CRAPT: an improved version of APT with compensation for variations in JCH.

A modified version of the attached proton test (APT) sequence for (13)C spectral editing, which we call CRisis-APT (CRAPT), is developed and tested on representative organic compounds. CRAPT incorporates (13)C compensation for refocusing inefficiency with synchronized inversion sweeps (CRISIS) pulses in combination with (1)H broadband inversion pulses to give improved compensation for variations in (1)JCH along with improved refocusing efficiency. It is shown that CRAPT gives edited (13)C spectra with only small losses in sensitivity (between 8% and 15% for strychnine, 1, menthol, 2, cholecalciferol, 3, and isotachysterol, 4), compared with basic (13)C spectra obtained on the same compounds. CRAPT also gives significantly better signal/noise than DEPTQ for nonprotonated carbons. Therefore, we conclude that CRAPT is an improvement over APT or DEPTQ or a combination of DEPT135 with a full (13)C spectrum for routine (13)C spectral editing of organic compounds.