DOSY Experiments - Emory University

DOSY pulse sequences use the gradient stimulated echo element (or one of its modifications):
In the DOSY experiments the strength of the diffusion-encoding gradient is arrayed and the
diffusion coefficients are calculated according to the Stejskal-Tanner formula:
where S(Gzi) and S(0) are the signal intensities obtained with gradients strengths of Giz and 0,
respectively, D is the diffusion coefficient, γ is the gyromagnetic constant, δ is the gradient pulse
duration and Δ is the diffusion delay.
From the formula alone one can get valuable hints on how to set DOSY-related parameters in
different pulse sequences.
(γδGzi) 2 – gradient pulse area squared
a: nuclei with higher γ are more sensitive to diffusion than the low-γ nuclei. (If possible,
observe 1 H or 19 F, or at least do the diffusion-encoding step on the high-γ nucleus (see
Dbppsteinept).
b: shaping a gradient dramatically reduces its phase encoding efficiency. Although the
VNMR software enables the shaping of gradients on VNMRS or 400-MR spectrometers,
it is not really recommended.
δ – gradient pulse duration
during δ (and the subsequent gradient stabilization delay, gstab) the magnetization is
transverse and subject to T2 relaxation and homonuclear J-evolution. Do not use long δ
values in the presence of large homonuclear couplings or short T2 relaxation times (δ