(a) Effect of a slight perturbation (5%) by a single scan on the steady-state ¹H polarization as a function of the recycle time T_rec, calculated from eqn (1.7) for T₁ time constants varying from 400 ms to 3.4 s. (b) Off-resonance performance of two commonly used refocusing (180°) pulse shapes, REBURP (black curves) and Q3 (red curve). The steady-state water ¹H polarization has been measured after applying the shaped pulse (nominal band width of 4 ppm) 32-times with an inter-pulse delay of 100 ms. The off-resonance profile is obtained by repeating the measurement for different shaped pulse offsets with respect to the water frequency. Straight lines correspond to measurements on a last generation cryoprobe, while the black dashed line shows the result obtained on an old cryoprobe. (c) Intensity ratios measured for individual amide ¹H sites in ubiquitin (pH 7.4, 20 °C) in ¹H–¹⁵N BEST-TROSY spectra measured on samples with and without a paramagnetic water relaxation compound (0.5 mM gadodiamide).