Analysis of Synthetic Polymers and Rubbers

The signal-to-noise issue in mass spectrometric analysis of polymers

Mass spectrometric approaches to polymer analysis become increasingly ineffective as average molecular weight increases. This perspective explains these fundamental limits of MS for determining molecular weight distribution of high polymers.

Quantification of trans-1,4-polyisoprene in Eucommia ulmoides by fourier transform infrared spectroscopy and pyrolysis-gas chromatography/mass spectrometry

Commercial development of trans-1,4-polyisoprene from Eucommia ulmoides Oliver (EU-rubber) requires specific knowledge on selection of high-rubber-content lines and establishment of agronomic cultivation methods for achieving maximum EU-rubber yield. The development can be facilitated by high-throughput and highly sensitive analytical techniques for EU-rubber extraction and quantification. In this paper, we described an efficient EU-rubber extraction method, and validated that the accuracy was equivalent to that of the conventional Soxhlet extraction method. We also described a highly sensitive quantification method for EU-rubber by Fourier transform infrared spectroscopy (FT-IR) and pyrolysis-gas chromatography/mass spectrometry (PyGC/MS). We successfully applied the extraction/quantification method for study of seasonal changes in EU-rubber content and molecular weight distribution.

Improved matrix-assisted laser desorption/ionisation sample preparation of a partially depolymerised cellulose derivative by continuous spray deposition and interfacing with size-exclusion chromatography

Continuous spray deposition (CSD) of aqueous solutions of partially depolymerised methyl cellulose was found to improve matrix-assisted laser desorption/ionisation (MALDI) sample preparation. One feature was that the sensitivity in MALDI time-of-flight mass spectrometry increased up to an order of magnitude compared with the standard sample preparation method. Another feature was that CSD provided targets for MALDI with homogeneously distributed analyte. This resulted in a more even signal intensity and a higher reproducibility than in the standard method. High-mass discrimination was more pronounced in CSD than in the standard method. Size-exclusion chromatography with aqueous eluent was coupled online to CSD onto matrix-precoated foils. The suitability for determination of the molar mass distribution of methyl cellulose was investigated.

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of partially depolymerised carboxymethyl cellulose

Sample preparation effects in matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) of partially depolymerised carboxymethyl cellulose (CMC) have been investigated. The depolymerisation was either enzymatic or acidic. Fractions of enzymatically depolymerised CMC were collected from size-exclusion chromatography (SEC) and further investigated by MALDI-TOFMS. 2,5-Dihydroxybenzoic acid was used as matrix, dissolved in H(2)O due to the poor solubility of CMC in suitable organic solvents. The samples were dried by two methods, in ambient atmosphere and at reduced pressure. Under reduced pressure the sample spot homogeneity increased. This drying method, however, produced additional adduct peaks in the mass spectra originating from ion exchange on the CMC oligomers. Analysis of CMC could be performed in both negative and positive ion modes. Mass discrimination and variation in ionisation efficiency were demonstrated by comparing mass spectra with SEC data. Measurements of the degree of substitution (DS) were performed on three CMCs with different DS values, which were depolymerised in trifluoroacetic acid. The three CMCs were easily distinguished from one another, but the obtained DS values deviated from the values supplied by the manufacturer.

Qualitative assessment of monomer ratios in putative ionic terpolymer samples by electrospray ionization mass spectrometry with collision-induced dissociation

Collision-induced dissociation in the source of an electrospray (ES) mass spectrometer was employed to characterize putative samples of the ionic terpolymer poly(styrene sulfonate-co-acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid). Qualitative and semi-quantitative information about the monomer content was quickly obtainable from ES spectra, and indicated that some samples contained little or none of one or two expected comonomers. For two representative samples, confirmatory nuclear magnetic resonance (NMR) data were acquired. The NMR experiments required sample clean-up (to remove additives) and long acquisition times (up to 720 min) for 13C NMR. Cleanup also improved the ES results, providing better agreement with the NMR data. However, qualitative and semi-quantitative information was obtainable by ES (but not by NMR) without the cleanup step. Full quantitation of monomer ratios would require suitable standards, but even without such standards the ES measurements provide a rapid (<1 min) means for differentiating these samples (e.g., for process or quality control).

Improvements in pentosan polysulfate sodium quality assurance using fingerprint electropherograms

Complex samples from polymer production, plant extracts or biotechnology mixtures can be characterized by fingerprints. Currently, the standard approach for sample characterization employs near-infrared (NIR) spectroscopy fingerprinting. Up to now, however, fingerprints obtained by chromatography or electrophoresis could only be visually evaluated. This type of inspection is very labor-intensive and difficult to validate. In order to transfer the use of fingerprints from spectroscopy to electrophoresis, spectra-like properties must be obtained through a complete alignment of the electropherograms. This has been achieved by interpolation and wavelet filtering of the baseline signal in the present work. The resulting data have been classified by several algorithms. The methods under survey include self-organizing maps (SOMs), artificial neural networks (ANNs), soft independent modeling of class analogy (SIMCA) and k-nearest neighbors (KNNs). In order to test the performance of this combined approach in practice, it was applied to the quality assurance of pentosan polysulfate (PPS). A recently developed capillary electrophoresis (CE) method using indirect UV detection was employed in these studies [1]. All algorithms were well capable of classifying the examined PPS test batches. Even minor variations in the PPS composition, not perceptible by visual inspection, could be automatically detected. The whole method has been validated by classifying various (n = 400) unknown PPS quality assurance samples, which have been correctly identified without exception.

Protein sizing on a microchip

We have developed a microfabricated analytical device on a glass chip that performs a protein sizing assay, by integrating the required separation, staining, virtual destaining, and detection steps. To obtain a universal noncovalent fluorescent labeling method, we have combined on-chip dye staining with a novel electrophoretic dilution step. Denatured protein-sodium dodecyl sulfate (SDS) complexes are loaded on a chip and bind a fluorescent dye as the separation begins. At the end of the separation channel, an intersection is used to dilute the SDS below its critical micelle concentration before the detection point. This strongly reduces the background due to dye molecules bound to SDS micelles and also increases the peak amplitude by 1 order of magnitude. Both the on-chip staining and SDS dilution steps occur in the 100-ms time scale and are approximately 10(4) times faster than their conventional counterparts in SDS-PAGE. This represents a much greater speed increase due to microfabrication than has been obtained in other assay steps such as electrophoretic separations. We have designed and tested a microchip capable of sequentially analyzing 11 different samples, with sizing accuracy better than 5% and high sensitivity (30 nM for carbonic anhydrase).

Separation and characterization of oligomers by reversed-phase high-performance liquid chromatography: a study on well-defined oligothiphenes

Reversed-phase high-performance liquid chromatography (RP-HPLC) was used for the separation of 3-hexylthiophene oligomers in the range of 3 to 30 monomeric units, while systematically varying stationary and mobile phases. A set of different columns was chosen, covering a broad range of silica types, pore sizes and bonding chemistry. Mobile phases of tetrahydrofuran (THF) combined with water, acetonitrile (ACN) or methanol (MeOH) were used. Although differences between columns were small, a higher selectivity correlated with a lower hydrophobicity parameter from the Galushko column test. The model of Jandera, based on the linear solvent strength model of Snyder, was used to describe the retention of the oligomers in gradient mode. This gave information about selectivities on different stationary phases similar to the hydrophobicity parameter. Contrary to the stationary phase, the mobile phase had a major influence on the selectivity. The THF-water combination gave much higher selectivities compared to THF combined with MeOH or ACN. Using the aqueous mobile phase even enabled separation of different isomers. Determination of thermodynamic parameters for the model compounds showed that retention of the different isomers was mainly determined by the orientation of the side chains at both ends of the chain. An additional repeating unit in the middle of the polymer backbone gave a similar contribution to retention, irrespective of the orientation of its side chain. Three model isomers were separated by preparative RP-HPLC and identified by proton nuclear magnetic resonance spectroscopy. The combination of subsequent preparative size-exclusion chromatography, RP-HPLC and matrix-assisted laser desorption ionization time-of-flight mass spectrometry enabled the identification of the two major oligomeric series in the sample as the regioregular product with one bromine end group and, in smaller amounts, a regioirregular product with two bromine end groups. reserved.

Number-average molecular mass determination of polymeric material by pyrolysis-gas chromatography

The number-average molecular mass of a polymeric material has been determined by pyrolysis-gas chromatography (Py-GC) via end-group analysis. The major advantage of this technique is that no sample preparation is required. The sample is not required to be in the dilute solution form, and the amount of sample needed is approximately 0.5 mg. Phenyl group-terminated polybutadiene systems have been studied as an example. The application of Py-GC to obtain the end-group concentration, the number-average molecular mass and the limitations of this method are discussed in detail. The success of this development elevates the role of Py-GC as an important technique for end-group analysis for the determination of number-average molecular mass.