BRAINCAKEHigh Resolution Mass Spectrometry
An ordinary (low resolution) mass spectrometer gives m/z values to the nearest whole number. A high resolution mass spectrometer measures m/z values very precisely, to four or more decimal places.
This matters because relative isotopic masses are not exact whole numbers. By definition, carbon-12 has a relative isotopic mass of exactly 12 (12.0000). Every other isotope differs slightly from a whole number, because of the way mass changes when nucleons bind together:
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.
- molecular ion peak
- The peak in a mass spectrum, usually at the highest m/z, produced by the molecular ion formed when a molecule loses one electron.
More in Modern Analytical Techniques
- Precise Molecular Mass
- 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