MSD
Definition
Mass Selective Detector. GC-MS or LC-MS detector that identifies analytes by mass spectrum. The confirmation standard for drug and toxicology casework.
- Full name
- Mass Selective Detector
- Coupled to
- GC or LC
- Identifies by
- Mass spectrum
- Role
- Confirmation standard in drug/toxicology casework
Common questions
Why is an MSD considered a confirmation-level detector rather than a screening one?+
An MSD records the full fragmentation pattern of a compound, giving a spectral fingerprint that can be matched against a reference library with high specificity, unlike screening detectors that flag a class of compound without confirming exact molecular identity.
How does an MSD differ from other GC detectors like an FID?+
A flame ionisation detector measures total carbon content and gives no structural information, while an MSD fragments the molecule and records the resulting ion masses, allowing structural identification rather than just detecting that something eluted at a given retention time.
What is required for an MSD result to be courtroom-defensible?+
Laboratories typically require the spectrum to match a certified reference standard's spectrum and retention time within validated tolerances, along with adherence to accredited method validation criteria, before reporting a confirmed identification.
Related terms
- ECD
- Electron capture detector. A Ni-63 radioactive source produces a baseline electron current that is reduced when electron-affinic species (halogens, nitro groups, peroxides)...
- FID
- Flame ionisation detector. A hydrogen-air flame ionises C-H bond containing analytes and a collector electrode reads the ion current. Near-universal for organic...
- Isocratic vs Gradient Elution
- Isocratic means the mobile-phase composition stays constant through the run; simple, reproducible, but limited resolving power for wide-polarity mixtures. Gradient means the...
- Mobile Phase
- The solvent or mixture that flows over the stationary phase and carries analytes along. Polarity, viscosity and volatility set the separation; switching...
- Partition vs Adsorption
- Partition chromatography separates by differential solubility between two liquid phases (GLC, reversed-phase HPLC). Adsorption chromatography separates by surface binding to a solid...
- Plate Theory
- Model that treats a column as a series of theoretical plates. The Height Equivalent to a Theoretical Plate (HETP) measures column efficiency;...
- Rf Value
- The retention factor, defined as the distance the spot travels divided by the distance the solvent front travels on the same plate....
- Stationary Phase
- The immobile material the mixture flows past. In paper it is water inside cellulose fibres; in classical column work and TLC it...