Influence of peak-broadening and interdetector volume error on size-exclusive chromatographic analysis with dual viscometric-concentration detection using the universal calibration method

The effect of peak-broadening and error in interdetector volume on the loca l calibration curve and experimental molecular-mass averages obtained by si ze-exclusion chromatography (SEC) with dual concentration/viscosity detecti on, and determination of molecular mass using the universal calibration (UC ) method, is theoretically examined using a polymer sample with a molecular -mass distribution (MMD) approximated by the log-normal function. Although peak-broadening is often neglected, its effect on the slope of the local ca libration curve and, consequently, on the experimentally obtained values of the weight-to-number average ratio is large. To obtain the right values of these parameters, a numerical correction is usually recommended. While usi ng the UC method, the relationships between the extent of peak broadening, calibration slopes and interdetector volume are complex and can contribute to the occurrence of undiscovered errors. For this reason, an understanding of this problem, using a model, is necessary. The results of the UC method are compared with those obtained using dual-detection with known Mark-Houw ink-Kuhn-Sakurada parameters (MHKS method), Light-scattering (LS)/ concentr ation detection as well as with the results obtained using conventional cal ibration. Due to peak-broadening, the slope of a local calibration curve an d the weight-to-number average ratio, ((M) over bar (w)/(M) over bar (n))", obtained using the UC method, increase compared to the theoretical values, whereas they decrease using the MHKS or LS methods. The increase when usin g the UC method is even larger compared to evaluation using conventional ca libration. The effect of the error in interdetector volume on the slopes of local calibrations and the weight-to-number average ratios is opposite in the UC method to that found using the MHKS and LS methods. (C) 2001 Elsevie r Science B.V. All rights reserved.