Use of NMR in Impurity Profiling for Pharmaceutical Products

Introduction:

Nuclear Magnetic Resonance Spectrometry (NMR) is the best instrument technique in the pharmaceutical for the identification and characterization of impurities.

NMR is also called as proton NMR since it gives structural clarification based on the number of proton pair present in the structure. The key use of NMR spectroscopy is that it gives identification and molecular structure elucidation of compound of interest. It also offers indication about exact bonding of molecule in the structural evidence, configuration, atomic integration and their stereochemistry. Hydrogen is the very easy, reactive, and most regularly detected nucleus.

Principle: The principle based on nuclei have spins and all atomic nuclei are electrostatic charged. The interaction spin of nuclei with magnetic field subsequently absorption of radio frequency. Magnetic measurement depends upon the spin of unpaired electron whereas NMR measures magnetic moment caused by the spin of protons and neutrons.

Uses of NMR:

NMR spectroscopy has numerous uses in pharmaceutical. Method development and sample preparation is very easy also it’s non-destructive nature technique. NMR spectroscopy is rugged and quasi-universal detector which is sensitive to low molecular weight organic compounds.

NMR spectroscopy sensitivity improved by following advancement in the technology:

1. Increase in sample concentration and processing with higher sample quantity,
2. Excessive magnetic field power i.e. shielded and progressively sturdier high-field magnets,
3. Latest sensors such as cryogenic probes,
4. Improved sensitivity to nanomolar range,
5. Solvent suppression techniques,
6. Small volume or micro tubes and micro coil capillary assembly,
7. Use of NMR crystallography
8. Use of fluorine NMR and Nitrogen NMR spectroscopy,
9. Nanoparticle (Monolayer-protected gold nanoparticles) assisted NMR spectroscopy,
10. Maximum number of scans with advance data processing,
11. Methyl TROSY-spectroscopy, useful for higher molecular weight complexes and complicated biological structures.

The utmost advantageous trials for spectral assignment are COSY and TOCSY (homo nuclear correlation), NOESY and ROESY (nuclear Over Hauser effect), HSQC, HMBC and HMQC (hetero nuclear single or multiple quantum coherence spectroscopy).

The main applications of NMR are structural clarification of small organic molecules. Quantitative HNMR spectroscopy is very much useful in purity calculation of small organic molecules also enhancing the identification of potential impurities. It is also powerful tools for the identification and elucidation of chiral compound and for the discrimination of diastereomers.

Conclusion:

NMR spectroscopy is found to be most popular technique for the identification of unknown impurities in pharmaceutical products. NMR spectroscopy is generally used to acquired structural information. NMR is very useful technique to get the evidence about the structure of the compound in a combination of impurity. Main application of NMR is quantitative determination of the low level of impurities.

References:

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8. Malz, F. Quantitative NMR in the solution state NMR. In NMR Spectroscopy in Pharmaceutical Analysis; Holzgrabe, U., Wawer, I., Diehl,
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