— coherence pathway for N-type signals
– – – coherence pathway for P-type signals
······ coherence pathway for signals leading to sensitivity enhancement

4. Acquisition

Time requirement: 20 min

Sample: 3% strychnine in CDCl₃.

Record normal ¹H and ¹³C NMR spectra of the sample and optimize the spectral widths for CH_n signals. Change to the 2D mode of the spectrometer and load the phase-sensitive gs-HSQC pulse program with echo/anti-echo acquisition and sensitivity enhancement. You have to set:

td2	1 k data points in F₂
td1	2 times 64 data points in F₁
sw2	10 ppm
sw1	165 ppm
offset of ¹H frequency	middle of ¹H NMR spectrum
offset of ¹³C frequency	middle of ¹³C NMR spectrum
p1, p4, p6, p8, p10	90° ¹H transmitter pulse
p2, p5, p7, p9, p11	180° ¹H transmitter pulse
p13, p15, p17	90° ¹³C decoupler pulse
p12, p14, p16, p18	180° ¹³C decoupler pulse
p3	2 ms ¹H trim pulse
d1	2 s
d2	1/[4J(C,H)] = 1.8 ms, calculated from ¹J(C,H) ≈ 140 Hz
d3	same duration as gradient pulse, 1.6 ms used
initial value for t₁ evolution	3 μs
increment for t₁ evolution	1/[2·sw1]
¹³C decoupler attenuation and 90° pulse for GARP	19 dB, 70 μs
g1, g2	sinusoidal-shaped field gradients with 5% truncation, 1.6 ms duration and ca. 0.1 T/m strength, with gradient loop counters, ring-down delays (100 μs), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio: 4 : 1 : −4 : 1
ds	8
ns	1

For the phase-sensitive echo/anti-echo scheme in F₁ use simultaneous data mode in F₂. The pulse sequence uses one scan within the go loop. The echoes (gradients: +4, +1) and the anti-echoes (gradients: −4, +1) are stored in different blocks and are sampled with the 180° phase shift of p17. Two further loops cycle the acquisition phase and the phases of p15 and p4. Thus, the experiment shown was performed with 4 scans of 64 echo accumulations and with 4 scans of 64 anti-echo accumulations.