A method for determining B1 field inhomogeneity. Are the biases assumed in heteronuclear relaxation experiments usually underestimated?

We describe a method allowing the determination of the effective B1 field amplitude distribution in a high-resolution NMR spectrometer. This method which can be adapted to almost any sequence, essentially consists of a mutation followed by a purging B0 gradient pulse. Experimental results obtained with this approach are described in homonuclear and heteronuclear cases. The experimental distributions are used to estimate the biases induced by B1 inhomogeneity, as well as the loss of RF power on heteronuclear transverse self-relaxation rate determination. In this type of measurement, the experimental biases induced on the intensities can be as large as 5% for long mixing times. Copyright 1999 Academic Press.