Quantitative analysis of polymer mixtures in solution by pulsed field-gradient spin echo NMR spectroscopy

Area of Science:

• Analytical Chemistry
• Nuclear Magnetic Resonance Spectroscopy
• Materials Science

Background:

• Pulsed Field-Gradient Spin Echo (PGSE) NMR is valuable for mixture analysis by measuring diffusion coefficients.
• Quantifying mixtures with spectral overlap using PGSE NMR is challenging due to relaxation effects.
• Previous methods by Antalek and Barrère et al. utilized DECRA analysis with different approaches to handle relaxation.

Purpose of the Study:

• To develop an alternative quantification approach for PGSE NMR that explicitly incorporates relaxation effects.
• To improve the accuracy of mixture fraction determination, especially in cases of significant spectral overlap.
• To validate the proposed method using model binary and ternary mixtures.

Main Methods:

• Analysis of the PGSE signal attenuation profile using a generalized Stejskal-Tanner equation.
• Explicit inclusion of T1 and T2 relaxation effects within the Stejskal-Tanner equation.
• Simultaneous determination of fractions, diffusion coefficients, and relaxation times from multiple PGSE datasets (up to 6) with varying diffusion delays.

Main Results:

• The developed method accurately quantifies mixture fractions, achieving errors below 3%.
• The approach is effective even for mixtures with complete spectral overlap.
• Demonstrated success on model binary and ternary mixtures of polystyrene using a convection-compensating double stimulated echo (DSTE) sequence.

Conclusions:

• The proposed PGSE NMR quantification method offers high accuracy and robustness, overcoming limitations of spectral overlap.
• Explicitly modeling relaxation effects provides a more reliable approach for mixture analysis.
• This technique enhances the utility of PGSE NMR for complex mixture characterization.