Molecular weight distributions monitoring

The molecular weight distribution of cell wall polysaccharides was estimated by gel filtration with a TOSOH TSK gel G4000 PWXL (7.8 x 300 mm) column equilibrated and eluted with 0.05 M sodium acetate, 0.01 M EDTA, 0.05 M NaCl (pH 5.0) in polyuronide and 0.05 M sodium citrate, 0.1 M NaCl (pH 5.5) in the hemicellulose fraction. Samples (1 mg/ml) of 100 ml were injected. The eluate was monitored by a refractive index detector (Shimadzu R1D-6A, Kyoto, Japan) and collected at the fraction size of 0.4 ml. 

In this study, four Styragel columns were utilized one column had a nominal porosity rating of 10, two colvtmns of 10, and the fourth column of 10 A. The refractometer was maintained at 37°C. A 5 ml syphon was used to monitor a solvent flow rate of 1 ml/min. The instrviment was run at the highest sensitivity setting because the refractive index difference between our solvent and polymer was only moderate and because a number of samples analyzed had a broad molecular weight distribution (MWD). 

Aqueous systems are favourable for the degradation of PVA. Kinetic monitoring of the molecular weight distribution in liquid cultures of mixed microbial... 

Figure 9. Apparent molecular weight distributions representing a homologous series of kraft lignin samples secured by desalting after association and dissociation in aqueous alkaline solutions for (1) 300 h, (2) 144 h and (3) 48 h at 170 gL1 in 1.0 M ionic strength aqueous 0.40 M NaOH (4) 0 h (5) 144 h and (6) 644 h at 0.50 gL 1 in aqueous 0.10 M NaOH. (Sephadex GlOO/aqueous 0.10 M NaOH elution profiles monitored at 320 nm.)...

In conclusion, it can be seen that thermal analysis is able to make a considerable contribution to forensic science. Because of its capability to differentiate between manufacturing lots, it has for years been employed in quality control laboratories to monitor production of polymeric products. Its capability of differentiating between materials of identical chemical composition on the basis of differences in molecular weight distribution and thermal or mechanical history should be a capability quite unique and useful to forensic science. With the advent of second-generation instrumentation, this technique can be usefully extended to the realm of submilligram level analysis. 

By examining the weight-average molecular weight and the molecular weight distribution of the molecules in a polymer, the scientist can better monitor and control the polymerization to produce a better product. Also, by using GPC purchased polymers can be selected to reduce variability and to better control the quality of the final product. 

Eluent from the SEC separation passes through a capillary or capillaries (one, two and four capillary designs are available) and the pressure drop is monitored by a differential pressure transducer. From the pressure drop and the concentration of the sample (obtained from the DRI) the intrinsic viscosity (ri) can be calculated. Molecular weight averages, Mark-Houwink (for polymer branching studies) and molecular weight distribution plots can then be obtained after suitable data treatment. 

Synthesis. The main demand for the synthesis of this new type of liquid crystalline polymer is a high conversion and the absence of any side reactions for both reaction steps. For the first investigations described in this communication IR-spectroscopy was used to determine the conversion. The molecular weight distribution obtained from gel permeation chromatography (GPC) is used to monitor side reactions. 

The molecular weight or, more rigorously, molar mass (M) and molecular-weight distribution (MWD) of a reactive system (shown in Figure 1.6 and discussed in Section 1.1.3) can be monitored via gel permeation chromatography (GPC). The sample is introduced to the... 

The problem, of course, comes from the implicit assumption that the gel matrix has no specific interactions with the soluble polymer, and that the relationship between effective volume and molecular weight is the same for the polysaccharide of interest and the standards. A recent development has been to place instruments which measure molecular weight at the exit of a GPC column, so that the column is used only for fractionation, and a full molecular weight distribution of a polydisperse polymer can be obtained. Viscometers and light-scattering monitors can be so employed, as can on-line electrospray mass spectrometers. The last technique is particularly powerful, since the masses determined by the mass spectrometer are absolute. 

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