NMR spectroscopy

What is NMR analysis used for?

Nuclear magnetic resonance spectroscopy is an efficient tool in organic chemistry and quality control of different industries, as it can provide detailed information about the composition of a sample. NMR provides information about the functional groups of molecules and different isotopes of atoms. In addition, intermolecular interactions, such as small protein-ligand interactions, biomolecular dynamics, and low-transient and low-affinity complexes can be studied with NMR.

The result of, for example, a 1H NMR analysis is a spectrum with several signals corresponding to the number of chemically different types of hydrogen nuclei in the molecule. The position of these signals represents the chemical shifts, revealing what kind of chemical environment each of the nuclei is in. The relative areas under these signals (obtained by integration) tell how many hydrogen atoms of each type there are in the molecule. Lastly, the splitting pattern reveals the number of neighboring hydrogens for each individual hydrogen atom. Based on this information, a high-resolution structure of the molecule can be created.

NMR spectroscopy can be used to analyze both known and unknown compounds. Previously unknown components can be identified through comparison with established libraries of NMR spectra.

How does NMR spectroscopy work?

The principle of NMR is based on the ability of spinning nuclei to resonate with a certain magnetic field as a result of the magnetic properties of the atom's core and core electrons to survey the chemical environment of the atom. The nuclei of some atoms spin while others do not. The spinning nuclei include, for example, 1H and 13C, which can be utilized in 1H NMR and 13C NMR analyses, respectively. Other spinning nuclei can also be used, but hydrogen and carbon are the most common because of their presence in most organic compounds.

In general, all moving charged particles generate a magnetic field. When a sample containing spinning nuclei of interest is placed between the two poles of a powerful magnet in the NMR spectroscope, a strong magnetic field goes through the sample. The magnetic field causes a perturbation in the atoms, which leads to a change in the spins of their electrons.

This change in the spin is called electron relaxation, and it is unique for every element. As a result, the spinning nuclei of the atoms are charged electrically and they start to behave like magnets. Therefore, the nuclei align with or against the applied magnetic field creating an energy difference. Then, a fixed radio frequency is used to change the magnetic field to even out the energy differences. When the energies match, the nuclei can change spin states meaning they can resonate and give off a magnetic signal detected by the NMR machine. Based on the characteristic electron relaxations of elements, the structure of the molecules in the sample can be determined.

Suitable samples and sample preparation

NMR can be performed on both solid and liquid samples. Extensive sample preparation is usually not necessary: samples are just diluted to a suitable NMR solvent before analysis. Paramagnetic sample materials (ones with unpaired electrons) and large molecule sizes may cause the spectral lines to broaden to a point where the results are rendered unusable. For paramagnetic samples, EPR spectroscopy may be a more suitable method, while cryo-EM can be used to characterize large molecules.

Need an analysis?

Measurlabs offers 1H, 13C, and various 2D NMR experiments at competitive prices and fast turnaround times. You can contact our experts through the form below or at info@measurlabs.com to discuss the testing options and request a quote for your sample material.