4. Acquisition

Time requirement: 1.5 h

Sample: 3% strychnine in CDCl₃.

Record normal ¹H and ¹³C NMR spectra of the sample, optimize the spectral widths and determine the offsets. Change to the 2D mode of the spectrometer and load the gs-HETLOC pulse program. You have to set:

td2	4 k data points in F₂ for sufficient resolution
td1	256 data points in F₁
sw2	10 ppm
sw1	10 ppm
offset of ¹H frequency	middle of ¹H NMR spectrum
offset of ¹³C frequency	middle of ¹³C NMR spectrum
p1, p3, p4, p6, p8	90° ¹H transmitter pulse [9 μs, 0 dB]
p2, p5, p7, p9, p13	180° ¹H transmitter pulse [18 μs, 0 dB]
p10, p12	¹H 90° transmitter pulse at spin-lock power level [40 μs, 22 dB]
p11	DIPSI-2 spin-lock sequence, total duration 70 ms
p15, p17	90° ¹³C decoupler pulse [13 μs, −6 dB]
p14, p16, p18, p19, p20, p21 (optional)	180° ¹³C decoupler pulse [26 μs, −6 dB]
d1	relaxation delay 2 s
d2	1/[4J(C,H)] = 1.72 ms, calculated from ¹J(C,H) ≈ 145 Hz
d3	1/[2J(C,H)] = 3.44 ms, calculated from ¹J(C,H) ≈ 145 Hz
d4	3 times effective gradient duration = 3.15 ms
d5	effective gradient duration = 1.05 ms
start increment for t₁ evolution	3 μs
increment for t₁ evolution	1/[2·sw1]
g1–g5	sinusoidal-shaped field gradients, 1 ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (50 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used, sign of g5 varied according to echo/anti-echo mode

Relative gradient strengths	g1	g2	g3	g4	g5
	−20	−25	25	11	11

ns	8
ds	2 × ns

5. Processing

Apply zero-filling in F₁ to 512 and in F₂ to 4 k words in order to have a matrix of 4k × 512 real data points. Before Fourier transformation use an exponential window in F₂ with lb = 0.5 Hz and a π/2-shifted squared sine window in F₁. Use the echo/anti-echo scheme for the calculation of the spectrum. Phase correction may be necessary in both dimensions.