Multiple Linear Least-Squares Fits with a Common Intercept: Determination of the Intrinsic Viscosity of Macromolecules in Solution
M. C. Lopez Martinez, F. G. Díaz Baños, A. Ortega Retuerta, José Garcı́a de la Torre · Journal of Chemical Education · 2003
A procedure, based on the least-squares principle for simultaneously fitting two or more linear data sets with a common intercept, is described. Expressions are derived to calculate the common intercept and the slopes. The procedure is applied to several laboratory experiments. Particularly, this procedure is employed in the measurement of the intrinsic viscosity, which expresses the concentration dependence of the viscosity of a dilute polymer solution. The intrinsic viscosity is determined by extrapolation to zero concentration of a polymer quantity that involves the solution viscosity and concentration. The extrapolation can be done by two procedures, associated with the names of Huggins and Kraemer, both yielding the intrinsic viscosity as the common intercept. A numerical procedure, implemented with the computer program VISFIT was devised. This procedure is employed for the data analysis in the determination of intrinsic viscosities.