4. Acquisition

Time requirement: 5 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 NaN; against bacteria growth.

The probe-head must be tuned to the sample used; the temperature should be regulated and controlled to 298 K. Record a normal ¹H NMR spectrum and center the offset at the water resonance. Determine the attenuation for a 90° selective Gaussian pulse of 20 ms (see Exp.7.1) [here 59.5 dB was used] and the 90° hard proton transmitter pulse. Load the WET pulse program. You have to set:

td: 32k sw: 12 ppm o1: on water resonance p1: 81.4° selective Gaussian pulse [20 ms, 59.5 + 0.87 = 60.37 dB] p2: 101.4° selective Gaussian pulse [20 ms, 59.5 – 1.04 = 58.46 dB] p3: 69.3° selective Gaussian pulse [20 ms, 59.5 + 2.27 = 61.77 dB] p4: 161.0° selective Gaussian pulse [20 ms, 59.5 – 5.05 = 54.45 dB] p5, p6, p7, p8: 90° ¹H transmitter pulse [9 μs, 0 dB] dl:2s d2: 2 ms d3: 10 ms g1–g4: sinusoidal-shaped field gradients, 2 ms duration, with gradient loop counters, lock blanking and gradient coil blanking switches according to the actual instrumentation used. Gradient strength ratio: 80 : 40 : 20: 10. ds: 8

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 a DRX-400 spectrometer with a 5 mm inverse multinuclear gradient probe-head. Compare the result with those in Exps. 11.17 to

7. Comments

The basic idea of this solvent suppression method is first to excite only the solvent signal by a selective pulse and to dephase this transverse magnetization using a pulsed field gradient. A subsequent hard r.f. pulse will then excite only the resonances of the