gel permeation chromatography (GPC) and a 2-layered column for solid-phase extraction system. An aliquot of the crude sample extract obtained by acetonitrile extraction is loaded into the GPC system. The fraction containing spinosyns A and D is selectively collected and loaded directly onto a 2-layered column consisting of graphitized carbon (upper layer) and cyclohexyl-bonded silica gel (lower layer). After the column is washed with the GPC mobile phase acetone-cyclohexane (3 + 7), the column is eluted with acetonitrile containing 2% triethylamine. The eluate is used for HPLC-UV/MS analysis. Average recoveries from fortified cabbage, green perilla, fig, and strawberry at analyte concentrations of 0.05 and 0.25 microg/g were >85%, and the relative standard deviations were <9%. The detection limits for spinosyns A and D in green perilla were 0.005 microg/g by UV detection and 0.001 microg/g by MS detection.

On-line coupling of high temperature GPC and 1H NMR for the analysis of polymers

The on-line coupling of gel permeation chromatography (GPC) and 1H NMR operating at temperatures up to 130 °C is presented. A NMR flow probe with a cell volume of 120 μL and a stop-flow valve are developed for on-flow and stop-flow NMR measurements at high temperatures. To maintain high and constant temperatures through the whole probe, the flow probe contains two separate heating circuits. A modified stop-flow valve is developed as a control device for enabling on-flow and stop-flow experiments at high temperature conditions. Heated transfer lines connect the flow probe with the high temperature GPC system. Due to their semicrystalline nature, polyolefins can be studied by liquid chromatography only at temperatures above 100 °C. The novel high temperature GPC–NMR system is used for the separation of complex polyolefins regarding their molar mass and for the analysis of different chemical structures. Blends of polyethylene, poly(methyl methacrylate), and ethylene-methyl methacrylate copolymers are separated according to the molar masses of the components. The compositions of the components are directly studied by on-line NMR. Moreover, the chemical composition distribution of an ethylene-methyl methacrylate copolymer sample is analysed. Differences between results of on-flow and stop-flow measurements are discussed.

Synthesis of Chromophore-Labeled Polymers and Their Molecular Weight Determination Using UV–Vis Spectroscopy

This laboratory experiment is designed to allow undergraduate students to gain experience in polymer synthesis and characterization. Polystyrene quantitatively end-labeled with fluorene is produced via atom transfer radical polymerization run under a nitrogen atmosphere, using unpurified reagents and solvents. Molecular weight characterization of the polymers is performed using UV–vis spectroscopy, eliminating the need for specialized equipment such as gel permeation chromatography. Number average molecular weight values are obtained using Beer–Lambert's law, which is used to determine the molarity of fluorene-labeled polymers in THF solutions. These calculated values consistently agreed within 11% of molecular weights obtained using calibrated gel permeation chromatography systems, demonstrating the accuracy of the results. This laboratory exercise is suitable for undergraduate students in an organic or polymer chemistry course and requires no previous experience in polymer synthesis or characterization.

Radius of Gyration of Polystyrene Combs and Centipedes in a ϑ Solvent

The molecular weight dependence of the radii of gyration R{sub g} in a {var_theta} solvent (trans-decalin) of one regular branched comb and three regular centipede polystyrenes was studied using a gel permeation chromatography system equipped with a two-angle light scattering detector and a refractive index detector. R{sub g} in trans-decalin for each sample of particular molecular weight was about 25% smaller than that in a good solvent (tetrahydrofuran, THF). On the other hand, they are 20--40% larger than the theoretical values from the Gaussian chain model. This difference can be explained with the wormlike comb model developed by Nakamura et al. (Macromolecules 2000, 33, 8323-8328). Persistence lengths thus obtained for each sample were about half of that determined in THF solution. However, they are significantly larger than that for linear polystyrene. These results suggest that a main chain stiffening effect exists in comb polystyrenes even in a {var_theta} solvent.

Perfluoropolyether characterization by nuclear magnetic resonance spectroscopy and gel permeation chromatography

Perfluoropolyethers (PFPEs) are vital lubricants in the aerospace and magnetic recording industry, and they have potential applications in micro-electromechanical and optoelectronic devices. Precise control of their physical properties requires analytical tools, such as nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC) to characterize, chain composition end groups, and molecular weight distribution. The 19 F chemical shifts for Z-, D- and K-type perfluoropolyethers, and six different end groups are compiled into tables within. Application of NMR spectra to derive the number average molecular weight and chain composition is illustrated. A GPC system was developed to measure the perfluoropolyether Zdol molecular weight distributions. Significant variation in the Zdol refractive index with molecular weight was observed in the differential refractometer during GPC. The index variation compared favorably with that calculated from the molar refraction of subunits and end groups. Oligomer peaks found in the low molecular weight tail of the molecular weight distribution are well described by a statistical model. Both the NMR spectroscopy and GPC were simultaneously employed to follow the evolution of the molecular weight distribution during Zdol evaporation.

A novel method for the determination of carbonyl groups in cellulosics by fluorescence labeling. 1. Method development.

A novel method to accurately determine the carbonyl content in cellulosic materials by fluorescence labeling with carbazole-9-carboxylic acid [2-(2-aminooxyethoxy)ethoxy]amide has been developed. The procedure can readily be incorporated into a gel permeation chromatography (GPC) system with refractive index and multiple-angle laser light scattering detection. Both a homogeneous procedure, working in DMAc/LiCl (2.5%, w/v), and a heterogeneous derivatization approach, using aqueous buffer pH 4.0, for determination of carbonyls in pulps have been optimized with regard to reaction conditions, presence of catalysts, reproducibility, and completeness of conversion. The homogeneous labeling requires prolonged reaction times and removal of excess marker prior to GPC analysis by a time-consuming precipitation-washing-redissolution sequence, which is not needed in the heterogeneous approach. The heterogeneous procedure offers the additional advantages of higher efficiency, shortened analysis times, increased simplicity, and widest applicability.

Hyaluronan molecular weight and polydispersity in some commercial intra-articular injectable preparations and in synovial fluid.

Hyaluronan is the major non-proteinaceous component of joint synovial fluid and is responsible for the unique rheological and biological properties of this medium. In joint arthropathies the molecular weight and concentration of hyaluronan may change, thereby influencing joint physiology and function. Intra-articular administrated hyaluronan derived from a number of sources, has been used for the treatment of osteoarthritis, however, there is limited information on the molecular weight and polydispersity of these various commercial preparations. The objective of this study was to develop an accurate, convenient method by which the molecular weight and polydispersity of hyaluronan may be determined and then applied to characterise the hyaluronan in synovial fluid. Characterisation of the molecular parameters of hyaluronan of different origins and in ovine synovial fluid was accomplished using a multi-angle laser-light scattering (MALLS) detector coupled to a gel permeation chromatography (GPC) system, fitted with an automatic sample injector. Seven commercially available hyaluronan preparations of reported molecular weight were analysed. The weight average molecular weight (Mw) and number average molecular weight (Mn) values obtained for 6 of the 7 preparations using the MALLS-GPC system were in good agreement with the reported values. The abnormally low values for the exception suggested that degradation of hyaluronan had occurred. The MALLS-GPC technique was then used to determine the molecular characteristics of the endogenous hyaluronan in normal ovine synovial fluids. While the Mws ranged from less than 1 x 10(6) Da to 7 x 10(6) Da the majority were between 1-3 x 10(6) Da. [mean Mw = 2.42 x 10(6), mean Mn = 2.21 x 10(6) Da]. The effects of freezing and thawing synovial fluid upon molecular weight of hyaluronan were also investigated and were found to diminish both Mz and Mw values.

Radius of Gyration of Polystyrene Combs and Centipedes in Solution

The method of Iatrou et al. (Macromolecules 1998, 31, 6697) was applied to synthesize a normal comb polystyrene sample with uniform side chains equally spaced along the main chain but with the most probable distribution in the main chain length. The molecular weights of the side chain and the connector (the part of the main chain between the neighboring side chains) were 3.5 × 104 and 2.3 × 104, respectively. The sample was analyzed using a gel-permeation chromatography system with a multiangle light scattering and refractive index detector to determine the relationship between the z-average mean square radius of gyration 〈S2〉 and the weight-average molecular weight Mw. Tetrahydrofuran (THF) was chosen as the solvent. The relation fell considerably below that for linear polystyrene. The slope of the plot of log 〈S2〉1/2 vs log Mw for the comb polymer was 0.46, a value much smaller than the Flory exponent 0.6 for linear chains in good solvents. Similar measurements were also made on polystyrene centipedes prepared by Iatrou et al., which have two side chains at each junction point. As the ratio r of the molecular weight of the side chain to that of the connector increased, the 〈S2〉 vs Mw relation was lowered. Comparison of the experimental relationship with theoretical predictions for flexible discrete chains suggested that the main chains of the two types of polymer are stiffened by the crowding of the side chains. To estimate the backbone stiffness, 〈S2〉 was calculated on the basis of the wormlike comb model whose main and side chains have different Kuhn lengths λ-1 and λs-1, respectively. With λs-1 = 2 nm and the linear mass density = 390 nm-1 (for both main chain and side chains), λ-1 was estimated so as to give the closest agreement between the calculated and measured 〈S2〉. It was found that the calculated values for the comb polymer with λ-1 = 5.5 nm agree closely with the experimental data. The data for the centipedes were also explained by the theory, which showed the backbone stiffness to increase with increasing r.

Aqueous Gel Permeation Chromatographic Methods for Technical Lignins

The molecular weights and molecular weight distributions of lignosulfonates and soda lignins were determined by aqueous gel permeation chromatography (GPC). The elution behavior of the samples, was investigated in detail to evaluate the non-size-exclusive effect in the aqueous GPC system. The ionic strength and pH are thought to be the main factors influencing the accuracy and the reliability of measurements. Solutions of 0.1M NaNO3 with pH 7 or 0.1 M NaNO3 with pH 12 were shown to be optimum for determining the molecular weight of lignosulfonate and alkali lignin. Accuracy of the method was checked by comparing the data obtained by aqueous GPC with that from vapor pressure osmometry (VPO).

99/03396 Possibility of utilization of gas-separation membranes as countermeasure for global warming

The metabolism of polychlorinated biphenyls, dibenzo-p-dioxins and dibenzofurans (PCBs, PCDDs, PCDFs) can be studied well with a cytochrome P450 containing microsomal assay. In the present study, the residues of microsomal assays were extracted with organic solvents to determine the metabolites of the studied compounds with GC-ECD and GC-MS. Extracts of microsomal assays contained a matrix which interferes with these type of measurements. The matrix was hard to remove completely with solid phase adsorption chromatography. To overcome the problem of the interfering compounds, clean-up properties of a gel permeation chromatography system were studied for this specific matrix. The clean-up was firstly studied with model compounds and two different mobile phases. Thereupon the most appropriate mobile phase was applied to the extracts of a microsomal assay. Acetone and cyclohexane-dichloromethane (CH-DCM, 1:1, v/v) were compared as mobile phases. The elution profiles of several lipids and some organohalogen compounds (OHCs) were determined. The mixture CH-DCM yielded the best separation between lipids and the OHCs. The results were discussed with a theoretical evaluation on the basis of interactions between solute, solvent and stationary phase. Recoveries were assessed for the GPC procedure and appeared to be good (98–100% for the column itselt and 80–100% for the sample transfer from vial to column). The GPC was integrated in the clean-up of the extract of a microsomal PCDF metabolism assay yielding satisfactory results.

Article

Starting from a chitosan sample with a degree of deacetylation of 71%, three separate sample sets were generated by successive deacetylation and reacetylation processes. The degree of deacetylation of samples was determined by UV spectrometry supported by thermogravimetric analysis. The molecular weight of chitosan samples was determined in a solvent system of 0.25 M CH3COOH/0.25 M CH3COONa, using viscometry and gel permeation chromatography (GPC) with a TSK-gel column. The first set of samples had a similar degree of deacetylation (DDA) but differing molecular weights. The second set of samples had a similar molecular weight but differing degrees of deacetylation. The Mark-Houwink-Sakurada constants used for the determination of viscosity average molecular weight and the universal calibration of the GPC system were K = 1.40 × 10-4 dL/g and a = 0.83. Results showed that molecular weights determined from both techniques are in good accord only at lower degrees of deacetylation. This may be attributed to the fact that the chemical structure of chitosan samples could have been largely altered with increasing or decreasing degree of deacetylation. Nevertheless, the trend with which the molecular weights vary with the deacetylation time is consistent over a limited DDA range. A literature review of molecular weight analysis of chitosan is included.Key words: chitosan, degree of deacetylation, gel permeation chromatography, molecular weight, viscometry.

Gel permeation chromatography (GPC) of repeatedly extruded polyethylene terephthalate (PET)*

The paper deals with gel permeation chromatography (GPC) monitoring of the behaviour of PET (polyethylene terephthalate) after repeated extrusions. Virgin PET was submitted to three successive extrusion/ drying cycles and then the samples were swelled with hexafluoroisopropanol and treated with chloroform. GPC analysis was carried out at room temperature on a B.C.S. Serial LC 2000 GPC system equipped with a series of four GPC columns with UV detection at 254 nm and chloroform as eluent. GPC results showed that after each extrusion step the molecular weight distribution of the PET was different and Mw, Mn and Mz decreased. These findings suggest that during each extrusion degradation occurs and that repeated extrusions, as in the case of the recycling PET, may cause an alteration of the molecular weight distribution of the original PET.

Characterization of deacetylated chitosan and chitosan molecular weight review

Starting from a chitosan sample with a degree of deacetylation of 71%, three separate sample sets were generated by successive deacetylation and reacetylation processes. The degree of deacetylation of samples was determined by UV spectrometry supported by thermogravimetric analysis. The molecular weight of chitosan samples was determined in a solvent system of 0.25 M CH3COOH/0.25 M CH3COONa, using viscometry and gel permeation chromatography (GPC) with a TSK-gel column. The first set of samples had a similar degree of deacetylation (DDA) but differing molecular weights. The second set of samples had a similar molecular weight but differing degrees of deacetylation. The Mark-Houwink-Sakurada constants used for the determination of viscosity average molecular weight and the universal calibration of the GPC system were K =1 .40 ◊1 0 -4 dL/g and a = 0.83. Results showed that molecular weights determined from both techniques are in good accord only at lower degrees of deacetylation. This may be attributed to the fact that the chemical structure of chitosan samples could have been largely altered with increasing or decreasing degree of deacetylation. Nevertheless, the trend with which the molecular weights vary with the deacetylation time is consistent over a limited DDA range. A literature review of molecular weight analysis of chitosan is included.

Integrating gel permeation chromatography clean-up in the analysis of metabolites of polychlorinated biphenyls, dibenzo- p-dioxins and dibenzofurans extracted from a microsomal assay A comparison of different mobile phases

The metabolism of polychlorinated biphenyls, dibenzo- p-dioxins and dibenzofurans (PCBs, PCDDs, PCDFs) can be studied well with a cytochrome P450 containing microsomal assay. In the present study, the residues of microsomal assays were extracted with organic solvents to determine the metabolites of the studied compounds with GC-ECD and GC-MS. Extracts of microsomal assays contained a matrix which interferes with these type of measurements. The matrix was hard to remove completely with solid phase adsorption chromatography. To overcome the problem of the interfering compounds, clean-up properties of a gel permeation chromatography system were studied for this specific matrix. The clean-up was firstly studied with model compounds and two different mobile phases. Thereupon the most appropriate mobile phase was applied to the extracts of a microsomal assay. Acetone and cyclohexane-dichloromethane (CH-DCM, 1:1, v/v) were compared as mobile phases. The elution profiles of several lipids and some organohalogen compounds (OHCs) were determined. The mixture CH-DCM yielded the best separation between lipids and the OHCs. The results were discussed with a theoretical evaluation on the basis of interactions between solute, solvent and stationary phase. Recoveries were assessed for the GPC procedure and appeared to be good (98–100% for the column itselt and 80–100% for the sample transfer from vial to column). The GPC was integrated in the clean-up of the extract of a microsomal PCDF metabolism assay yielding satisfactory results.

Liquid Chromatographic Method for the Concurrent Analysis of Sucrose Polyester, Vitamin A Palmitate, and β-Carotene in Margarine

Abstract A liquid chromatographic method is described for the concurrent analysis of sucrose polyester (SPE), vitamin A and β-carotene in margarine. The SPE and vitamins are separated from the acylglycerol by gel permeation chromatography (GPC). The GPC system is equipped with a refractive index and ultraviolet (UV) detector (313 nm) to monitor the peak elution. Following collection, the vitamins and SPE are analyzed by C-18 reverse phase chromatography. A ternary gradient of acetonitrile, methylene chloride and isopropanol with evaporative light scattering detection is used for SPE analysis. Vitamin A and s-carotene are quantitated after isocratic elution with acetonitrile/methylene chloride/methanol (700/300/2, v/v/v) as mobile phase and detection at 313 nm and 436 nm, respectively. Well resolved, interference free chromatograms were obtained for each analyte.

Kinetic investigation of the degradation of hyaluronan by hyaluronidase using gel permeation chromatography.

A gel permeation chromatography (GPC) system for the analysis of hyaluronan was set up and calibrated by means of the universal calibration method. Using GPC, a kinetic assay of the action of hyaluronidase on hyaluronan has been developed. Applying Michaelis-Menten theory and the direct linear plot we have estimated the kinetic constants of the enzyme. By evaluating the decrease of the various molecular mass averages during the enzymatic reactions, we have given a demonstration of the at random degradation of hyaluronan by hyaluronidase in the initial stage of the reaction.

Determination of planar chlorobiphenyls in animal fat

AbstractThe occurrence of the highly toxic non‐ortho substituted (planar) chlorobiphenyls (CBs) at low levels in wildlife, (human) fat, and fish generates the need for a routine analytical procedure. The use of a fully automated system for the separation of planar and non‐planar CBs, consisting of a gel permeation chromatography system, a sample preparation system employing extraction columns, and a porous graphitic carbon HPLC column is described, and tested with horse fat. Gas chromatography on capillary columns, with electron‐capture or high resolution mass spectrometric detection, is used for quantitation of the CBs.

Characterization of nonderivatized cellulose by gel permeation chromatography

AbstractThe development of a gel permeation chromatography (GPC) system for the analysis of nonderivatized cellulose in the DP range of technical cellulose products is reported. In contrast to traditional GPC, where cellulose derivatives have to be prepared, in this work the cellulose solvent cadoxen was applied for the determination of the molecular weight distribution using a special analysis system. Nuclear magnetic resonance studies of cadoxen solutions indicated no complex formation between cadoxen and cellulose. Therefore, to avoid precipitation of cellulose from the prepared solution, cadoxen was also used as eluent in the chromatographic system. For this reason a stationary phase had to be found which is stable under the given strong alkaline conditions. The utilization of Fractogel TSK as column material resulted in the separation of dissolved cellulose showing a DPv between 400 and 2000 with good reproducibility. The application of very sensitive detectors together with a GPC program allows the characterization of unknown cellulose samples of different origin within a few hours.

Gel permeation chromatography of oxyethylene/oxypropylene block copolymers

Low-molecular-weight block copolymers of ethylene oxide and propylene oxide were eluted through two gel permeation chromatography (GPC) systems; (1) tetrahydrofuran (THF) solvent with PLgel; (2) aqueous solvent with TSKgel. The elution volumes of the copolymers in the THF/PLgel system depended predominantly on chain length, whereas those in the water/TSKgel were greatly influenced by composition as well as chain length. The possibility of using GPC in two systems to estimate copolymer composition was explored.