4. Acquisition

Time requirement: 10 min Sample: 2 mM sucrose in 90% H₂O/10% DO + 0.5 mM DSS (2,2-dimethyl-2- silapentane-5-sulfonate, sodium salt) + trace of NaN3 against bacteria growth.

The probe-head must be tuned to the sample used. Record a normal ¹H NMR spectrum and center the offset at the water resonance. Load the WATERGATE pulse program. You have to set:

td: 32k sw: 10 ppm o1: on water resonance p1: 90° ¹H transmitter pulse d2: 300 μs g1, g2: sinusoidal-shaped field gradients, 2 ms duration and 5% truncation, with gradient loop counters, ring-down delays (100 μs), lock blanking and gradient coil blanking switches according to the actual instrumentation used. Gradient strength must be adjusted experimentally; gradient strength

5. Processing

Use standard 1D processing as described in Experiment 3.1 with exponential multipli- cation (lb = 0.5 Hz) and a base-line correction.

6. Result

The figure shows the result obtained on an AMX-500 spectrometer with a BGU (10 A) gradient amplifier and a 5 mm inverse z-gradient probe-head. Compared with Experi- ment 6.18 the advantages claimed for this experiment are less convincing in our hands due to base-line roll and phasing problems, which are addressed in Ref. [4].

7. Comments

The sequence is, in principle, a spin-echo experiment in which the 180° pulse is embedded between two pulsed field gradients. After excitation by the first pulse p! the field gradient g1 dephases all coherences. The pulses p2-p7 consist of a binomial se- quence (3a, 9a, 19a, 19a, 9a, 3a, with 26a = 180°).