A DIFFERENTIAL PRESSURE CAPILLARY VISCOMETER AS A DETECTOR FOR SIZE EXCLUSION CHROMATOGRAPHY

A differential pressure capillary viscometer has been designed and the performance of the viscometer was evaluated. The viscometer was composed of four capillaries and two differential pressure transducers. The viscometer was connected to the size exclusion chromatography (SEC) system. The first capillary was connected before and the second after the sample column, the third and the fourth after the reference column. An empty tubing used as a delay reservoir was connected between the third and the fourth capillaries. The differential pressure between the inlets of the second and the fourth capillaries was measured. The other two capillaries were used for the flow compensation. The linear relationship was obtained between log intrinsic viscosity and log molecular weight (MW) for polystyrenes over the MW ranging from 10(4) to 10(6). The upward deviation from the linearity for the polymers with MW lower than 10(4) and the downward deviation for those higher than 10(6) were observed. The former case was considered to be caused by the different viscosity-MW relationship between polymers and oligomers. The latter case was attributed to the shear degradation of the polymers which occured during passage of the polymer samples through the SEC column.