Bimodal Gel Permeation Chromatogram of Acrylonitrile-Styrene Copolymers

Abstract

Gel permeation chromatograms were recorded for an acrylonitrile-styrene copolymer in both dimethylforamide (DMF) and DMF-LiBr-H₂O as solvents. In the DMF solvent, a bimodal chromatogram was observed, while in the DMF-LiBr-H₂O solvent, monomodal behavior was observed for the same sample. In order to investigate the cause for such behavior, the molecular weight averages of the copolymer were determined in these solvents. Further, the chromatogram in the former solvent was corrected for observed nonlinearity of the calibration curve. We concluded that apparent differences in the chromatograms are due, at best in part, to the nonlinearity. General conditions for the appearance of bimodal chromatograms were examined based on this idea, using simulation techniques.     

Characterization and Properties of Macromolecules

Abstract

The effect of solvent on the numerical results obtained from gel permeation chromatography has been evaluated. Columns packed with porous glass materials were evaluated, using three solvents. The narrow molecular weight distribution polystyrene standards were chromatographed in each solvent to calibrate the columns. The chromatograms of the standards were then analyzed to yield the molecular weight averages and their molecular weight distributions. The results indicate solvents of high viscosity should be avoided, especially for high molecular weight samples.     

Cyclic polyamide oligomers extracted from nylon 66 membrane filter disks as a source of contamination in liquid chromatography/mass spectrometry

Background interferences are perhaps an unavoidable part of analytical detection schemes, particularly when analyzing trace level samples or when using detectors with high levels of sensitivity. In liquid chromatography, mobile phase solvents are routinely filtered using membrane filter disks to trap particulates in hopes of minimizing contamination, providing improvements in data output and instrumental operation. In this study, we report that one such filter disk leads to a significant level of contamination in LC and LC/MS experiments. Extractable compounds from nylon membrane filters generate significant background signals in UV absorption chromatograms at 214 nm, and are also detected by electrospray ionization mass spectrometry, with nominal m/z values of 453 and 679. It is shown that rinsing the nylon membranes before their use can reduce, but will not eliminate, the extractable contaminants from the mobile phase. Through MS and tandem MS analysis, we have identified these contaminants as cyclic oligomers of polyamide 66. Based on these results, it is recommended that nylon membrane filters be avoided when conducting trace level analysis, particularly when conducting LC/MS experiments.     

The role of complex formation in partition paper chromatography

Further information of the possible effects of chemical reaction on differential ionic movement in partition paper chromatography was obtained by developing chromatograms of fifteen inorganic cations with alcoholic solvents containing varying concentrations of disodium ethylenediaminetetraacetate.An examination of these chromatograms indicated that variations in the concentrations of E.D.T.A. in the solvent or the presence of free acid or ammonia resulted in marked changes in R_F values and spot areas.It is therefore suggested that care should be taken in interpreting the results of any chromatograms developed with solvents capable of chemical interaction with the “spotted” solute.     

Determination of Vitamin B12 in Multivitamin Tablets by High Performance Liquid Chromatography

Abstract

Two procedures for separation and determination of vitamin B₁₂ in multivitamin tablets by reversed phase high performance liquid chromatography are proposed. Sample preparation is very simple: tablets are dissolved in distilled water, centrifuged and filtered. The sample solution is directly applied in the sample loop injector and chromatograms are obtained with gradient elution using water-methanol and water-acetonitrile as solvents. The peak of vitamin B₁₂ from samples of B-complex tablets is well separated with the two procedures. For multivitamin tablets, however, only the procedure with water and methanol as solvents was good for separation and quantification of vitamin B₁₂. Both procedures were verified by the standard addition method and also compared to a previously developed method using electrothermal atomic absorption spectrometry for vitamin B₁₂ determination.     

Hplc Method for Kinetic Study of Mutarotation of Sugars

Abstract

A high-performance liquid chromatographic (HPLC) method was established for kinetic studies of the interconversion (mutarotation) between pyranose sugar anomers in solution. At very low temperature, HPLC chromatograms of each sugar indicated the concentrations of each anomer in the state prior to the HPLC analysis. Thus, when one of the pyranose anomers obtained by recrystallization was dissolved into water and was analyzed by HPLC repeatedly, gradual changes in the chromatogrphic patterns were observed. The equilibrium concentrations of each sugar anomer in different solvents were found to vary, which was also investigated by HPLC.     

Problems in Determining Compositional Heterogeneity of Copolymers by Size-Exclusion Chromatography and UV-RI Detection System

Abstract

The compositional heterogeneity of styrene-methylmethacrylate copolymer has been evaluated by a UV-RI dual-detector method and by a RI detector-pyrolysis-gas chromatographic method and problems associated with the determination of the chemical heterogeneity by a UV-RI method are discussed. The quotient of signals H(UV)/H(RI) of both the detectors (UV and RI) for polystyrene increased at the extreme parts of the molecular weight distribution owing to nonlinearity of UV response. The correction of the quotient of signals of both detectors for the copolymer was proposed. The UV and RI response factors for the copolymer were supposed to differ from those for homopolymers. Reproducibility for the detector responses influences the values of chemical heterogeneity much more than expected. To overcome these problems, the detection method to obtain each composition independently using different detectors will be preferable.     

High-Speed Video Densitometry: Principle and Applications

Abstract

In the past few years, TV-type multichannel detectors/Vidicon-, Plumbicon-and Orthicon tubes etc./ found application in several fields of analytical chemistry/1/. Recently, video-technique was introduced to the densitometric evaluation of thin-layer chromatograms as well/2/; the term ‘video densitometry’ is used in this context.     

Size Exclusion Chromatography (SEC) of Complex Polymers - Generalized Analytical Corrections for Imperfect Resolution

Abstract

Herein is reported generalized analytical solutions which permit correction for imperfect resolution when the molecular weight calibration curve is nonlinear and the variance of single-species chromatograms changes significantly with molecular size of the polymer solute. Two kinds of generalized analytical solutions have been obtained. One is a solution of Tung's integral equation for the corrected chromatogram or the molecular weight distribution and the other is a solution for the corrected molecular weight averages of the whole polymer. Also discussed is the use of local corrections for imperfect resolution across the chromatogram with detectors such as the low angle laser light scattering spectrophotometer (LALLS) when used with micro and macropackings.     

Microgels and ionic associations in solutions of cellulose diacetate

Solutions of cellulose diacetate (CDA) from two sources (cotton linters and wood pulp Floranier) were analysed in various solvents by size exclusion chromatography (SEC). Without special precautions, the SEC chromatograms presented three peaks — or prehumps — before the main polymer peak. The first prehump which could be eliminated by ultracentrifugation corresponded to microgels whose sugar composition was determined. These microgels were also investigated by electron microscopy, X-ray and electron diffraction analysis. They corresponded mainly to cellulose triacetate (CTA-II) in the case of CDA from cotton linters and a mixture of CTA-II and xylan diacetate (XDA) in the case of CDA from the wood pulp Floranier. The second and third prehumps could be attributed to ionic effects corresponding to the association of remaining sulfate groups on the CDA molecules with residual calcium. It was found that these ionic effects could be eliminated by the addition of LiBr or LiCl to the elution solvents. This led to chromatograms devoid of prehumps.Presented in part at the Cellulose '91 meeting in New Orleans.     

Nylon 66 polymers. I. Molecular weight and compositional distribution

Results from characterization of melt-polymerized nylon 66 by various solution property measurements are reported and employed in analysis of typical molecular weight and compositional distributions for these systems. Critical attention is paid to application of standard procedures including light scattering, viscosity, membrane osmometry and other colligative property measurements in arriving at satisfactory specification of polymer molecular weight averages. Particular consideration is given to polymers extending appreciably beyond the lower and higher limits in molecular weight normally encountered. The conclusions drawn are: (1) in the range of number-average molecular weights less than about 25 000, nylon 66 as ordinarily prepared by melt condensation consists principally of linear species approximating the “most probable” distribution; (2) small amounts of cyclic oligomers are present in all samples: (3) increase in the extent of the melt polycondensation to progressively higher stages is accompanied by secondary reactions and the formation of branched components terminating ultimately in crosslinked, insoluble gels. Intrinsic viscosity–molecular weight relationships in seven solvents, applicable to nylon polymers meeting the requirements of (1) above, are derived.     

An Analysis of Imperfect Resolution in the Chromatography of Particle Suspensions

Abstract

Here-in is reported a general method of correction for imperfect resolution in the chromatography of particle suspensions. It overcomes most of the limitations of previously reported methods. A non-linear particle diameter - retention volume calibration curve and a generalised spreading function are considered. Moment equations are developed for two types of general detectors; the first type includes a refractive index detector and a turbidity detector with Rayleigh scattering while the second type includes a tubidity detector with Mie scattering. The moment equations were applied to the analysis of chromatograms of narrow Dow polystyrene latices measured by size exclusion chromatography.     

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.     

Atomic Absorption Detector for Chromium Organometallic Compounds Separated by High Speed Liquid Chromatography

Abstract

Atomic absorption spectroscopy (AAS) has been demonstrated to be a metal-specific detector for chromium organometallic compounds separated by high pressure liquid chromatography (HPLC). Column effluent from the HPLC instrument was fed directly to the aspirator of the atomic absorption instrument set to record absorption due to chromium. Well defined peaks were obtained. In addition to being specific for a given metal, the method is free of some of the constrictions placed upon conventional ultraviolet absorption and refractive index detectors commonly used with HPLC. For example, solvents which absorb strongly in the ultraviolet may be employed and there is no need to use expensive spectroquality solvents. The method promises to be particularly useful for the analysis of specific organometallic compounds found in liquefied coal and shale oil.     

Effect of Protecting Groups and Solvents in Anomeric O-Alkylation of Mannopyranose1

Abstract

Anomeric O-alkylation of mannopyranoses with various protecting groups was investigated using mannose derivatives and 2,3-O-isopropylidene-l-O-trifluoro-methanesulfonyl-D-glycerol (1) as alkylating agent. Generally, in polar solvents higher α/β ratios were obtained than in nonpolar solvents. Sterically demanding protecting groups at the 6-O-position and polar solvents led to higher yields. Reactivity differences were explained by different complex formation. Based on these results mannopyranosyl-α(1-4) glucopyranosides 26 and 27 were synthesized using mannose derivatives 5 and 6 having a 6-O-(p-methoxyphenyl)diphenylmethyl group and galactosyl trifluoromethane-sulfonate 24 or nonafluorobutanesulfonate (nonaflate) 25, respectively, as alkylating agents.     

Assessment of ethanol and acetonitrile in 18F-FDG preparations by means of liquid chromatography

Introduction Acetonitrile (ACN) and ethanol (EtOH) are common solvents used in radiopharmaceutical production. In accordance to official compendia, the concentration of these solvents should be assessed by gas chromatography. In the present paper, an optimized method, based on Koziorowski (2010), is validated. Methods ACN and EtOH concentrations and retention times (Rt) were obtained by a HPLC system equipped with a refractive index detector (RID), an ion exclusion column and ultrapure water as mobile phase. The methodology was validated following the ICH Q2(R1) requirements. Results The solvents EtOH and ACN were eluted at 23.22 and 26.32 minutes, respectively, with a final run time of 30 minutes. The validation parameters (accuracy, precision, linearity, specificity, robustness, detection and quantification limits) were obtained. Conclusions A reproducible HPLC method for the quantification of residual solvents in preparations of 2-deoxy-2-[fluorine-18]fluoro-D-glucose (¹⁸F-FDG) was described and validated. The method was precise, accurate, selective, robust and linear over a wide range. In addition, this method showed a high sensitivity, with limits of detection and quantitation comparable to the usual methods by gas chromatography.     

Data Treatment in Aqueous GPC with On-Line Viscometer and Light Scattering Detectors

Abstract

Gel Permeation Chromatography (GPC) is becoming a very powerful tool for polymer characterization with the coupling of mass detectors using viscometry and light scattering techniques. The triple coupling seems to be the best way since the light scattering detector gives absolute molecular weights and viscometric detection provides intrinsic viscosity, leading to absolute molecular weights through universal calibration and information on long-chain branching. However, instrumentation becomes more sophisticated, expensive and, simultaneously, very sensitive to several parameters which are not critical in classical GPC. Moreover, an on-line computer is required for data acquisition and appropriate software for reliable interpretation of chromatograms.

Our experiments were performed with a Waters Associates room temperature instrument in which a home-made continuous viscometer, using pressure transducers, and a light scattering detector (LALLS Chromatix-CMX 100) were inserted on-line between the column set and the refractometer. Data were interpreted through personal software written on HP9836 and PC-AT computers.

We describe, here, the behavior of some polymers in aqueous solutions, mainly those that are commonly used as calibration standards (polyethylene oxides, pullulans). Experiments were run using two different sets of columns (‘Ultrahydrogel’ from Waters Associates and ‘Shodex OH-Pak’ from Showa Denko K.K.) in several aqueous solvents, pure water or water with various salts (LiNO₃, NaNO₃, LiCl, NaCl, Na₂SO₄) at different concentrations. Intrinsic viscosities were determined through viscometric detection and weight average molecular weights through the LALLS detector, leading to a plot of universal calibration curves Log([ηl.M) versus elution volumes.     

A New Method for Identifying and Estimating the Parameters of the Instrumental Spreading Function in Size Exclusion Chromatography-Application to Particle Size Analysis

Abstract

Herein is reported a new method for identifying and estimating the instrumental spreading function in size exclusion chromatography. The method is based on the solution of the integral equation when the size distribution of the injected standards are known. A numerical method after Ishige et al. (1) to solve the integral equation for the corrected distribution is suitably modified to estimate instead the spreading function when the true and measured chromatograms are both known. The method is evaluated for synthesized chromatograms using the particle size distribution of Dow polystyrene latices. It is then applied to experimental chromatograms of the latices obtained by size exclusion chromatography. The resulting spreading functions were then analysed for variance, skewness and kurtosis.     

Formation of hydrophobic surface using a bis-urea derived organogel

A bis-urea derived gelator 1 was synthesised with a high yield via a simple organic reaction. The gelator could form organogel in four kinds of solvents. The organogels obtained from four kinds of solvents were systematically investigated by FESEM, UV–Vis, PL, IR, XRD and water contact angle experiments. It was interesting that the self-assembly process of gelator 1 could be tuned by solvents. The film structure and fibre were formed in different solvents. At the same time, the different morphologies all displayed hydrophobicity. Especially, the contact angle of the fibre obtained from organogel in DMF was up to 147°. This research would provide a good pattern for preparation of a special hydrophobic surface through supramolecular self-assembly.     

Gel permeation chromatography of polyamide by N-trifluoroacetylation

Successful chromatograms were obtained for trifluoroacetylated nylon 12 (N-TFA-N) in gel permeation chromatography (GPC) with dichloromethane as eluent. It was confirmed that the method of universal calibration was applicable for N-TFA-N and polystyrene. The average molecular weights of nylon 12 were obtained from the chromatogram of N-TFA-N by use of the calibration curve for polystyrene. The stability of N-TFA-N in solution was examined from various angles. Satisfactory results are obtained, if the sample solution is measured within 48 h after preparation.