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 through the identification of components and their quantities. NMR provides information about the functional groups and their relative position to each other of molecules and different isotopes of atoms. Intermolecular interactions, such as small protein-ligand interactions, biomolecular dynamics, and low-transient and low-affinity complexes, can also be studied.

NMR can be used to analyze both known and unknown compounds. To identify compounds, existing spectral libraries can be utilized for data interpretation. Manual spectral interpretation can also be done in combination with other analysis techniques, such as mass spectroscopy, to find the exact structure of the compound.

How does NMR spectroscopy work?

The principle of NMR is based on the ability of NMR active 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 active nuclei have two or more spin states that allow the energy to change in the nuclei. Active nuclei include, for example, 1H and 13C, which can be utilized in 1H NMR and 13C NMR analyses, respectively. Other NMR active nuclei, such as 15N, 31P, 19F, and 29Si, 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 active 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.

As a result, the 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 instrument. Based on the characteristic electron relaxations of elements, the structure of the molecules in the sample can be determined.

Interpreting NMR spectra

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 hydrogen atoms for each individual hydrogen atom. Based on this information, a high-resolution structure of the molecule can be created.

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 for a wide range of sample matrices. Please contact our experts through the form below to discuss the testing options and request a quote for your sample.