4. Acquisition

Time requirement: 10 min Sample: 3% strychnine in CDCl₃ Record normal ¹H and ¹³C NMR spectra of the sample and optimize the spectral widths for CH, signals. Change to the 2D mode of the spectrometer and load the phase-sensitive E-HSQC pulse program with echo/anti-echo acquisition. To record a 2D spectrum a where CH and CH; groups have different phase from CH? groups you have to set:

td2: 2 k data points in F, tdl: 2 times 128 data points in F; sw2: 9 ppm swl: 140 ppm offset of ¹H frequency: middle of ¹H NMR spectrum offset of ¹³C frequency: middle of ¹³C NMR spectrum p1, p4, p7, p9, p11: 90° ¹H transmitter pulse p2, ps, p8, p10, p12: 180° ¹H transmitter pulse p6: H transmitter editing pulse, set to 180° p14, p16, p18: 90° ¹³C decoupler pulse p13, p15, p17, p19: 180° ¹³C decoupler pulse p3: 2 ms ¹H trim pulse dl:2s d2: 1/[4(C,H)] = 1.78 ms, calculated from 'J(C,H) = 140 Hz d3: editing delay, set d3 = d4 minus effective gradient duration g1 d4: editing delay, set to 1/[2/(C,H)] = 3.57 ms d5: delay for PEP mode (Preservation of Equivalent Pathways or "sensitivity enhancement”) set to 1/[8/(C,H)] = 0.9 ms d6: same duration as gradient pulse, 1.05 ms used initial value for t, evolution: 3 μs increment for f, evolution: 1/[2-sw1] BC decoupler attenuation and 90° pulse for GARP [11 dB, 75 μs] g1, g2: 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 instrumentation used. Gradient strength ratio: 4: 1 :4:-1 ds: 1 For the phase-sensitive echo/anti-echo scheme in F; use simultaneous data mode or digital quadrature detection in F).

To record a spectrum b, where all signals other than the CH groups are suppressed, you have to set differently:

p6: ¹H transmitter editing pulse, set to 90°