Taylor dispersion analysis of mixtures

Area of Science:

• Polymer science
• Analytical chemistry
• Physical chemistry

Background:

• Taylor dispersion analysis (TDA) is a rapid technique for determining hydrodynamic radii.
• Non-separative methods like TDA yield an average diffusion coefficient for molecular mixtures.

Purpose of the Study:

• To establish consistent equations for average values obtained by TDA with linear response detectors.
• To compare TDA-derived average diffusion coefficients with those from dynamic light scattering (DLS) for various polymer distributions.

Main Methods:

• Developed theoretical equations for TDA in mixtures with linear detectors.
• Conducted TDA experiments using mixtures of small molecules and polymer standards.
• Compared TDA results with z-average (D(z)) and weight-average (D(w)) diffusion coefficients from DLS for monomodal and bimodal distributions.

Main Results:

• Excellent agreement was found between theoretical predictions and experimental TDA data for mixtures.
• For monomodal, low polydispersity samples (I=1.15), TDA-derived coefficients closely matched D(w).
• Significant differences (up to 35%) were observed between TDA and D(w) for highly polydisperse (bimodal) samples.

Conclusions:

• TDA provides a value close to D(w) for low polydispersity samples.
• TDA's average diffusion coefficient can deviate substantially from D(w) for polydisperse samples.
• TDA with a mass concentration detector yields results closer to D(w) than DLS-derived D(z) for mixtures.