4. Acquisition

Time requirement: 1h Sample: D₂O with 10% Methanol, 5% n-Butanol and 5% Triethylene-glycol.

Record a normal 1D ¹H NMR spectrum and optimize the spectral width. Set and control the temperature to 300 K. Use a high air-flow to avoid convections in the sample. [Other authors recommend no air-flow at all]. Switch to the 2D mode of the spectrometer software, and load the DOSY pulse program. First record a minimal ¹H NMR DOSY spectrum (ns = 1) with a gradient ramp of 8 gradient strengths in order to observe complete signal decay for a given diffusion delay and gradient power, and readjust the gradients accordingly. You have to set:

td2: 4 k data points in F, td1: 64 data points in F; (gradient ramp) sw2: 4.7 ppm o1: middle of selected ¹H NMR region p1, p3, p4, p6, p7: 90° ¹H transmitter pulse p2, p5: 180° ¹H transmitter pulse d1:5s d2: diffusion delay 50 ms d3: eddy current delay 5 ms g1, g2, g4, g5 sinusoidal-shaped bipolar field gradients (gradient strength ratio: 1: -1:1:-1), 3 ms duration; ring-down delays [50 μs], lock blanking and gradient coil blanking switches according to actual instrumentation used. The strength of the gradients has to be varied during this experiment, so you have to define a gradient ramp containing 64 values ranging between 2 and 95% of the total gradient strength provided by the gradient amplifier; details are very dependent on the software used.

g3 and gé6 are spoil gradients of 1 ms duration; a g3 : g6 ratio of 7 : 13 was

5. Processing

Apply zero-filling to 128 real data points in F, and use an exponential window with lb = | Hz line-broadening in F2. Transform only in the F, direction. Each signal will now display a decay curve in F; as the gradient strength increases. The extraction of decay constants and their transformation into a 2D plot requires special mathematics, the handling of which is very dependent on the software version provided by the instrument manufacturer.

The figure shows the DOSY spectrum obtained on a DRX-400 spectrometer. As can be seen, the signals of the four different compounds are roughly ordered in F; by the