Determination Of Molecular Mass Distribution Research Articles

Matrix Assisted Laser Desorption (MALDI), a versatile tool for the characterization of Dendrimers

Matrix Assisted Laser Desorption (MALDI) is a soft ionization technique used in modern day chemistry to analyze polymers with high precision and speed. This technique does not require any polymer standard for mass calibration (as in the case of gel – permeation chromatography GPC). Protocols require only minimum amounts of solvent and consumables. Measurements of the masses of individual oligomers facilitate the determination of masses of monomers and end groups. This overview discusses the application and use of MALDI for the determination of molecular mass distribution of oligomers and end groups. However, biomolecules and other polymers with a polydispersity index (PDI) greater than 1.2 are not suitable candidates for this analysis owing to signal intensity discrimination against higher mass oligomers.

Characterization of Low-Molecular Weight Iodine-Terminated Polyethylenes by Gas Chromatography/Mass Spectrometry and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry with the Use of Derivatization

Gas chromatography/mass spectrometry (GC/MS) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry, in conjunction with various derivatization approaches, have been applied to structure determination of individual oligomers and molecular-mass distributions (MMD) in low-molecular mass polyethylene having an iodine terminus. Direct GC/MS analysis has shown that the samples under investigation composed of polyethyelene-iodides (major components) and n-alkanes. Exchange reaction with methanol in the presence of NaOH gave rise to methoxy-derivatives and n-alkenes. Electron ionization mass spectra have shown that the former contained terminal methoxy groups indicating the terminal position of the iodine atom in the initial oligomers. MMD parameters have been determined with the aid of MALDI mass spectrometry followed by preliminary derivatization-formation of covalently bonded charge through the reaction of iodides with triphenylphosphine, trialkylamines, pyridine or quinoline. The mass spectra revealed well-resolved peaks for cationic parts of derivatized oligomers allowing the determination of MMD. The latter values have been compared with those calculated from GC/MS data.

Thermogravimetry for measuring the molecular mass distribution of perfluorinated oligomers

A method for determinoffing the molecular mass distribution (MMD) in mixtures of perfluorinated oligomers based on analysis of the differential thermogravimetric (DTG) curves (temperature dependences of the rate of mass loss) is proposed. It is indicated that this method allows us to measure the MMD of oligomers whose boiling temperature is less than the temperature of their thermal decomposition, and the total portion of longer oligomers. This method was applied to the determination of MMD of products of the radiation-chemical telomerization of tetrafluoroethylene in solution.

Determination of molecular mass distribution of amylopectin using asymmetrical flow field-flow fractionation

The molar mass ( M w), radius of gyration ( R g), diffusion co-efficient ( D), and hydrodynamic radius ( R h) of amylopectin (waxy maize starch) has been determined using asymmetrical flow field-flow fractionation coupled with multi-angle light scattering and refractive index detectors (AF4/MALS/RI). A high pressure microwave vessel (HPMV) was used to dissolve amylopectin in 1 M KSCN. The effect of varying the flow rates on the M w and R g distributions of amylopectin were investigated to determine the optimum flow rates. The average M w and R g values of amylopectin determined using the Berry and Debye equations. D and R h values were determined directly from the AF4 retention times and compared to values obtained by dynamic light scattering.

Distribution analysis of ultra-high molecular mass poly(ethylene oxide) containing silica particles by size-exclusion chromatography with dual light-scattering and refractometric detection

Two different size-exclusion chromatography (SEC) systems, connected in-line either to a low-angle light scattering (LALS) or to a multi-angle light scattering (MALS) detector, are employed for determination of molecular mass distributions (MMD) of poly(ethylene oxide) (PEO) samples having a weight average molecular mass up to eight millions. The detrimental effect of the presence of strongly scattering silica particles in the samples on the light scattering signal can be eliminated using a suitable sample dissolution procedure utilizing silica solubility in aqueous mobile phase. The selection of flow-rate and sample concentration have a large impact on the obtained results. Hydrodynamic retardation phenomena and nonlinearity effects are shown to introduce severe errors in the molecular mass distributions unless flow-rate and sample concentration are kept at sufficiently low levels. Self-compensating ability of the dual detection in flow-rate effects is shown to be the main advantage here. A good agreement between the results obtained using LALS and MALS detection is found provided that a carefully selected angular extrapolation procedure is used in the case of MALS data. Thus, using carefully selected experimental conditions, SEC with light-scattering (LS) and refractometric detection proved to be an efficient technique for MMD characterisation also of ultra-high molecular mass (UHM) PEO polymers.

Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

AbstractSolution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h−1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.

Development of asymmetrical flow field-flow fractionation–multi angle laser light scattering analysis for molecular mass characterization of cationic potato amylopectin

The goal of this study is to investigate the applicability of asymmetrical flow field-flow fractionation (AsFlFFF)–multi angle laser light scattering (MALLS), and to develop a method for analysis of cationic potato amylopectin (CPAP) having ultrahigh molecular mass (UHM r). Use of the aqueous carrier having low salt content (3 m M NaN 3) resulted in a distortion in AsFlFFF fractograms of CPAP with a general pattern of a sharp rise at the beginning of the elution followed by a long tailing, probably due to combination of attractive and repulsive charge interactions (attractive interaction between CPAP molecules and the channel membrane, and repulsion among cationic CPAP molecules). As the cross flow-rate ( F c) increases, the tailing tends to increase, and the repeatability of the AsFlFFF retention data tends to decrease, which is an indication of the presence of the charge interactions. The tailing gradually decreased, and the repeatability of the AsFlFFF retention data increased, as the salt content of the carrier increased. The distortion of the fractogram finally disappeared at F c of about 0.2 ml/min and the channel flow-rate ( F out) of about 1 ml/min with the aqueous carrier having the salt content of 40 m M (3 m M NaN 3+37 m M NaNO 3). The weight-average molecular mass ( M w) and the z-average radius of gyration (〈 r g〉 z ) determined by MALLS were 5.2×10 7 and 34×10 1 nm, respectively. With the flow-rate ratio, F c/ F out kept constant, the degree of the charge interactions (and thus the distortion of fractogram) seems to increase with the cross flow-rate ( F c) and with the sample injection mass. AsFlFFF–MALLS was applied for determination of molecular mass distributions (M rDs) and the sizes of CPAPs prepared by various cooking procedures.

Determination of molecular mass distribution of silicone oils by supercritical fluid chromatography, matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their off‐line combination. J. Chmelík, J. Planeta, P. Řehulka and J. Chmelík. Journal of Mass Spectrometry, 2001; 36: 760–770

AbstractThe original article to which this Erratum refers was published in Journal of Mass Spectrometry 36(7) 2001, 760–770

Determination of molecular mass distribution of silicone oils by supercritical fluid chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry and their off-line combination.

Silicone oil samples were characterized by supercritical fluid chromatography (SFC), matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI--TOF MS), and their off-line combination. SFC was used to separate samples of silicone oils on micropacked capillary columns. The fractions for the identification studies were obtained from SFC runs at defined time intervals, when the restrictor was pulled out from the chromatographic flame ionization detector (FID) and inserted into a glass vial with acetone. MALDI--TOF MS was used for the identification of individual oligomers in the fractions separated. The molecular mass distributions determined based on SFC and MALDI--TOF MS measurements were compared. From this comparison, it follows that the results are in good agreement. However, certain differences were observed: MALDI--TOF MS was capable of detecting somewhat larger oligomers than the SFC-FID, but the lower molecular mass oligomers were not present in the MALDI spectra. Differences in the region of lower molecular masses can be explained by evaporation of the more volatile low molecular mass oligomers resulting from heating of the sample during the MALDI--TOF MS measurements as a result of the absorption of the laser shot energy. The fact that no high mass discrimination effects of the MALDI--TOF MS measurements, compared with SFC, were observed is very promising for further applications of MALDI--TOF MS in characterizing synthetic polymers of moderate polydispersity.

Determination of molecular mass distribution of κ-carrageenan and xanthan using asymmetrical flow field-flow fractionation

Flow field-flow fractionation combined with multi-angle laser light scattering was used to determine the molar mass distribution of κ-carrageenan and xanthan gum. κ-Carrageenan was studied above and below the order–disorder transition temperature. The molar mass of the helical form was approximately double that of the coil form in agreement with previously observed data obtained by GPC/MALS. The hydrodynamic radius was found to be lower for the ordered state suggesting that FFFF theory is not correct for rod-like polymers. For xanthan gum it was found that measurements had to be performed at a very low polymer concentrations. Above 0.4 mg/ml chromatograms showed a number of peaks, both in the RI and the LS spectra. Below 0.4 mg/ml, however, chromatograms with one well defined peak were obtained. No significant difference in the calculated weight average molar mass was observed between the ordered state (25°C) or if the analysis was performed at the midpoint of the order–disorder transition (50°C), but a shoulder in the differential weight fraction at the high molar mass part was observed for the ordered state. This might indicate the presence of aggregated xanthan gum molecules.

96/05690 Solubility limitations in the determination of molecular mass distributions of coal liquefaction and hydrocracking products: 1-methyl-2-pyrrolidinone as mobile phase in size exclusion chromatography

96/05690 Solubility limitations in the determination of molecular mass distributions of coal liquefaction and hydrocracking products: 1-methyl-2-pyrrolidinone as mobile phase in size exclusion chromatography

Solubility Limitations in the Determination of Molecular Mass Distributions of Coal Liquefaction and Hydrocracking Products: 1-Methyl-2-pyrrolidinone as Mobile Phase in Size Exclusion Chromatography

The use of tetrahydrofuran (THF) as mobile phase in size exclusion chromatography (SEC) has been found to lead to partial loss of sample and to give anomalous results in the characterization of a liquefaction extract and its hydrocracking products. The problem has been resolved by using NMP (1-methyl-2-pyrrolidinone) as mobile phase in SEC, showing significant fractions of sample eluting at the exclusion limit of an identical SEC column. This fraction has not previously been observed in SEC chromatograms obtained in THF. Comparison of SEC chromatograms obtained by UV-absorption and UV-fluorescence detection (in NMP) suggests that the material observed at the exclusion limit of the column corresponds to larger, more complex polynuclear aromatic ring systems than those present in material separated by the column. In NMP, samples produced during progressively higher temperature hydrocracking experiments eluted, as expected, at longer times, indicating progressive molecular size reduction with increasing inte...

Analysis of Polyethers by Isocratic HPLC with Universal Detectors IV. Comparison of Size Exclusion Chromatography and Liquid Adsorption Chromatography for the Analysis of Polypropylene glycols)

Abstract Liquid adsorption chromotography (LAC) on an analytical scale, as well as on a semi-preparative scale is used for the analysis of polypropylene glycols), (PPG), and its performance for the determination of molecular mass distributions was compared with that of size-exclusion chromatography (SEC). Semi-preparative LAC provides monodisperse standards of PPG up to a molecular mass of 1400, which are used to establish an accurate SEC calibration. The influence of preferential solvation in LAC is studied and a correction method using two universal detectors (density and refractive index) is presented.

Characterization of polymer molecular mass distribution from rheological measurements

AbstractVarious methods for the determination of molecular mass distribution from rheological measurements of polymer melts are introduced. Shear viscosity, entrance pressure loss, recoverable shear, and in particular the dynamic viscoelasticity data G' and G” are discussed as analytical tools to evaluate the molecular mass distribution. Well characterized samples and homologous series of the polymers PS, PE‐HD, PP, and PTFE were measured to check the methods. Precise and reliable results can be obtained by calculating the molecular mass distribution from the frequency dependence of the storage modulus.

Determination of molecular mass distributions of whey protein hydrolysates by high-performance size-exclusion chromatography

Two high-performance size-exclusion chromatographic columns (Superose-12 HR 10/30) were compared for their use in the determination of the molecular mass ( M r) distribution of whey protein hydrolysates. For calibration 21 reference compounds of known M r (ranging from 500 to 68 000) were used by applying two procedures for least-squares curve fitting. Based on the calibration graphs constructed, three apparent- M r regions were arbitrarily assigned: M r(app) <5000, 5000-10 000 and > 10 000. Different results for the M r distributions of the whey protein hydrolysates were obtained with the two columns. This was mainly due to a difference in peak resolution, which was better for the Superdex-75 column in the M r region relevant for the major whey proteins and their hydrolysates. The results were also dependent on the mode of calibration curve fitting used.

Application of gel permeation chromatography to the determination of molecular mass distribution of aliphatic polyamides

Conditions have been found for determining by gel permeation chromatography the molecular mass distribution of polyamide-66 in the form of the corresponding fluoroacetyl derivative. The course of the reaction between polyamide-66 and trifluoracetanhydride was followed by IR spectroscopy. Variation in the molecular mass distribution of PA-66 samples of different molecular mass treated at elevated temperatures either individually or in mixture was studied in order to evaluate possible exchange reactions.

Errors in the determination of molecular mass distributions of coal derivatives by size-exclusion chromatography

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTErrors in the determination of molecular mass distributions of coal derivatives by size-exclusion chromatographyKeith D. Bartle, Derek G. Mills, Michael J. Mulligan, Ifeanyi O. Amaechina, and Norman. TaylorCite this: Anal. Chem. 1986, 58, 12, 2403–2408Publication Date (Print):October 1, 1986Publication History Published online1 May 2002Published inissue 1 October 1986https://doi.org/10.1021/ac00125a011RIGHTS & PERMISSIONSArticle Views130Altmetric-Citations54LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (748 KB) Get e-Alerts Get e-Alerts

Application of the Π‐theorem to the determination of molecular mass distribution in individual unfractionted samples. IV. Final considerations

AbstractData on the concentration effect in GPC and simulation data on errors, resulting from the usual assigning of molecular masses to GPC peaks are presented. Discussion of the data and of the previously published ones show, that the sedimentation velocity method is more suitable for the title determination than GPC.

Application of the π‐theorem to the determination of molecular mass distribution in individual unfractionated polymer samples. III. Processing of GPC diagrams accounting for the cut‐off effects

AbstractAn iterative procedure for evaluating the elution volume ‐ molecular mass relationship in individual unfractionated samples, departing from independently determined Mw and Mn values with the corresponding cut‐off effects was developed. It yielded good agreement with experimental data for polystyrene and with literature data for poly(vinyl chloride) and poly(propylene oxide).

Application of the π‐theorem to the determination of molecular mass distribution in individual unfractionated polymer samples. II. Processing of sedimentation diagrams accounting for the cut‐off effects

AbstractBy means of experimental data for polystyrene and polycarbonate samples, the necessity of accounting for the cut‐off effects was shown. An iterative procedure for evaluating the s‐M relation in individual unfractionated samples, departing from independently determined M̄w and M̄n values with the evaluated corresponding cut‐off effects was developed and it yielded good agreement with experimental data.