Mass Spectroscopy

• Liquid Chromatography Mass Spectroscopy (LC-MS): An analytical technique where compounds are separated by liquid chromatography before detection using a mass spectrometer.
• Retention Time (RT): The time taken for a metabolite/compound to elute from the chromatographic medium. RT is used to enhance a detected metabolite's annotation and identification by comparison to the RT of a known standard.
• m/z: Mass spectrometers rely on ionisation of compounds to detect them. Due to the effect of the electric fields used in mass spectrometry, compounds with a charge of greater than one act like they have half the mass, and therefore the detection scale is related to mass to charge ratio (m/z) rather than mass. Mass-to-charge-ratio values measured by the mass spectrometer.
• MS Peak: The mass-spectrum represented in two dimensions by the m/z vs the signal intensity of a compound.
• Signal Intensity (SI): Arbitrary units describing the peak height of a compound. As different molecules have different susceptibilities to ionisation, the height of the mass-spec peak is not directly indicative of the abundance of a compound.

---

Metabolomics

• Metabolism The chemical reactions (or metabolic processes) that are involved in maintaining the stasis of the cell.
• Metabolite: The small-molecule substrates, intermediates and products (compounds) of an organism’s metabolism.
• Metabolome: The collection of metabolites found in an organism, biofluid or tissue.
• Metabolomics: Comprehensive metabolite profiling of a system (cell, tissue, organism), which allows the unique chemical fingerprint (of small molecular compounds) that a metabolic process leaves behind, to be investigated.
• Metabolite Identification: Where the chemical identity of an MS peak is obtained from appropriate local reference material such as authentic chemical standards using both RT and m/z.
• Metabolite Annotation: Where the chemical identity of an MS peak is assigned based solely on matching m/z to compounds in a database (e.g. KEGG, HMDB, LipidMaps). As the annotation is based solely on mass, a single MS Peak can be annotated as numerous compounds and a single compound can be annotated as several different MS peaks.
• Fragmentation Analysis: Where the intact compound (that gives rise to the parent m/z) is dissociated into sub structures. Here, two parent ions of similar/identical masses (e.g. isomers; same chemical formula, different arrangement of atoms) may fragment differently depending on their chemical structures. This MS/MS peak fragmentation pattern can be searched against mass spectral databases to give confidence to (or dismiss) a peak/compound annotation

---

Drosophila

• Drosophila: The fruit fly, commonly used as a model organism for study of genetics and development.

---

This glossary is a work in progress and it is assumed that it will build up over the course of this project. If you have any questions about terms not listed here please contact us or leave some feedback and we will add your query to the glossary.