Ultrastyragel columns curves

Figure 3. Individual Ultrastyragel column calibration curves.

Determination of Pore Size Distributions. The shape and range of a GPC calibration curve are, in part, a reflection of the pore size distribution (PSD) of the column packing material. A consideration of the nature of PSDs for the ULTRASTYRAGEL columns to be used in this work is therefore appropriate. The classical techniques for the measurement of PSDs are mercury porisimetry and capillary condensation. The equipment required to perform these measurements is expensive to own and maintain and the experiments are tedious. In addition, it is not clear that these methods can be effectively applied to swellable gels such as the styrene-divinylbenzene copolymer used in ULTRASTYRAGEL columns. Both of the classical techniques are applied to dry solids, but a significant portion of the pore structure of the gel is collapsed in this state. For this reason, it would be desirable to find a way to determine the PSD from measurements taken on gels in the swollen state in which they are normally used, e.g. a conventional packed GPC column. 

Figure 1. Typical calibration curves for lOOA, lO A Ultrastyragel columns.

Figure 5 Scheme for prediction (simulation) of the calibration curve for a column set consisting of two 500A and one lO A Ultrastyragel columns (see text for details). 

In Figure 7, the predicted cumulative PSD is compared with the actual curve for the column set. It should be noted that the prediction is based on data from one 500A and one lO A ULTRASTYRAGEL column which had been calibrated in toluene. (Previous work (19,42) has demonstrated that equivalent PSDs are obtained with several eluents including chloroform, methylene chloride, THF, and toluene.) Neither of these columns was Included in the actual column set, which was independently calibrated in THF using a different instrument. Reasonably... 

Figure 11. Predicted (smooth curve) and experimental (boxes) cumulative PSD for a lO A Ultrastyragel column.

Figure 12. Predicted (smooth curve) cumulative PSD for a IO a Ultrastyragel column, determined incorrectly due to failure to convert log (MW) values to log 0. Experimental cumulative PSD (boxes) is shown for comparison.

Molecular weights were determined by gel permeation chromatography (GPC) using a Waters HPLC system equipped with noodel 510 pump. Waters model 717 autosampler, model 410 refractive index detector, and model T-50/T-60 detector from Viscotek Corporation with 500, 10, 10 and 10 A ultrastyragel columns in series. Trisec GPC software version 3 was used for calculations. Chloroform was used as the eluent at a flow rate of 1.0 mL per minute. Sanq>le concentrations of 0.2 % wt/vol and injection volumes of 100 )XL were used. Molecular weights were determined based on a conventional calibration curve generate by narrow molecular weight polystyrene standards obtained from Aldrich chemical conq>any. 

FIGURE 5-37. Calibration curve for some low-molecular-weight pharmaceutical compounds. Column 100 A Ultrastyragel 7.8 mm ID x 60 cm (two columns). (Reprinted from reference 9 with permission.)... 

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