NMR- spectroscopy is a type of spectroscopy by which we can determine the quality and purity of a sample and molecular structure of a compound.
What is NMR?
NMR is an abbreviation of Nuclear Magnetic Resonance. So, NMR-spectroscopy is a spectroscopy technique based on nuclear magnetic resonance of atoms of the sample being examined.
It is based on the fact that nuclei of most of the atoms shows spin and all nuclei are electrically charged. NMR-spectroscopy is based on the absorption of electromagnetic radiation in the radio frequency region 3kHz-300 GHz. Nuclei of atoms has spin and electrical charge, so they generate magnetic field. In presence of external magnetic field, nuclei of atoms align themselves either in the direction of external magnetic field or in the opposite direction of the external magnetic field.
In the presence of external magnetic field, energy transfer takes place between ground state to excited state.
It takes place at a wavelength that matches with radio frequencies and when the electron returns from excited state to ground state, it emits the radio wave of same frequency. This emitted radio frequency gives NMR-spectrum. This emitted radio frequency is proportional to the strength of the applied external magnetic field.
B0= external magnetic field
γ= the between the nuclear magnetic moment and angular moment.
Sample holder used in NMR-spectroscopy is a glass tube. Generally, 8cm long.
Permanent powerful magnet is used to provide homogenous magnetic field.
Magnetic coils also generate magnetic field.
Sweep generators can modify the strength of the magnetic field.
Radio frequency input oscillator produces powerful but short radio waves.
Radio frequency output receiver is used to receive radio frequency signal coming from the sample.
System is connected with a computer to analyze and record NMR-spectrum.
Generally, carbon tetrachloride and carbon disulphide are used as solvents for samples being examined in NMR-spectroscopy.
Applications of NMR-Spectroscopy –
NMR-applications are as follows-
1. It is used for quantitative analysis of mixtures of compounds.
2. It is used for quality control.
3. It is used to determine the molecular structure of compounds.
4. It is used to check the purity of samples.
5. It is used in food science.
6. It is used in the study of drugs.
7. It is used in the study of biofluids, cells and nucleic acids.