Method for nuclear magnetic resonance (NMR) spectroscopy measurements using long-lived coherences (LLC)
A method for nuclear magnetic resonance (NMR) spectroscopy of a sample comprises preparation of the sample and carrying out an NMR spectroscopy measurement. Preparation includes excitation of long lived coherences (LLC) between the singlet state S 0 and the central triplet state T 0 of nuclei of the sample. The thermal equilibrium Boltzmann distribution (I z +S z ) is thereby transformed into a difference (I z −S z ), which is flipped to the transverse plane, and irradiation of the sample with an rf-field is initiated. The LLC is sustained by maintaining the rf-irradiation during an interval t 1 and the LLC is converted into observable magnetisation by interrupting the rf-irradiation. The method allows nuclear magnetic resonance spectroscopy measurements with improved spectral resolution.
1. A method for nuclear magnetic resonance (NMR) spectroscopy of a sample with which the sample is prepared and an NMR spectroscopy measurement is carried out, the method comprising the steps of:
a) transforming a thermal equilibrium Boltzmann distribution (I z +S z ) into a difference (I z −S z );
b) flipping the difference (I z −S z ) to a transverse plane;
c) irradiating the sample with an rf-field to effect, in combination with steps a) and b), excitation of long lived coherences (LLC) between a singlet state S 0 and a central triplet state T 0 of nuclei of the sample;
d) sustaining the LLC by maintaining rf-irradiation during an interval t 1 ; and
e) converting the LLC into observable magnetisation by interrupting the rf-irradiation.
2. The method of claim 1 , wherein the rf-field is a continuous wave rf-field.
3. The method of claim 1 , wherein, in step a), the thermal equilibrium Boltzmann distribution (I z +S z ) is transformed into a difference (I z −S z ) by applying a semi-selective π pulse.
4. The method of claim 1 , wherein, in step b), a (π/2) pulse is applied.
5. The method of claim 3 , wherein, in step b), a (π/2) pulse is applied.
6. The method of claim 5 , wherein, in step a) at least two semi-selective π pulses are applied either simultaneously or consecutively in order to excite (I z −S z ) of different kinds of nuclei of the sample, and, in step b), a single (π/2) pulse is applied.
7. The method of claim 1 , wherein the NMR spectroscopy measurement is a 2D NMR spectroscopy measurement.
8. The method of claim 1 , wherein the NMR spectroscopy measurement is a liquid-state NMR measurement.
9. The method of claim 8 , wherein the NMR measurement is carried out in isotropic solution.