Biexponential fitting of diffusion-ordered NMR data: practicalities and limitations

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Nuclear Magnetic Resonance (NMR)

Background:

• High resolution diffusion-ordered NMR spectroscopy (HR-DOSY) typically employs monoexponential fitting for signal analysis.
• This method is limited to separating signals that are spectrally well-resolved.
• Overlapping spectral peaks present a significant challenge for accurate diffusion analysis.

Purpose of the Study:

• To investigate the potential of multiexponential fitting for resolving coincident spectral peaks in HR-DOSY.
• To analyze the limitations of biexponential fitting, including signal-to-noise ratio and pulsed-field gradient (PFG) nonuniformity.
• To demonstrate improvements in DOSY spectra by applying biexponential fitting with compensation for PFG distortions.

Main Methods:

• Analysis of diffusional attenuation in pulsed-field gradient stimulated echo spectra.
• Application and evaluation of biexponential fitting models.
• Exploration of instrumental distortions, specifically PFG nonuniformity.
• Development and illustration of compensation strategies for signal decay.

Main Results:

• Monoexponential fitting in HR-DOSY is insufficient for resolving overlapping spectral peaks.
• Biexponential fitting shows potential for separating coincident signals but is sensitive to noise and PFG distortions.
• Compensating for PFG nonuniformity significantly improves the quality of DOSY spectra obtained via biexponential fitting.

Conclusions:

• Multiexponential fitting, particularly biexponential fitting, offers a pathway to resolve overlapping signals in HR-DOSY.
• Addressing instrumental distortions like PFG nonuniformity is crucial for the successful application of advanced fitting methods.
• Improved signal separation in diffusion NMR enhances analytical capabilities for complex mixtures.