Physical Chemistry, Invited Lecture
Spectroscopic separation of 13C NMR spectra of complex isomeric mixtures by the CSSF-TOCSY-INEPT experiment
A. Moreno1, H. Sommer2
1Bruker BioSpin AG, 2Firmenich SA
Among the most critical parameters for NMR experiments are spectrometer stability and sensitivity. The spectrometer hardware for optimal results will depend strongly on the application used. The presentation will cover probe choice and probe design for high resolution NMR applications. The impact of the sensitivity gain by CryoProbes[1] for 13C detection will be illustrated with an example of a complex mixture analysis using the CSSF-TOCSY-INEPT experiment[2].

This experiment uses the resolving power of a chemical shift selective filter (CSSF) to separate strongly overlapped 1H NMR signals in complex mixtures. The selectivity of the CSSF is then amplified via magnetization transfer from the excited proton(s) to all other protons within the same coupling network during TOCSY isotropic mixing. Subsequent refocused INEPT transfer from proton to carbon spins allows then the acquisition of proton-decoupled 13C sub-spectra.
Figure: Spectroscopic separation of a 1:1 mixture of diastereomers 1 and 2 (~360mM each). (A) Selection of 1H chemical shifts for selective excitation. (B) CSSF-TOCSY-INEPT experiments with 1H selective excitation of a–f generate six 13C NMR sub-spectra.

[1] H. Kovacs, D. Moskau, Encyclopedia Biophys. 2013, 1, 392–396.
[2] L. Yang, A. Moreno, W. Fieber, R. Brauchli, H. Sommer, Magn. Reson. Chem. 2015, 53, 304–308.