Spectroscopy is a technique in which we study the interaction between matter and electromagnetic radiation. There are different types of spectroscopy such as infrared spectroscopy, UV-spectroscopy, NMR-spectroscopy, etc. In this article, we will discuss NMR- spectroscopy. In NMR-spectroscopy, we will cover the following- NMR-meaning, NMR-spectroscopy principle (or NMR-principle), NMR-instrumentation (or NMR-spectroscopy instrumentation), and application of NMR-spectroscopy.
What is NMR-Spectroscopy?
NMR- spectroscopy is a type of spectroscopy by which we can determine the quality and purity of a sample and the 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 the nuclear magnetic resonance of atoms of the sample being examined.
NMR-Spectroscopy Principle
It is based on the fact that the nuclei of most of the atoms show spin and all nuclei are electrically charged. NMR-spectroscopy is based on the absorption of electromagnetic radiation in the radiofrequency region 3kHz-300 GHz. Nuclei of atoms have spin and electrical charge, so they generate magnetic fields. In the presence of an external magnetic field, nuclei of atoms align themselves either in the direction of the external magnetic field or in the opposite direction of the external magnetic field.
In the presence of an external magnetic field, energy transfer takes place between the ground state to the excited state.
It takes place at a wavelength that matches with radio frequencies and when the electron returns from an excited state to ground state, it emits the radio wave of the same frequency. This emitted radio frequency gives NMR spectrum. This emitted radiofrequency 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.
NMR-Instrumentation –
Sample holder used in NMR-spectroscopy is a glass tube. Generally, 8cm long.
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Permanent powerful magnet is used to provide a homogeneous magnetic field.
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Magnetic coils also generate magnetic fields.
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Sweep generators can modify the strength of the magnetic field.
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Radio frequency input oscillator produces powerful but short radio waves.
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Radio frequency output receiver is used to receive radio frequency signals coming from the sample.
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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-
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It is used for quantitative analysis of mixtures of compounds.
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It is used for quality control.
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It is used to determine the molecular structure of compounds.
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It is used to check the purity of samples.
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It is used in food science.
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It is used in the study of drugs.
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It is used in the study of biofluids, cells and nucleic acids.
Limitations of the NMR Spectroscopy and Ways to Overcome
NMR spectroscopy is one of the definitive methods used in organic chemistry. However, there are certain limitations to this technique that can come in your way while experimenting. Below you will find the limitations of NMR spectroscopy and what you can do to overcome them.
1. Sensitivity
Even though NMR spectroscopy is a versatile technique, it often fails due to its low sensitivity. It is a huge disadvantage while examining metabolomics or other complex reactions.
There are several methods to overcome the sensitivity problem in NMR spectroscopy. For example, you can use advanced hardware to improve the sensitivity during NMR experiments.
2. Magnetic Field Drift
Drift in the magnetic field has a huge impact on NMR spectroscopy, leading to distorted lineshapes and spectral leaks. This can make the interpretations of the results a lot tougher.
In such cases, you can make certain corrections in the magnetic field while recording the measurement. For this, deuterium present in NMR solvents is detected, which enables the tracking of the magnetic field drift. Subsequently, adjustments in the main field are made with the use of electromagnets at room temperatures.
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