4. Acquisition

Time requirement: 5 min

Sample: 1% CHCl₃ in [D₆]acetone.

The instrument must be in the inverse mode, using the proton channel as transmitter and the ¹³C channel as decoupler. First obtain ¹H and ¹³C spectra of the sample and note the offsets of the CHCl₃ signals. You have to set:

td	4 k
sw	500 Hz
o1	on ¹H resonance
o2	on ¹³C resonance
p1	90° ¹H transmitter pulse
p2, p3	90° ¹³C decoupler pulse
d1	5 s
d2	1/[2¹J(C,H)] = 2.33 ms, calculated from ¹J(C,H) = 214 Hz
d3	equal to effective length of gradient pulse and ring-down delay [1.05 ms]
g1, g2	sinusoidal-shaped field gradients of 1 ms duration and ca. 0.01 T/m strength, with gradient loop counter, ring-down delay (50 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient ratio either 4 : −3 or 4 : −5 (dotted line in the coherence pathway diagram)
ds	2
ns	1

5. Processing

Use standard ¹H processing as described in Experiment 3.1.

6. Result

The figure shows the result obtained on a DRX-400 spectrometer with an inverse z-gradient probe-head. Note that the double-quantum filter has suppressed the central line to roughly half of the height of the ¹³C satellites in one single scan.

7. Comments

The double-quantum filter can best be understood with the product operator formalism, and this is detailed in Experiment 6.16. After pulse p2 we have the term

−2 I_Hx I_Cy