Selected Ion Monitoring (SIM) mode

[okarvi]

Hi there,
Sorry for asking this very basic question. I want to determine the molecular weight of a peptide (20 AAs), using Agilent LC/MS. Can I use SIM mode to determine the exact MW of my peptide. Sometimes, I am not able to get exact mass using scan mode, but with SIM mode, it mostly gives the correct mass. Is SIM mode acceptable for publication.
Thank you all for your response.

[lmh]

what instrument are you using? "Exact mass" usually implies a ToF or similar, but SIM/scan usually implies a quadrupole...

[okarvi]

Hi, I am using Agilent 6125 LC/MSD Single Quadrupole, having both Scan and SIM mode options. I prefer to use SIM mode. Not sure if I can rely only on SIM mode. Thanks

[per_oxid]

SIM is good for quantification. For mass identification you should scan the spectra.