Peptides to 40 mmu without an internal standard and to 5-10 mmu with an MALDI instruments are capable of routinely delivering mass accuracy for Several of the most popular triple quadrupole instruments that we have worked with.Īs stated previously a mass spectrometer can never be too accurate or While we believe their reports, in our experience we have been unwilling to claim better than 100 mmu accuracy for Scientists using their quradrupole instruments to obtain exact mass, and Some scientists attempt to push their quadrupole mass spectrometers to MALDI TOF and ESI time of flight type instruments. Molecule is known and a minor unknown change needs to beĮxact mass traditionally has been obtained by Exact mass is especially useful when a large part of the With other analytical analyses and in this case it becomes a valuable This information can be used in conjunction This is not to say that exact mass of larger It is difficult to determine theĮlemental composition of larger entirely unknown molecules. Reduce the size of the unknown portion of the compound, also if functional groupsĬan be identified these masses can be subtracted from the measured mass to help As mentioned above if the unknown is a protein, an enzyme digest may help
Possibilities is to reduce the size of the unknown portion of the With increasing mass the number of elemental combinations In this case for the purpose of elemental composition determination exact mass measurements are performed on moleculesīelow 500 amu with a required mass accuracyĪt or better than 5 mmu. Higher mass accuracy is always helpful. Measurement for a molecule which is essentially unknown is very difficult.
Determining elemental composition from an exact mass Little bit of knowledge about the molecule can help you restrict the number of returns obtained from an elementalĬalculator. Small molecule, what are the functional groups?" Use UV, IR, NMR, chemical modification, enzymeĭigest, or N-terminal protein sequencing to try and answer a few of Protein?", "Is it a small molecule?", "If it is a It helps to know as much as possible about Mass Measurement and Elemental Composition DeterminationĬomposition for an unknown compound from an exact mass measurement
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