NMR (Nuclear Magnetic Resonance) Testing

Scope

NMR testing covers the structural identification, compositional analysis, and purity assessment of organic and many inorganic substances through the measurement of nuclear magnetic resonance signals. The nucleus observed, the field strength, and the experiment type are selected to suit the analytical question.

Key aspects of the technique include:

• Common nuclei observed – ¹H (proton) and ¹³C are the most widely used; ¹⁹F, ³¹P, ¹⁵N, and others are observed for specific applications
• Chemical shift – the resonance frequency of each nucleus shifts with its local electronic environment, revealing functional groups and connectivity
• One-dimensional experiments – ¹H and ¹³C spectra giving the fundamental structural information
• Two-dimensional and advanced experiments – correlation experiments (e.g., COSY, HSQC, HMBC) that map how nuclei are connected to each other, used to elucidate complex or unknown structures
• Sample form – most commonly solution-state, with the sample dissolved in a deuterated solvent in a thin glass NMR tube; solid-state NMR is available for insoluble materials
• Information obtained – molecular structure, functional groups, isomer and conformational information, relative purity, and the composition of mixtures

Applications

• Structure elucidation – determining the structure of unknown compounds and confirming the structure of synthesized molecules, a core use in chemistry and pharmaceutical development
• Polymer characterization – determining polymer composition, tacticity, end groups, copolymer ratios, and branching
• Chemical identification and verification – confirming the identity and purity of chemicals, reagents, and raw materials
• Mixture analysis – identifying and quantifying components in mixtures by matching signals against known spectra
• Metabolomics and natural products – characterizing complex biological and natural-product samples
• Quality control – confirming batch-to-batch consistency of composition and structure for chemical and polymer products

Benefits

• Provides detailed structural information from a single measurement – NMR reveals connectivity, functional groups, and molecular arrangement at a level of detail few other single techniques can match
• Non-destructive – the sample is not consumed or altered, so it can be recovered and used for further testing after analysis
• Quantitative – signal intensity is proportional to the number of nuclei, so NMR can quantify components and assess relative purity directly, without compound-specific calibration in many cases
• Works on known and unknown compounds – NMR both confirms expected structures and helps identify unknowns, including by matching against spectral libraries
• Versatile across sample types – solution- and solid-state methods, and the choice of observed nucleus, let the technique address a wide range of organic, polymeric, and inorganic materials