What does diffusion NMR measure?
Gradients encode molecular displacement. For free monoexponential diffusion, S(b) = S₀ exp(−bD). The b value depends on sequence timing and gradient shape and amplitude. Gradient percentage alone is not sufficient for absolute D.
What does DOSY add?
It associates spectral signals with diffusion coefficients. Overlap, exchange and noise may limit resolution; sharing a ppm region does not establish identity.
From D to Rh and molecular weight
Hydrodynamic conversion requires temperature and viscosity, and conversion to mass requires a system-appropriate calibration. Empirical concentration parameters should not be forced to reproduce an expected mass.
Internal references and temperature
Check the added standard, its signal and conditions before using it. TTMS is not automatically interchangeable with TMS or TSP. Retain acquired TE and reference temperature, without duplicate thermal normalization.
Inversion and regularization
Distributions are not unique in noise. Inspect fits and residuals, grid sensitivity and regularization. In TRAIn, termFac is a termination factor, not a generic Tikhonov λ; L-curve reasoning does not transfer unchanged between methods.
Reading and provenance
Consult the methodological publications and the parameter record for each analysis.