The Use of Toluene as a Carrier Solvent for Gel Permeation Chromatography Analyses of Asphalt

Abstract

Toluene, used as a carrier solvent in GPC analyses provides different elution profiles for asphalt materials than does THF. With proper precautions and technique, chromatogram reproducibility is excellent. GPC analyses of Corbett fractions in both THF and toluene provide insight into the refractive index, solvent power, and column interaction effects which give rise to the different elution profiles in toluene. The differences provide additional information on asphalt composition which may be of use in predicting asphalt performance.     

Characterization of Nylons by Gel Permeation Chromatography and Low Angle Laser Light Scattering in 2,2,2-Trifluoroethanol

Abstract

A GPC method was developed for the analysis of several commercial nylons in trifluoroethanol + 0.05M LiBr using a styrene-divinylbenzene column custom-packed by Jordi Associates.

A broad molecular weight standard method was developed by interfacing GPC with LALLS to give the absolute molecular weight for each data point or elution volume along the chromatographic peak from a nylon sample of known molecular weight. The integrity of the interface was verified by static LALLS measurements; no loss or adsorption of solute was found in the chromatographic system.

A strong ionic effect was observed for nylon samples and the method to alleviate it was described. The molecular weights and distribution of the following nylons were determined by this method: nylon 6, nylon 4,6, and nylon 6,6. Much higher than quoted molecular weights were obtained for nylons when polymethyl methacrylates and ethylene glycols were used as standards; this necessitated the use of this broad molecular weight method for column calibration. The ambient operating conditions offered several advantages over the conventional m-cresol solvent which required operation at higher than 100 C in order to reduce the viscosity, possessed a strong odor, and occasionally resulted in degradation of polyamides.     

A Queous Exclusion Chromatography

Abstract

The exclusion chromatography of water-soluble polymers has been a field of intense activity in recent years. Although polysaccharide gels like Agarose and Sephadex have long been used for the size separation of proteins (“gel filtration”), only the advent of new hydrophilic column packings could lead to the widespread application of aqueous GPC to syllthetic polymers. These new substrates are produced with the mechanical strength and the uniformity and control of both particle- and pore-size distributions requisite to the packing of high-efficiency columns. Such columns offer good separation of species of different molecular weight (MW) along with minimal band-spreading, and so car? provide, in principle, detailed and accurate MW distribution data coupled with short analysis times. MWD accuracy and assay speed - relatively unimportant in most bio-chemical research laboratories - are paramount considerations in the industrial laboratory involved with synthetic water-soluble polymers.     

Supplement to the Method of Weiss-cohn-ginsberg in Gel-Permeation Chromatography

Abstract

Methods are proposed to transform GPG chromatograms into molecular mass distributions /MMD/ using the universal calibration and the intrinsic viscosity of the material measured at GPC circumstances, and in conditions, for which KMHS-constants are known. The results of the calculation are the MMD and the interrelation between the Kuhn-Mark-Houwink-Sakurada constans, K and a for GPC circumstances. It is also shown, that as a simplification a-values available for any condition can be used for the calculation using the experimentally measured intrinsic viscosities in GPC circumstances and within circumstances, for wich KMHS-constants are known.     

Remarks on the Calibration of Steric Exclusion Liquid Chromatography by Polymolecular Standards

Abstract

The relation of polymer molecular characteristics versus chromatographic parameters in steric exlusion liquid chromatography (GPC) was considered as a typical black box problem. Practical problems were discussed for cases of the GPC black box calibration with polymolecular polystyrene standards and of using an improper calibration model. It was concluded that checking the reliability of the GPC black box calibration is of utmost importance especially when narrow calibration standards are not available.     

Characterization of Copolymers and Polymer Mixtures by Gel Permeation Chromatography

Abstract

Estimation of molecular weights from GPC data is complicated when the polymer sample consists of a mixture of homopolymers or of statistical copolymers with nonuniform compositions. This is because sizes of solvated polymer coils depend on solvent interaction with both the homo-and hetero-units of the copolymers and because the extent of solvation of different homopolymers can differ. The overall degree of solvation may change effectively with composition and use of a single “average” set of Mark-Houwink constants in calibration procedures will then produce false molecular weight data from the GPC data. A new molecular weight average, M _x, is defined to overcome this problem. This average can be determined from the GPC chromatogram and intrinsic viscosity of the sample in the GPC solvent. Mark-Houwink coefficients are not needed. M _x lies between M _w and M _z.     

Use of Gel Permeation Chromatography in the Crime Laboratory

Abstract

In this study, the ways in which GPC can be integrated into the crime laboratory's present analytical scheme for polymer products will be examined. Fingerprint chromatograms and chromatograms illustrating molecular weight determination of two types of commonly encountered physical evidence (fibers and tail light lense fragments) will be compared and discussed. The techniques involved in sample preparation and data interpretation will be given. Finally the potential advantages of GPC for use in the crime laboratory will be presented.     

Size Exclusion Chromatography of Polyamides

Abstract

We report here a new chromatographic method for characterization of polyamides and polyether-block-amide copolymers by Size Exclusion Chromatography. First, it concerns absolute characterization of polyamide probes by classical light scattering and Ubbelohde viscometry measurements and the choice of narrow distribution standards to calibrate the GPC system. The GPC analysis of polyamides 6, 11, 12 and copolymers is based upon the dual detection refractometer/on-line continuous viscometer at 130°C using columns packed with cross-linked polystyrene gels, benzyl alcohol as mobile phase and polytetrahydrofuran standards for calibration. The main results are absolute average molecular weights and distribution curve, intrinsic viscosity and viscosity law. In addition, viscometric data produced evidence of long-chain branching occuring beyond a limiting molecular weight in some polyamide 12 samples.     

Gel Permeation for the On Line Removal of Proteins from Plasma Samples Prior to HPLC

Abstract

Gel permeation chromatography (GPC) has been investigated for the on line removal of proteins from plasma samples prior to their analysis by HPLC. The results show that GPC is a mild and effective way to remove proteins from plasma samples. It can very well be coupled on line to HPLC, providing the solutes are suitable for preconcentration on the analytical column itself or on a small pre-column, after the GPC. Under these conditions excellent reproducibility and accuracy can be obtained.     

Gel Permeation Chromatography of Polyethylene Terephalate

Abstract

This paper describes the development of the gel permeation chromatography (GPC) technique for the measurements of cyclic trimer content, molecular weights, and molecular weight distribution of polyethylene terephthalate (PET), utilizing a solvent system of o-chlorophenol-chloroform. Mark-Houwink constants for this solvent system are also described.

The GPC technique was applied to the study of the cyclic trimer content, molecular weights and molecular weight distribution of a variety of commercial PET resins. The results indicate that the cyclic trimer content in PET is dependent on molecular weight, polycondensation process and catalyst system. Solidstate polymerized PET contains less cyclic trimer than PET made by the melt-phase process of the same molecular weight. The cyclic trimer content in solid-stated PET appears to be dependent on the conditions of solid-state polymerization.

The polydispersity index determine for a variety of PET samples is higher than the theoretically predicted value of 2.0; however, there is no systematic dependence on molecular weight or polycondensation process.     

Atypic Gel Permeation Chromatography of Alcohols

Abstract

The elution behaviour of alcohols in the systems Bio Beads SX-8/dichloromethane and Sephadex LH-20/dichloromethane is investigated. On Bio Beads SX-8 the elution volumes are lower than expected for normal GPC behaviour, which is perhaps due to hydrogen bonding in solution. On Sephadex LH-20 adsorption takes place by means of hydrogen bonding, which can be used for very selective separations.     

Overloading and Degradation Study in GPC Using Low Angle Laser Light Scattering Detector (LALLS)

Abstract

The unique macromolecular compression effect or delayed GPC elution of high M.W. material was observed using the GPC + LALLS technique for a polystyrene standard of M.W. 5.0 E5. Further overloading which resulted in nonlinear fractionation is also described. The degradation of a 4.2 E6 standard after elution was detected by LALLS with calculated M.W. of 1.0-1.1 E6 but not by GPC, as indicated by normal GPC retention time and the shape of the chromatogram. This degradation was further verified by reinjection of the collected fractions into the GPC which showed a bimodal distribution with calculated M.W. of ca. 1.0 E6 via GPC calibration and LALLS. The source of degradation was attributed to the 2 micron exit frit in the single Jordi mixed bed column. Similar degradation of 2.3 E6 standard to same M.W. of ca. 1.0 E6 was also observed. The use of these standards as GPC calibrants should not be affected by this “post column” degradation.     

The Effect of Temperature on GPC for the Separation of PCBs from Transformer Oil and Subsequent Analysis by GC-MSD

Abstract

The analysis of PCBs often involves lengthy and expensive cleanup procedures to remove interferences associated with environmental sample matrices. Gel permeation chromatography (GPC) has proven to be a useful tool in removing many of these interferences from environmental samples, especially from difficult matrices such as oils, lipids and sediments. This paper describes the effect of temperature upon the GPC column in separating PCBs from transformer oil and its implication on GC-MS analysis.     

The Errors in the Treatment of Gel Permeation Chromatography Data: Origins and Corrections

Abstract

This paper deals with the origins of errors in data interpretation when using modern GPC with dual detection (refractometer-viscometer) as a method of determination of average molecular weights of polymers. We describe here the different errors classified in two groups: typical chromatographic errors and data treatment errors and we show that they can lead to very miscalculated molecular weight values. For every case, we have tried to propose the best way to avoid or correct these errors so as to use modern GPC as a very accurate method of polymer characterization.     

Gel Permeation Chromatography of Polyelectrolytes

Abstract

The mechanisms are discussed which control the GPC elution of ionic solutes, both the polyelectrolytes and the low molecular salts. The processes involved are quite general and valid in organic and in aqueous solvents. The conclusion is that gel permeation chromatography is a powerfull method to characterize poly-electrolytes; and it is shown that the correct data on molecular weight distribution can be obtained when the ionic content in the eluent is larger than 5.10^?2 M and when the concentration injected is lower than the critical overlapping concentration. The interpretation of chromatograms can be performed using the universal calibration and a viscosimetric detector.     

High-Performance Gel Permeation Chromatography of Pectins

Abstract

A high-performance gel permeation chromatographic (GPC) method was developed to determine the molecular weight distribution of pectins. The chromatographic system consisted of a hydrophilic coated silica (SynChropak) as the packing and a pH 3.7 acetate buffer as the mobile phase. By use of this system, high-methoxy, low-methoxy, and amidated pectins could be analyzed within fifteen minutes. By determining partition coefficients (K_d) of pectins as a function of mobile phase composition, K_d values were found to be independent of ionic strength from 0.055 to 0.7 M using pH 3.7 acetate buffers, which was in agreement, with intrinsic viscosity data.     

Study On The Concentration Effect In Gel Permeation Chromatography. I. A New Model Theory For Concentration Dependence Of Hydrodynamic Volumes And Gpc Elution Volumes

Abstract

A new model theory for concentration dependence of hydrodynamic volumes and GPC elution volumes was proposed. In this theoretical model both the reduction of hydrodynamic volumes and the viscosity phenomena in the interstitial volume are taken into account at the same time. The effective hydrodynamic volumes, Vhs, of a solvated macromolecule decrease with increasing reduced viscosity, (7_sp/c), and the GPC elution volumes,Ves, increase with increasing concentration, c, and intrinsic viscosity,(7), respectively according to the following relations.     

Determination of the Molecular Weight Distribution of Polyethylene Terephthalate by Gel Permeation Chromatography

Abstract

The determination of the molecular weight distribution of polyethylene terephthalate by GPC at room temperature is described. The solvent used is o-chlorophenol-chloroform (1:9) and pure chloroform is used as eluent. K and alpha of the Mark-Houwink equation of polyethylene terephthalate and of polystyrene in this solvent system were obtained. It was shown that the universal calibration can be applied.     

Solvation and Adsorption Effects in Gel Permeation Chromatography

Abstract

Saturated hydrocarbons are generally eluted according to molecular volumes in gel permeation chromatography (GPC). Other compounds, containing polar groups such as hydroxyl and carbonyl groups, deviate from the molecular volume/elution count relationship which is prepared using saturated hydrocarbons. The deviation is more or less observed regardless of the kinds of eluents. In this paper, this problem is investigated in detail with respect to infrared(IR) and proton magnetic resonance(NMR) spectra, and concentration dependences of peak heights and elution volumes in GPC. IR and NMR spectra reveal that alcohols, ketones and esters are strongly solvated by eluent molecules such as chloroform and tetrahydrofuran(THF). The solvation effect leads to faster elution for these compounds than expected for aliphatic hydrocarbons. On the other hand, the concentration dependences of elution counts and peak heights prove the adsorption of amines on polystyrene gel in chloroform. In fact, the elution rates of amines and polychlorides are retarded. In the case of aliphatic carboxylic acids, the elution mechanism is more complicated: association and adsorption effects would be overlapped.     

Separation of Methylated Purines by High Pressure Liquid Chromatography

Abstract

This paper reports a method for the separation and measurement of methylated purines of interest to carcinogenesis studies by high-pressure liquid chromatography (HPLC) following their column chromatographic isolation from collected urine samples. HPLC was evaluated on three different cation-exchange columns, with optimum conditions obtained on a Partisil 10-SCX column employing isocratic elution with 0.25M (NH₄)H₂PO₄ at pH 4.0. This column was also found to be useful for the separation of mono-methylguanine isomers. Application is shown to the analysis of rat urine following animal treatment with methyl methanesulfonate.