Chemistry Labs

Analytical chemistry

High-resolution mass spectrometry

Accurate mass and resolving power distinguish ions that share the same nominal mass.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionIntuition: the measurement idea

High-resolution mass spectrometry measures mass precisely enough to distinguish ions that have the same nominal mass. The closer two masses are, the greater the resolving power required.

Explore the High-resolution mass spectrometry measurement concept in this interactive signal.

SchoolSchool level: signal and result

Exact mass comes from atomic mass differences; resolving power is the ability to separate close masses, and mass accuracy links the measured mass to an elemental formula.

Definition:

Accurate mass and resolving power distinguish ions that share the same nominal mass.

First identify the measurand, choose a signal that responds to it, and compare the sample with a calibrated standard or a validated model.

R=mΔmR=\dfrac{m}{\Delta m}

Example: Worked analytical example

Calculate the analyte result from the stated measurement and method relation.

Solution

N₂⁺• (28.0061) and CO⁺• (27.9949) have nominal m/z 28 but differ by 0.0112 Da.

Method checkpoints
StagePurpose
PrepareControl matrix and contamination
MeasureAcquire a calibrated response
ValidateCheck recovery and uncertainty

UndergraduateUniversity: quantitative method

Resolving power measures the ability to separate close masses; exact mass identifies elemental composition because nuclei have non-integer mass defects. Fourier-transform and Orbitrap instruments exploit time-domain signals to achieve very high resolution.

Calibration, selectivity, sample preparation and uncertainty belong to the method itself, not to afterthoughts. Report units, conditions and the calibration range.

R=mΔmR=\dfrac{m}{\Delta m}

AdvancedAdvanced: physical and chemical limits

Orbitrap and Fourier-transform ion cyclotron resonance instruments convert ion motion into frequency and achieve very high resolving power. Isotope fine structure, adduct formation and calibration determine whether accurate mass can assign a formula unambiguously.

ResearchResearch frontier

Research pushes resolving power, mass accuracy, isotopic fine structure, ion mobility coupling and data processing, allowing elemental formulas and complex mixtures to be resolved at very low abundance.

References