Comparison of on-line single-capillary and bridge capillary viscometric detectors for size exclusion chromatography

A systematic and thorough comparison is made of a laboratory-built single-capillary viscometer and a bridge viscometer, integrated together into a size exclusion chromatography (SEC) apparatus incorporating a multi-angle laser light scattering (MALLS) photometer and a differential refractometer. It is demonstrated that proper choice of the SEC pump is crucial to realize the potential accuracy of either viscometer design. Random measurement error contributes an order of magnitude greater error in the single-capillary viscometer than in the bridge viscometer, and thus the bridge viscometer gives significantly greater precision in any one measurement. Other sources of error, such as calibration error and stochastic variation from one run to the next, however, reduce the bridge viscometer's greater precision to only about a factor of two greater than the single-capillary design. Two advantages compensating for the laboratory-built single-capillary viscometer's decreased precision are its compactness and its significantly lower cost. By the use of variety of polymers (hyaluronate, poly(vinyl pyrrolidone) and dextran), estimates of scaling laws for both soot-mean-square radius of gyration and reduced viscosity are made, and their accuracies and sources of error assessed.