Nuclear Magnetic Resonance Spectroscopy
(NMR)

Bruker Ascend 400 Nuclear Magnetic Resonance Spectrometer

The Bruker Ascend™ 400 MHz Nuclear Magnetic Resonance Spectrometer is a compact NMR spectrometer that uses the Bruker UltraShield™ Plus magnets that offer superior performance, convenience and operational cost savings. The magnet design is based on advanced superconductor technology which allows the utilization of smaller magnet coils that result in a significant size reduction of the system along with reduced magnetic stray fields. The unique jointing technology used in the instrument allows low drift rates leading to outstanding field stability. The External Disturbance Suppression (EDS) technology provides up to around 99% screening efficiency against external magnetic disturbances. The instrument allows the rapid acquisition of routine 1D and 2D NMR experiments. The 1D spectra available from this instrument include 1H and 13C while the 2D correlation options include 1H-1H: COSY, NOSEY, ROSEY, TOCSY, 1H-X: HSQC, HMBC, HMQC and H2BC. Both solid and liquid probes are available for analysis.

Principle

In nuclear magnetic spectroscopy, the local magnetic fields around a sample are observed. The sample to be analysed is placed in a strong magnetic field and is excited by using radio waves. The nuclei exhibit nuclear magnetic resonance which is used to produce the NMR signals. As the intramolecular magnetic field around an atom changes based on the electronic structure of the molecule and its individual functional groups, this information can be used in the characterization of compounds. Given the NMR peaks produced for individual compounds are highly characteristic, NMR has become the definitive method for the identification of the structure of organic compounds. Apart from identification purposes, NMR spectroscopy can be used to obtain detailed information regarding the structure, dynamics, reaction state and chemical environment of molecules. Other than one dimensional spectroscopy, correlational spectroscopy is used to generate 2-dimensional spectra which can be used to determine the structures of molecules that are too complicated to be determined with 1-D NMR spectroscopy.

Strengths

• Minimal sample quantity required
• Proton NMR spectrum can be obtained in a few minutes
• Sample temperature can be varied
• Structural information can be obtained
• Purity of a sample can be analysed

Limitations

• Solubility in a deuterated solvent is necessary. The presence of diamagnetic, paramagnetic or ferromagnetic ions can cause the spectral pattern produced to be broad featureless and uninformative.
• The interpretation of the produced spectra needs to be carried out by a trained scientist.
• Data acquisition times may be long

Applications

• Pharmaceuticals: Identification of drug substances and impurities, identification and characterization of polymorphs
• Natural products: Structure elucidation of natural products, identification of organic impurities present in natural products
• Polymer industry: Chemical structure identification and determination of the purity of polymers 
• Textile industry: Solid state NMR for the analysis of chemical functionalities in textile materials

Technical Specifications

• UltraShieldTM Plus 9.4T magnet
• 5 mm BBFOPLUS probe, optimized for X-nuclei direct observation. Broad band in a frequency range between 31P and 15N. This probe has 2H "lock" channel and z gradient that allows us to carry out 2D spectroscopy and hetero correlation 19F/1H and 1H/19F. The BBFOPLUS probe also includes an automated tuning and matching device (ATM).
• Control temperature unit (from -50 °C to 50 °C)

Experimental Capabilities

• 1D spectra 1H, 13C, 31P, 29Si
• 2D correlation 1H-1H: COSY, NOESY, ROESY, TOCSY
• 2D correlation 1H-X: HSQC, HMBC, HMQC
• Diffusion