Accurate Mass
Definition
A mass measured to four or more decimal places, sufficient to compute a unique molecular formula. High-resolution accurate-mass (HRAM) instruments (Q-TOF, Orbitrap, FT-ICR) deliver mass accuracy below 5 ppm, which is the working threshold for formula assignment.
Related terms
- Base Peak
- The most intense peak in a mass spectrum, normalised to 100 percent relative abundance. All other peaks in the spectrum are reported...
- Mass-to-Charge Ratio (M/z)
- The fundamental MS measurement: the mass of an ion divided by its charge number. A singly charged ion of mass 250 Da...
- Molecular Ion (M+)
- The intact ionised molecule with no fragmentation, formed by removing a single electron from the parent. Its m/z gives the molecular weight...
- Resolution
- The ability of a mass analyser to distinguish two ions of nearly equal m/z, defined as m/Δm at a given peak. A...
- Tandem MS (MS/MS)
- Two stages of mass selection in series with a fragmentation step in between. The first stage selects a precursor ion, a collision...
Explained in
- Mass Spectrometry: Principles, Ionisation and Mass AnalysersA mass measured to four or more decimal places, sufficient to compute a unique molecular formula. High-resolution accurate-mass (HRAM) instruments (Q-TOF, Orbi...