Glossary

Terms beginning with M

16 of 238 glossary terms.

Mobile phase: The liquid carrying the sample through the column. In peptide work typically water/acetonitrile with 0.1 % trifluoroacetic acid.
Mass accuracy: Difference between measured and theoretical mass, in ppm of the theoretical value. A relative measure — the same ppm is a different absolute error at different masses.
Mass defect: The difference between a nominal integer mass and the exact mass. Constrains which elemental compositions are plausible for an observed impurity.
Monoisotopic mass: The mass of the isotopologue in which every atom is its most abundant isotope. All theoretical masses on this site are monoisotopic.
MS/MS: Tandem mass spectrometry: selecting an ion, fragmenting it, and measuring the fragments. Required to distinguish isobaric species such as pyroglutamate from aspartimide.
Mass balance: Water + counter-ion + residual + total peptide content = 100 % of cake mass. Exhaustive and mutually exclusive. The index closes it on every record where the terms exist.
Macrolactamisation: The cyclisation step forming a lactam bridge. Incomplete cyclisation leaves the linear precursor at +18.011 Da — the commonest process failure in the melanocortin class.
Maleimide: A thiol-reactive group used for covalent conjugation, as in CJC-1295 DAC. Hydrolyses to an inert maleamic acid at +18.011 Da — pure and non-functional are compatible states.
Melt-back: A lyophilisation failure in which the cake structure is entirely lost, leaving a powder or glassy residue. Expect high residual moisture.
Metal complex: A peptide coordinating a metal ion, as in GHK-Cu and thymulin. An acidic reverse-phase mobile phase dissociates the complex on-column.
Maximum valid dilution: The greatest dilution at which an endotoxin limit can still be detected. Sets how far a sample may be diluted to overcome interference.
Membrane filtration: The preferred sterility technique: filter the article through 0.45 µm, then incubate the membrane in media.
Method suitability (sterility): Demonstration that the article does not inhibit growth of challenge organisms. Omitting it on an antimicrobial peptide produces a false pass.
Median: The 50th percentile. Preferred over the mean throughout this index because purity distributions have long left tails.
Median absolute deviation (MAD): The median of absolute deviations from the median, scaled by 1.4826 to estimate σ for normal data. Robust to outliers.
Method limited: A verification status: the method used does not meet the index specification for the compound class. The result is published with the limitation named.