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NMR examines the behaviour of certain atomic nuclei in a strong magnetic field. 1H and 13C NMR are widely used to study the chemical environments of hydrogen and carbon atoms.
This topic is closely related to What is FTIR spectroscopy? and Which analytical method is used for chemical identification?, which provide additional context for the interpretation and characterization of chemical materials.
Signals appear at chemical shifts determined by the electronic environment around a nucleus. This helps distinguish functional groups and positions within a molecule.
In 1H NMR, integration can indicate relative numbers of protons. Splitting patterns and coupling constants provide additional information about neighbouring nuclei.
NMR can strongly support the identity of an organic compound and can reveal some impurities. Not every impurity is equally sensitive to detection or straightforward to quantify.
NMR is especially valuable for structural confirmation. Chemical shift, integration and coupling together form a detailed structural fingerprint.
Electrons shield atomic nuclei from the applied magnetic field. Differences in electronic environment therefore shift resonances to different positions. These chemical shifts are reported in ppm so spectra obtained at different instrument field strengths can be compared.
Proton NMR is sensitive and often gives information about proton environments, relative counts and neighbouring atoms. Carbon-13 NMR provides a complementary view of carbon environments. The two experiments answer related but different structural questions.
A proton signal can split through spin-spin coupling with nearby nuclei. Doublets, triplets, multiplets and coupling constants can therefore reveal relationships between atoms. Real spectra may be more complex than simple textbook splitting rules.
NMR samples are normally measured in deuterated solvents. Residual solvent, water and reference signals can appear in the spectrum and should not automatically be mistaken for sample impurities. The chosen solvent can also influence chemical shifts.
NMR can reveal unexpected signals and quantitative NMR can determine content when performed with an appropriate internal or external standard and suitable acquisition parameters. A routine identity spectrum, however, should not automatically be interpreted as a validated purity assay.
NMR is particularly strong for connectivity and structural environment, whereas MS is strong for mass information and chromatography for separation. When these independent observations agree with the proposed structure, the combined identity evidence becomes considerably stronger.
Analytical data cannot be separated completely from the conditions under which they were produced. Instrument settings, sample preparation, reference materials, calibration and data processing can all influence the final result. Two values that look identical at first glance may therefore not carry exactly the same analytical meaning. When documents are compared, the method and the definition of the reported value matter just as much as the final number.
A reliable reference material can help compare analytical observations with a known substance. Its value depends on the question being asked: retention behaviour, a spectrum or another characteristic can provide strong support under controlled conditions. Reference comparison does not replace critical review of the complete dataset. The identity of the reference, the method used and the similarity of measurement conditions determine how strong the comparison really is.
A technically convincing result consists of more than a percentage or one prominent signal. Clear sample identification, interpretable raw or derived data, logical specifications and a suitable analytical method make a result easier to assess. Internal consistency also matters: chemical name, formula, molar mass, batch information and analytical conclusion should not contradict one another. Where different elements do not align, further verification is preferable to treating one favourable value as decisive.
Information has different functions in an SDS, Technical Data Sheet and Certificate of Analysis. An SDS primarily addresses safety and hazard information, a TDS describes technical characteristics, and a CoA generally reports results for a specific batch. Analytical information has the right meaning only when it is clear which document contains it, which material or batch it concerns, and whether it is a specification, typical value or actual measured result.