Highly Accurate Determination of the Delay Volume between the MALS and Differential Refractometer in SEC

Size exclusion chromatography (SEC) equipped with a multi-angle light scattering (MALS) detector has widely been used as the standard analytical equipment for estimating the fundamental characteristics of polymers, such as the weight average molecular weight (Mw) and root-mean-squared radius of gyration. The interdetector delay volume (IDV) between the MALS and differential refractometer (RI) is an important parameter that strongly influences the reliability of the experimental value. However, a reliable determination method has not been published as yet. This paper reports a method for determining the IDV value with high reliability. SEC-MALS measurements were performed for polystyrene (PSt) standard with an Mw ranging from 1.0x104 to 110x104 at different flow rates (U) ranging from 0.1 to 1.0 cm3 min-1 to investigate the effects of U and Mw on IDV value. The band broadening effects within the SEC column are evaluated based on the van Deemter equation, and those occurring between the detectors are discussed. Reliable IDV values are obtained when the theoretical height of the column and the turbulence between the detectors are minimized. The SEC-MALS set up with the reliable IDV value accurately gives the absolute Mw and Mn and differential weight distribution curve for the PSt's with the broad and narrow molecular weight distribution.