Molecular Weight Analysis

Shifts in molecular weight following sterilization were assessed by means of gel permeation chromatography (GPC). The samples were dissolved in tetrahydrofuran (THF) prior to analysis so as to obtain a final concentration of 1 mg/mL. The Dionex Ultimate 3000 HPLC system with a diode array and a Varian LC-385 ELSD detector was used for analysis purposes with a polymeric Phenomenex Phenogel 1E4 GPC column with a length of 30 cm with an i.d. of 4.6 mm and particle size of 5 μm. Pure THF of HPLC quality was used as the mobile phase, the flow rate of which was set at 1 mL/min for each sample. The chromatographs were recorded using a Varian LC-385 ELSD detector for a total of 23 min. The temperature of the nebulizer and the evaporator was set at 80 °C and the nitrogen flow rate at 1.1 mL/min. The injection volume of the dissolved polymers was set at 30 μL.

The change in the molecular weight was evaluated from the shift of the maximum peak of the chromatogram representing the most numerous molecular weight in the sample. A peak shift toward longer elution times corresponded with decreasing molecular weight.