Polydextran

The second method assumes that the molecular weight calibration curve is linear on a semilog plot and should be employed where universal calibration is not practical as with aqueous SEC. Several variants of these methods involving different molecular weight data for the standards are discussed. The proposed methods have been evaluated using aqueous SEC and polydextran standards and nonaqueous SEC with polyvinylchloride standards. 

Methods based on universal calibration will be illustrated using nonaqueous SEC and broad MWD PVC standards. The and of these standards is known. Methods based on the linear molecular weight calibration will be illustrated using aqueous SEC and broad MTO polydextran standards for which M and My are known. 

Polydextran standards employed in this investigation are listed in Table IV. 

Figure 4. Molecular weight calibration curves for polydextran obtaimd u g linear calibration and two broad M WD standards and by plotting Mrm ( / Mif Mw) vs, peak retention volume ((%) Mrms, (---------) M(v) = 0,37 X exp(—OJ v))...

Table V. Results of Case Study 2 - Linear Calibration with Two Broad MWD Polydextran Standards with Known Mj and...

Figure 6.3 Ultrafiltration membranes are rated on the basis of nominal molecular weight cut-off, but the shape of the molecule to be retained has a major effect on retentivity. Linear molecules pass through a membrane, whereas globular molecules of the same molecular weight may be retained. The table shows typical results obtained with globular protein molecules and linear polydextran for the same polysulfone membrane [8]...

Figure 13.4. Apparent MWs of HS from different environments as determined by SEC [compiled from the data reported by Perminova et al. (2003)]. Bars represent a range of weight-averaged molecular weights determined for different groups of humic materials. Two black dots represent two IHSS standards Suwannee River FA and HA. SEC chromatograms were obtained with column-packing Toyopearl HW-50S using 0.028 M phosphate buffer at pH 6.8 as a mobile phase. Two different sets of standards were used to calibrate the column polystyrene sulfonates (PSS) and polydextrans the upper MW scale corresponds to dextran calibration and the bottom one—to PSS calibration.

There are two classes of stationary phases in SEC, one type for GFC and the other for GPC. Stationary phases for GFC are hydrophilic and include polydextrans, polyvinyl alcohol gel, and silica gel those for GPC are hydrophobic, typically cross-linked, rigid polystyrene-divinylbenzene gels. Generally, columns of 15 to 50 cm length are used, packed with 7- to 10-/t,m particles and with an internal diameter between 0.6 and 0.8 cm. In SEC, unlike in other chromatographic modes, the stationary phase is the primary factor controlling retention. 

Many other substrates have been used for IEC in addition to the polystyrenes. Some are natural products like cellulose, often crosslinked for added rigidity, and others are manufactured like polydextran gels. Most of them can only be used at low pressures, like the polystyrenes just discussed. 

Methylamino-5-(l-methylalIylamino)-l,3,4-thiadiazoIe is an oxidation product of methallibure, a veterinary oestrus regulator. Separation can be achieved by chromatography on alkylated polydextran gel and elution with mixed organic solvents. Metal salts can be removed by complexation with diphenylthiocarbazone (70JPS835). 

Porath and Flodin Cross-linked polydextrans—Gel filtration... 

Lee and Lightfoot [229] developed the theoretical basis of Fl-FFF. This theory has been confirmed by numerous works on the fractionation of model systems, including monodisperse spherical polystyrene latexes and a number of proteins [41,228,229,240], some polydextrans [229], viruses [241], and other spherical particles and macromolecules [242,243]. 

---