Method for NMR spectroscopy with sustained induction decays of long-lived coherences
A method for nuclear magnetic resonance (NMR) spectroscopy of a sample involves excitation of long lived coherences (LLC) between the singlet state S 0 and the central triplet state T 0 of nuclei of the sample by initiating irradiation of the sample with an rf-field with carrier frequency ω rf ; sustaining of the LLC by maintaining the rf-irradiation during an interval τ 2 ; converting the LLC temporarily into observable magnetization by interrupting the rf-irradiation during an observation interval τ 3 ; detecting NMR-signals during the observation interval τ 3 and reconversion of the observable magnetization back into LLC after the observation interval τ 3 . These steps are repeated n times, wherein n is a positive integer. The method allows ultra high-resolution spectra of long-lived coherences to be obtained.
1. A method for nuclear magnetic resonance (NMR) spectroscopy of a sample, the method comprising the steps of:
a) exciting long lived coherences (LLC) between a singlet state S 0 and a central triplet state T 0 of nuclei of the sample by irradiating the sample with an rf-field having a carrier frequency ω rf ;
b) sustaining the LLC by maintaining rf-irradiation during an interval τ 2 ;
c) temporarily converting the LLC into observable magnetisation by interrupting the rf-irradiation during an observation interval τ 3 ;
d) detecting NMR-signals during the observation interval τ 3 ;
e) reconverting the observable magnetisation back into LLC after the observation interval τ 3 ; and
f) repeating steps (b) to (e) n times, wherein n is a positive integer.
2. The method of claim 1 , comprising exciting the LLC by transforming an initial spin polarization, (I z +S z ) into single quantum coherences (I x −S x ) or (I y −S y ) or (2I y S x −2I z S y ) or (2I x S z −2IS x ) prior to initiating irradiation of the sample with the rf-field.
3. The method of claim 2 , wherein the initial spin polarization is a thermal equilibrium Boltzmann distribution.
4. The method of claim 1 , comprising hyperpolarizing the sample to enhance a spin polarization (I z +S z ), thereby enhancing LLC that are subsequently excited by transforming the enhanced spin polarization (I z +S z ) into enhanced single quantum coherences (I x −S x ) or (I y −S y ) or (2I y S z −2I z S y ) or (2I x S z −2I z S x ) prior to initiating irradiation of the sample with the rf-field.
5. The method of claim 4 , comprising hyperpolarizing the sample using dynamic nuclear polarization.
6. The method of claim 1 , wherein the carrier frequency is ω rf =(Ω I −Ω S )/2, wherein Ω I is a chemical shift of nuclei of the sample with spin I, and wherein Ω S is a chemical shift of nuclei of the sample with spin S.
7. The method of claim 1 , wherein the rf-field is a continuous-wave rf-field.
8. The method of claim 1 , wherein the rf-field is modulated in amplitude.
9. The method of claim 1 , wherein the rf-field is modulated in phase.
10. The method of claim 6 , wherein an amplitude of the rf-field is larger than an offset |Ω I −Ω S |/2.
11. The method of claim 1 , comprising applying a refocusing pulse in a middle of the observation interval τ 3 .
12. The method of claim 1 , comprising carrying out an NMR spectroscopy measurement in a single experiment.