BRAINCAKEPrecise Molecular Mass
The precise molecular mass of a compound is found from the m/z value of its molecular ion, M+ (the whole molecule that has lost one electron), in a high resolution mass spectrum. The mass of the lost electron is negligible, so this m/z equals the precise Mr.
To use it, you calculate the precise mass of each possible molecular formula by adding the relative isotopic masses of its atoms, then pick the formula that matches the measured value:
1H = 1.0078 12C = 12.0000 14N = 14.0031 16O = 15.9949
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Key terms in this lesson
- relative isotopic mass
- The mass of an atom of a specific isotope relative to one-twelfth of the mass of an atom of carbon-12.
More in Modern Analytical Techniques
- High Resolution Mass Spectrometry
- Chromatography
- Thin-Layer Chromatography
- High Performance Liquid Chromatography
- Gas Chromatography
- Retention Times
- Nuclear Magnetic Resonance
- Chemical Shift
All 15 lessons in Modern Analytical Techniques · All Edexcel A-level Chemistry topics