What is nmr in technology

The NMR spectroscopy is an important physical-analytical method for identification of organic substances and for Structure elucidation unknown chemical compounds. This is made clear not least by the fact that this procedure is explicitly described both in the European Pharmacopoeia (Ph.Eur.) And in the United States Pharmacopeia (USP). Nevertheless, the method is only used in the individual monographs in exceptional cases, which can be explained, among other things, by the fact that an NMR measurement in public pharmacies is generally not feasible.

Basics of the method

The NMR spectroscopy (nuclear magnetic resonance spectroscopy) is based on the fact that certain atomic nuclei, namely those that contain an odd number of protons and / or neutrons, have a nuclear spin and thus a magnetic moment. The most important nuclei active in NMR are 1H, 13C, 19F and 31P. Many other nuclei, e.g. 23Na and 29Si, can also be measured by NMR spectroscopy.

The nuclear spin of a proton is 1/2. In an externally applied magnetic field, it adopts one of two orientations, namely either parallel or antiparallel to the field lines of the magnet. Accordingly, the proton is at a lower or higher energy level. There are two different energy states between which a transition is possible when the sample is irradiated with radio waves.

The recording of NMR spectra takes place with the help of a nuclear magnetic resonance spectrometer, which, to put it simply, consists of the following Components consists:

  • Magnet to generate a constant, homogeneous magnetic field
  • Sample holder with temperature control
  • Radio frequency transmitter
  • Radio frequency receiver

The NMR spectrum provides a large amount of important information, whereby the following parameters are used for the evaluation:

  • Position of the signal
  • Number of resonance signals
  • Chemical shift
  • Intensity of the resonance signals (integration curve)
  • Spin-spin coupling
  • Coupling constant

NMR spectroscopy in the European Pharmacopoeia

The pharmacopoeia describes the method on the one hand in the section on methods of physics and physical chemistry in Chapter 2.2.33 (nuclear magnetic resonance spectroscopy). This text goes into detail about the possible uses and the practical implementation of the method. The Content determination by means of NMR spectroscopy (qNMR) was explicitly included years ago and the corresponding framework conditions were defined. On the other hand, NMR technology is also used in Chapter 2.2.64 (peptide identification by nuclear magnetic resonance spectroscopy) described.

As Examples For drug monographs in which an NMR spectroscopic method is specifically used, the following are to be named:

  • Heparin sodium
  • Lauromacrogol 400
  • Poloxamers

NMR spectroscopy in the USP

In the USP, NMR spectroscopy is described in the following chapters:

  • General Chapter <761> Nuclear Magnetic Resonance Spectroscopy
  • General Information Chapter <1761> Applications of Nuclear Magnetic Resonance Spectroscopy
  • General Information Chapter <1238> Vaccines for Human Use - Bacterial Vaccines

Examples for drugs that are examined by USP NMR spectroscopy are:

  • Orphenadrine Citrate
  • Goserelin Acetate
  • Poloxamer