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Analytica Chimica Acta (v.604, #1)
Contribution of flow field flow fractionation with on line static and dynamic light scattering to the study of hydrosoluble polyelectrolyte complexes by Didier Le Cerf; Sébastien Simon; Jean-François Argillier; Luc Picton (pp. 2-8).
Water soluble polyelectrolyte complexes (PECs) formed between polyaspartate (anionic polymer) and poly(trimethylammonium propyl methacrylamide chloride) (cationic polymer) were studied by flow field flow fractionation with on-line coupling multi-angle laser light scattering–quasi elastic light scattering–differential refractive index determination (F4/MALLS/QELS/DRI). The separation technique permits to characterize polydisperse PECs. The molar mass of the polycation (PC) influences the stiffness of the PECs and the proportion between single PECs (i.e. nPA/1PC) and multiple PECs (i.e. nPA/n’PC). High ionic strength with NaCl (>0.1M) tends to break the multiple PECs while CaCl2 destroys PECs and leads to the formation of complexes polyaspartate/Ca2+. The studied PECs can be used as inhibitors to the calcite formation in the drilling fluids.
Keywords: Polyelectrolyte complexes; Flow field flow fractionation; On line light scattering; Polyaspartate; Calcium ions
Estimation of the band broadening parameters in single detection size-exclusion chromatography: A comparative study of various column combinations by Irene Schnöll-Bitai; Jorge Vega; Christoph Mader (pp. 9-17).
Alternative approaches for the determination of band broadening in size-exclusion chromatography based on the use of exponentially modified Gaussian (EMG) functions were used to experimentally investigate the performance of two different column sets. In both cases, the columns were combined in order to cover the complete fractionation range (from 103 to 5×106gmol−1), which is of interest in many applications. When analyzing experimental chromatograms the question of proper data treatment (especially the necessary smoothing routines) became obvious and is discussed accordingly. First results indicate that the exponential decay time of the EMG decreases and the standard deviation of its Gaussian component slightly increases (or remains almost constant) with increasing retention volumes. As a consequence, the total variance and the asymmetry of the EMG both decrease with the retention volume. A favorable agreement with independent experimental results (obtained by other researchers on the basis of analyzing ultra narrow standards) was found. Additionally, the skew was also investigated as a function of the retention volume and the trend was found to be in concordance with the predictions of theoretical models. The comparison with theoretical models is also discussed.
Keywords: Size-exclusion chromatography; Band broadening; Exponentially modified Gaussian functions
Analytical strategies for the quality assessment of recycled high-impact polystyrene: A combination of thermal analysis, vibrational spectroscopy, and chromatography by Francisco Vilaplana; Amparo Ribes-Greus; Sigbritt Karlsson (pp. 18-28).
Various analytical techniques (thermal analysis, vibrational spectroscopy, and chromatographic analysis) were used in order to monitor the changes in polymeric properties of recycled high-impact polystyrene (HIPS) throughout mechanical recycling processes. Three key quality properties were defined and analysed; these were the degree of mixing (composition), the degree of degradation, and the presence of low molecular weight compounds. Polymeric contaminations of polyethylene (PE) and polypropylene (PP) were detected in some samples using differential scanning calorimetry (DSC). Vibrational spectroscopy showed the presence of oxidised parts of the polymeric chain and gave also an assessment of the microstructure of the polybutadiene phase in HIPS. The presence of low molecular weight compounds in the HIPS samples was demonstrated using microwave-assisted extraction followed by gas chromatography–mass spectrometry (GC–MS). Several volatile organic compounds (VOCs), residues from the polymerisation, additives, and contaminations were detected in the polymeric materials. Styrene was identified already in virgin HIPS; in addition, benzaldehyde, α-methylbenzenaldehyde, and acetophenone were detected in recycled HIPS. The presence of oxygenated derivates of styrene may be attributed to the oxidation of polystyrene (PS). Several styrene dimers were found in virgin and recycled HIPS; these are produced during polymerisation of styrene and retained in the polymeric matrix as polymerisation residues. The amount of these dimers was highest in virgin HIPS, which indicated that emission of these compounds may have occurred during the first life-time of the products. This paper demonstrates that a combination of different analytical strategies is necessary to obtain a detailed understanding of the quality of recycled HIPS.
Keywords: Recycling; Quality analysis; High-impact polystyrene; Degradation; Thermal analysis; Vibrational spectroscopy; Chromatographic techniques
Analytical screening of polyadipates and other plasticisers in poly(vinyl chloride) gasket seals and in fatty food by gas chromatography–mass spectrometry by Z. Ežerskis; V. Morkūnas; M. Suman; C. Simoneau (pp. 29-38).
Fourteen poly(vinyl chloride) (PVC) gasket seals and 15 samples of pesto, tomatoes sauces, olive oil and olives in oil were analysed for the additives and plasticisers. The systematic screening of the representative samples revealed that epoxidised soybean oil (ESBO) was the principal plasticiser in eight gaskets and the concentrations of the substance ranged from 15% to 42%. Diisodecyl phthalate (DIDP) as main plasticiser was revealed in three samples and the amount ranged from 37 to 41%. Polyadipate was added in four samples at 16–46%. The concentration of ESBO exceeded 60mgkg−1 in three food samples with extreme at 281.9mgkg−1 and average 61.3mgkg−1. Di-(2-ethylhexyl) phthalate (DEHP) was detected in six food samples and it ranged from 2.5 to 8.7mgkg−1. The concentration of DEHP exceeded SML (3mgkg−1) in five cases. The concentration of total polyadipate (PA) was 16.3mgkg−1 in average. All eight positive food samples for total PA showed the concentrations below SML (30mgkg−1), which are specified for the fraction of polyadipates lower than 1000Da. The migration rate of polyadipate in the food ranged from 1 to 7%. At such low transfer rate the polyadipates could be promising plasticisers for PVC gasket seals used in food industry.
Keywords: Epoxidised soybean oil (ESBO); Phthalates; Sebacates; Polyadipates; Poly(vinyl chloride) gasket seals; Fatty food; Gel permeation chromatography; Gas chromatography/mass spectrometry (GC/MS)
A data base for polymer chromatography: Dependence of interaction parameters on mobile phase composition by Bernd Trathnigg; Muhammad Imran Malik; Otto Jamelnik; Nguyen Viet Cuong (pp. 39-44).
In chromatography of polymers, retention is determined by the characteristic volumes of the column (pore volume and interstitial volume), the pore diameter, and the interaction parameter. While the influence of the pore diameter is predominant in size exclusion chromatography, the key parameters in liquid adsorption chromatography are the interaction parameter and the pore surface of the column. It is shown, that the retention behaviour of polymers in liquid adsorption chromatography (LAC) can be predicted very well using the accessible volume and pore surface of the column, which can be determined very easily, and the interaction parameters from a data base.
Keywords: Polymers; Liquid chromatography; Adsorption; Interaction parameter; Pore surface; Prediction
Analytical characterisation of glutardialdehyde cross-linking products in gelatine–gum arabic complex coacervates by Elisabet Fuguet; Chris van Platerink; Hans-Gerd Janssen (pp. 45-53).
Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industry for controlled release of actives and flavour compounds. In order to be able to predict the behaviour and the release characteristics of the microcapsules, a better understanding of the nature and extent of the cross-linking reaction is needed.Several analytical techniques were applied for the characterisation of glutardialdehyde (GDA) cross-linked encapsulates made of gelatine and gum arabic. To allow the use of sensitive, high-resolution methods such as chromatography and mass spectrometry, the sample first had to be hydrolysed. In this way, a mixture of amino acids, small peptides and the cross-link moieties was obtained. High-resolution liquid chromatography coupled to high-resolution mass spectrometry (HPLC–MS) was applied to detect possible cross-link markers through a comparison of HPLC–MS mass-chromatograms obtained for cross-linked and non-cross-linked coacervates. HPLC–MS/MS was used to identify the species responsible for the differences. Cross-linking occurred between GDA molecules and lysine and hydroxylysine ɛ-amino groups, and up to eight cross-link products of different nature could be identified. They included pyridinium ions and Schiff bases, and also unreacted GDA condensation products. Next, based on the insight gained in the possible chemical structures present in the cross-link markers, methods for selective labelling of these functionalities were employed to allow easier detection of related reaction products. Both liquid chromatography (LC) and gas chromatography (GC) were used in these experiments. Unfortunately, these approaches failed to detect new cross-link markers, most likely as a result of the low levels at which these are present.
Keywords: Glutardialdehyde; Complex coacervates; Cross-linking; Derivatisation; HPLC–MS; Gelatine
Towards quantification of butadiene content in styrene–butadiene block copolymers and their blends with general purpose polystyrene (GPPS) and the relation between mechanical properties and NMR relaxation times by Nikolaus Nestle; Walter Heckmann; Helmut Steininger; Konrad Knoll (pp. 54-61).
The properties of styrene–butadiene–styrene (SBS) block copolymers do not only depend on the butadiene content and the degree of polymerisation but also on their chain architecture. In this contribution we present the results of a low-field time domain (TD) NMR study in which the transverse relaxation behaviour of different SBS block copolymers was analysed and correlated with findings from mechanical testing on pure and blended materials and transmission electron microscopy data which provide information on the microphase separation.The results indicate that while a straightforward determination of the butadiene content as in blended materials like ABS is not possible for these materials, the TD-NMR results correlate quite well with the mechanical performance of blends from SBS block copolymers with general purpose polystyrene (GPPS), i.e. industrial grade homopolymer polystyrene. Temperature-dependent experiments on pure and blended materials revealed a slight reduction in the softening temperature of the GPPS fraction in the blends.
Keywords: Styrene–butadiene block copolymers; Nuclear magnetic resonance (NMR); Relaxation; Polystyrene; Microphase separation; Butadiene
Numerical optimization of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: Application to synthetic polymer molecular mass distribution measurement by W.E. Wallace; C.M. Guttman; K.M. Flynn; A.J. Kearsley (pp. 62-68).
A novel approach is described for the selection of optimal instrument parameters that yield a mass spectrum which best replicates the molecular mass distribution of a synthetic polymer. The application of implicit filtering algorithms is shown to be a viable method to find the best instrument settings while simultaneously minimizing the total number of experiments that need to be performed. This includes considerations of when to halt the iterative optimization process at a point when statistically-significant gains can no longer be expected. An algorithm to determine the confidence intervals for each parameter is also given. Details on sample preparation and data analysis that ensure stability of the measurement over the time scale of the optimization experiments are provided. This work represents part of an effort to develop an absolute molecular mass distribution polymer Standard Reference Material.
Keywords: Implicit filtering; Instrument optimization; Objective function; Standards; Stochastic gradient approximation
Depolymerization behavior of thermoplastic poly(urethane) (TPU) and its dependence on initial molecular weight by W.W.G.J. van Pelt; J.G.P. Goossens (pp. 69-75).
The quantitative and qualitative depolymerization behavior of thermoplastic poly(urethane) (TPU) consisting of 4,4′-methylenediphenyldiisocyanate (MDI), 1,6-hexanediol (HD) and 1-hexanol (HEX) was described using temperature-modulated differential scanning calorimetry and Fourier transform infrared (FT-IR) spectroscopy. The depolymerization behavior could be altered by lowering the starting molecular weight. This resulted not only in a higher ceiling temperature, but also in a faster decrease of the molecular weight as a function of temperature once the depolymerization has started. The increase in the ceiling temperature for low molecular weight TPUs is attributed to the lower entropy of polymerization for these compounds compared to high molecular weight TPUs.
Keywords: Depolymerization; Fourier transform infrared spectroscopy; Temperature-modulated differential scanning calorimetry; Polyurethanes
Smart Immobilization of oligopeptides through electrochemical deposition onto surface by Hiroaki Sakamoto; Shinya Ikeno; Tamaki Kato; Norikazu Nishino; Tetsuya Haruyama (pp. 76-80).
A novel method for electrochemical molecular immobilization has been developed. Molecular immobilization on an electroconductive material surface is achieved by genetic and chemical introduction of a tag. The immobilization reaction is based on the remarkable phenomenon of neutral metal complex formation on a redox interface. For electrochemical immobilization, a metal coordinative peptide (EC tag) is introduced to the target molecule and is coordinated with a divalent metal ion. In the electrochemical immobilization process, the coordinated metal in the oligopeptide is reduced to the zero-valent metal state and is deposited on the electroconductive substrate. In the present study, we exploit our previous findings to carry out electrochemical peptide immobilization. This immobilization process can be modulated by an applied potential. Although the immobilized peptide is tightly attached the substrate, it can be removed by oxidation of deposited metal though application of an oxidation potential. The method can be employed for the immobilization of various molecules, e.g. proteins, peptides, and nano-materials, on electroconductive solid surfaces. The unique advantages of the present molecular immobilization method are the ease of application and the novel molecular modulations that are achievable.
Keywords: Immobilization; Surface modification; Peptide; Protein; Nano-particle; Electrochemical
Isolation and identification of inulooligosaccharides resulting from inulin hydrolysis by Sébastien N. Ronkart; Christophe S. Blecker; Hélène Fourmanoir; Christian Fougnies; Claude Deroanne; Jean-Claude Van Herck; Michel Paquot (pp. 81-87).
In this study, inulooligosaccharides (F n-type inulin) resulting from the endo-inulinase hydrolysis of globe artichoke inulin were purified and characterized. The aim was to produce F n oligomer standards with the intention of identifying them in the complex inulin chromatogram. Inulin was extracted from globe artichoke and presented a high average degree of polymerization (DP) of about 80 as determined by high-performance anion exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). This inulin was hydrolyzed by a commercial endo-inulinase yielding a product with a very high F n/GF n molecule ratio, thus limiting the interference of GF n during the purification process. High-performance size exclusion chromatography was used to individually isolate and collect each retention peak corresponding to a specific oligomer. The purity of these fractions was checked by HPAEC-PAD and showed that relatively pure molecules were produced. Electrospray ionization mass spectrometry allowed the molecular weight determination of these purified oligomers and ascertained their DP as F2, F3 and F4. These F2–4 standards were used with glucose, fructose, sucrose and GF2–4 (commercially available) to spike commercial oligofructose products in order to determine the elution profile in the HPAEC-PAD chromatogram.
Keywords: Inulin; Hydrolysis; Globe artichoke; Endo-inulinase; Purification; Elution profile