Gel chromatographic separation

In the third section, a gel chromatographic separation method will be set up in order to enable the evaluation of the changes of molecular weight distribution of the HEC substrate due to a slow cellulolysis. In... 

Gel Chromatographic Separation of HEC and Determination of the Molecular Weight Distributions. Introduction. In order to evaluate the dispersion of the HEC, it is necessary to determine some distribution parameters. 

One of the most important advantages of gel chromatographic separations could not be used—namely, the calibration of the column using narrow-molecular-weight standard substances to determine the a... 

Table I. Fractionation Data of HEC After Gel Chromatographic Separation on Sepharose C14B (Pharmacia Fine Chemicals AB, Uppsala, Sweden)...

Fractionation Data and Distribution Analysis of HEC After One Hour of Cellulase Attack. The results of the gel chromatographic separation of HEC after one hour of enzymic hydrolysis are given in Table II. These fractionation data did not correspond to any of the distribution functions mentioned by Peebles (41) and by Tung (42). In the middle of the distribution it corresponded to the Lansing-Kraemer distribution functions, but deviations occurred at the low- and high-molecular-weight ends. 

An earlier procedure reported from this laboratory for the isolation of sulfides was based on the selective oxidation of the sulfides to the sulfoxides with photoexcited singlet oxygen followed by silica gel chromatographic separation of the sulfoxides (9). Reduction of the isolated sulfoxides back to the sulfides and a subsequent chromatographic purification resulted in the isolation of the sulfides as a pale yellow oil. However, when the sulfur is in a five-membered ring, the photooxidation may lead to side reactions (22). Therefore, other oxidation methods had to be explored. 

Determination of Response Factors. Speciflc response factors were obtained by injecting known concentrations of saturates and aromatics fractions obtained by clay-gel chromatographic separation of various gas oil fractions as well as residua boiling above 510°C. All of the clay-gel saturates fractions showed the presence of some aromatic impurities (2-20%) by HPLC. This was particularly true of the saturates obtained from the 510°C residue samples. Also, the aromatics fractions showed the presence of some saturates (2-3%) by HPLC. The response factors for these saturates and aromatics fractions are listed in Table II. Based on the values shown in Table II, the response for the aromatics was about 1.7 times that for the saturates. The ratio of the response factors for the gas oil fractions differs from the ratio for the residuum samples by about 6%, relative. 

Comparison of the HPLC Technique with Clay—Gel Chromatographic Separation. A number of vacuum gas oils were analyzed by preparing solutions in n-heptane at a concentration near 100 mg/mL. These samples were injected into the HPLC equipment and the concentration of saturates and aromatics calculated from the response factors shown in Table II. The absolute percentages of saturates and aromatics are shown in Table III along with the polar aromatics obtained by subtracting the sum of these from 100%. 

Table V. Comparison of Moving-Wire Detector with the Refractive Index Detector and Clay—Gel Chromatographic Separation (Vacuum Gas Oil)...

The majority of gel chromatographic separations are carried out by elution development (cf.. Chapter 1) of the molecularly dispersed macromolecular solutes through the gel bed packed in a column this case will be considered in the following discussions unless otherwise stated. 

The above simple model of a steric exclusion mechanism was considered by several authors attempting to describe quantitatively the gel chromatographic separation process. Distribution coefficients were expressed on the basis of the model considerations of the dimensions of both the separated molecules and the pores of gel, as well as of the stochastic model approaches (for reviews see e.g.. Refs. 1, 3-6), and also of the thermodynamic reasoning on the changes of conformational entropy of macromolecules due to their transfer from the interstitial volume into the pores in the course of separation [7]. However, besides the steric exclusion from the pores, at least two other size-based mechanisms are operative in the ideal gel chromatography ... 

The nature of particular secondary processes and their influence on the results of gel chromatographic separation are discussed in detail, e.g., in Refs. 6,10,11. 

The secondary processes usually disturb the gel chromatographic separation or complicate the processing of the chromatographic analytical data. That is why it is necessary to remove, or at least to suppress, the secondary processes in common experimental practice by the appropriate choice of the operational variables. For example, the effects of adsorption, thermodynamic partition and incompatibility can be diminished by the choice of gel and eluent, while the ionic effects are suppressed by adding a suitable salt into eluent, and the concentration effects are not important when working with very low sample concentration or when applying the thermodynamically poor solvent as mobile phase. 

The product of a gel chromatographic separation is either a fraction that can be... 

Within certain limits, the majority of operational variables do not determine the results of gel chromatographic separations in a decisive way. Nevertheless, it is advisable to test all variables for each particular system and application in order to obtain optimal and reproducible data. The most common operational variables in gel chromatography are the volume, Uj, and the concentration, C, of the sample applied, both influencing the retention volumes and the separation efficiency. In analytical separations, it is necessary to work with the lowest v, and C allowed by the particular detection system (cf., section 4.6.3.6). The allowed sample volume depends primarily on the volume of the column and is usually several millilitres in the case of... 

Similar relative acceleration was achieved also in the modern preparative gel chromatographic separations. 

Under preparative gel chromatographic separation one understands the preparation of larger fractions that can be utilized either for further characterization by means of independent methods in clinical practice, for the calibration of the instruments, etc. 

Hi) The procedures, where the gel chromatographic separation is combined with other, non-chromatographic, selective physico-chemical processes such as solvation, association, aggregation, precipitation, electrokinetic effects, etc. 

Klimisch, H.-J. and D. Reese Gel chromatographic separation of hydrocarbons, amines and phenols on a polystyrene gel column. Preparative fractionation of cigarette smoke condensate for biological experiments ... 

Gel chromatographic separations and purifications with controlled pore beads. 

Hanada, K., Fujimoto, K., Shimura, M., andYoshioka, K. (1998). Determination of trace amounts of Si and P in iron and steel using gel chromatographic separation followed by ICP-MS. Phys. Status SoMA 167(2), 383. 

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