Resolution
Definition
The ability of a mass analyser to distinguish two ions of nearly equal m/z, defined as m/Δm at a given peak. A unit-resolution quadrupole separates m/z 500 from 501; an Orbitrap at resolution 100,000 separates 500.000 from 500.005.
- Light microscope resolution limit
- Approximately 200 nanometers
- Abbe's formula
- d = 0.61 λ / NA (where λ is wavelength, NA is numerical aperture)
- Quadrupole unit resolution
- Can separate m/z 500 from 501
- Orbitrap high resolution example
- At 100,000 resolution can distinguish 500.000 from 500.005
Common questions
What does resolution mean in forensic mass spectrometry?+
Resolution in mass spectrometry is how well the instrument can tell apart two ions with nearly identical mass-to-charge ratios (m/z). A quadrupole with unit resolution can separate m/z 500 from 501, while higher-resolution instruments like an Orbitrap at 100,000 resolution can distinguish 500.000 from 500.005. Better resolution helps identify trace compounds in forensic samples more accurately.
What limits how small objects can appear under a light microscope?+
The smallest distance between two points that can still be seen as separate is limited by resolution, given by Abbe's formula d = 0.61 λ / NA. For light microscopes, this practical limit is roughly 200 nanometers. This matters in forensic microscopy because it determines whether trace evidence like fibers or particles will appear as distinct objects or blur together.
Why does resolution matter in forensic analysis?+
In both microscopy and mass spectrometry, resolution is critical for telling the difference between similar evidence. Higher resolution lets you spot finer details in microscopic samples and identify chemical compounds more precisely when many ions are present. This direct bearing on accuracy makes resolution one of the key performance metrics for forensic instruments.
Related terms
- Accurate Mass
- 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,...
- Base Peak
- The most intense peak in a mass spectrum, normalised to 100 percent relative abundance. All other peaks in the spectrum are reported...
- Comparison Microscope
- Two compound microscope bodies connected by an optical bridge that presents one half of each body's image in a single split eyepiece...
- Depth of Field
- Axial thickness of the specimen that appears acceptably in focus at one time. High in stereoscopic microscopes, very low in oil-immersion compound...
- EDX / EDXRF
- Energy-dispersive X-ray detector attached to an SEM. Identifies elements from characteristic X-rays emitted when the beam strikes the sample. Backbone of GSR...
- Fluorescence Microscope
- Uses UV or short-wavelength excitation to make fluorophores emit longer-wavelength light. Used for semen, saliva, fibres and ink discrimination.
- 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...
- Numerical Aperture (NA)
- The product of the refractive index of the medium between objective and specimen and the sine of the half-angle of the maximum...
- Polarising Microscope
- Compound microscope fitted with a polariser below and an analyser above the stage. Used to study birefringent materials like fibres, minerals and...
- SEM
- Scanning electron microscope. Focused electron beam raster-scans the sample surface; resolution down to a few nanometres with great depth of field. Paired...
- Stereoscopic Microscope
- Two separate light paths producing a true 3D image at low magnification (typically 7x to 40x). Used for trace recovery, gross examination...
Explained in these topics
- Mass Spectrometry: Principles, Ionisation and Mass AnalysersThe ability of a mass analyser to distinguish two ions of nearly equal m/z, defined as m/Δm at a given peak. A unit-resolution quadrupole separates m/z 500 fro...
- Microscopy for Forensic Science: Polarizing, Comparison, Stereoscopic, Fluorescent and ElectronSmallest distance between two points that can still be seen as separate. Given by Abbe's d = 0.61 λ / NA. Light microscope limit is roughly 200 nm.