The IICT schemes are composite pulse sequences specifically designed for isotropic mixing purpose in TOCSY experiments (see The TOCSY block).

Easy implementation on AVANCE spectrometers.

Several versions of the IICT scheme have been proposed ( 93JMRA298-105 ):

IICT-1: R(0)R(0)R(180)R(180)-R(0)R(180)R(180)R(0)
where R=350.9(0)290(180)54.2(0)298.2(180)339.6(0)

IICT-2: R(0)R(0)R(180)R(180)
where R=320.7(0)374.9(180)299.2(0)266.1(180)36.2(0)261.8(180)357.9(0)278.9(180)346(0)

IICT-3: R(0)R(0)R(180)R(180)
where R=38.6(0)302.2(180)335(0)42.2(180)306(0)261.6(180)24.3(0)15.6(180)24.3(0)
261.6(180)306(0)42.2(180)335(0)302.2(180)38.6(0)

IICT-4: R(0)R(0)R(180)R(180)-R(0)R(180)R(180)R(0)
where R=38(0)112.6(60.5)205.9(68.6)256.9(280.1)101.9(5.2)265.5(281.6)242.6(72.6)66.6(66.9)44.9(0)

All these approaches offer excellent global offset quality factors ensuring that coherence transfer is efficiently achieved over the chemical-shift range of interest:
 

Sequence	Qx	Qy	Qz
IICT-1	0.73	0.52	0.57
IICT-2	0.71	0.51	0.5
IICT-3	0.72	0.52	0.52
IICT-4	0.59	0.58	0.63
MLEV-16	-0.31	-0.31	0.16
DIPSI-2	0.68	0.44	0.46
FLOPSY-2	0.62	0.55	0.61

 

Calibration of 90º and 180º pulses must be made at the required power. In general, for TOCSY applications, the power is adjusted to give a 90º pulse about 30-35 microseconds. A 10% variation in such calibrations could be tolerated.

For further experimental details, see the following tutorials:

• Tutorial: 90º ¹H observe pulse calibration.
• Tutorial: 2D TOCSY experiment.