4. Acquisition

Time requirement: 75 min

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

Set and control the temperature to 300 K. Use a high air-flow to avoid convections in the sample. 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. Switch to ¹³C observation and load the INEPT-DOSY pulse program. You have to set:

td2: 32k data points in F₂
td1: 32 data points in F₁ (gradient ramp)
sw2: 76 ppm
o1: middle of selected ¹³C NMR region [46 ppm]
p1, p3, p4, p6, p7, p9: 90° ¹H decoupler pulse
p2, p5, p8, p10: 180° ¹H decoupler pulse
p12: 90° ¹³C transmitter pulse
p11, p13: 180° ¹³C transmitter pulse
d1: 2 s
d2: diffusion delay 75 ms
d3: eddy current delay 5 ms
d4: INEPT delay, 1.72 ms, calculated from 1/[4·¹J(C,H)]
g1, g2, g4, g5 sinusoidal-shaped bipolar field gradients (gradient strength ratio: 1 : −1 : 1 : −1), 1.8 ms duration; ring-down delays [50 μs], lock blanking and gradient coil blanking switches according to actual instrumentation used. For the variable gradients used during this experiment you have to define a linear gradient ramp containing 32 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 g6 are spoil gradients of 1 ms duration; a g3 : g6 ratio of −17.1 : −13.2 was used.
ds: 4
ns: 8

5. Processing

No zero-filling will be applied in F₁. Use an exponential window with lb = 10 Hz line-broadening in F₂. Transform only in the F₂ direction, correct the phase and apply a base-line correction. Each signal will now display a decay curve in F₁ as the gradient strength increases. The extraction of decay constants and their transformation into a 2D plot requires special software, which may be very different with different instrument manufacturers.