Recent Advances in Gel Permeation Chromatography

Gel permeation chromatography (GPC), sometimes referred to as size-exclusion chromatography (SEC), has progressed at an almost explosive rate since its introduction less than two decades ago. One has only to refer to the open literature or thumb through the list of Chromatographic equipment manufacturers anxious to sell their latest innovation to be fully convinced of this fact. Because of the extensive progress in GPC technique and instrumentation, the author had a very difficult time in deciding the scope of this review. Mindful that he may be criticized of being myopic in his presentation of the most significant and recent contributions and guilty of gross omission of important references, the author has nevertheless decided to narrow the scope to three major areas and a few key references. The three major areas to be covered are: (1) data acquisition and processing, (2) high-pressure chromatography and (3) detectors. Extensive progress has been made in the computerization of both data acquisition and data reduction, the latter allowing molecular weight distribution (MWD) and molecular weight averages to be obtained on the sample in a matter of minutes rather than hours or days. The main beneficiaries of the computerization of data acquisition and processing have been those concerned with polymer quality control, for it has liberated them from the drudgery of the manual digitization, integration, and normalization of the chromatograms required to reduce them to a useful format. The hours of monotonous eye-straining work to obtain MWD and molecular weight averages has been reduced to a few seconds of punching a few keys of the data system console. The development of the high-pressure Chromatograph has added a new dimension to GPC, for, when it is combined with a computerized data system, the MWD can be obtained almost in real time in relation, for example, to a characteristic time of a polymerization reactor. In high-speed Chromatograph y under nearly ideal conditions (low-viscosity mobile phase and molecular weight of no more than a few hundred thousand), the MWD can be obtained in a few minutes. This capability allows the use of GPC as on-line process-control equipment. The Chromatograph can be used as part of a “feed-back” loop to control the polymerization conditions to obtain a product of consistent MWD.