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- Posts: 8
- Joined: Fri Sep 16, 2005 12:15 am
Can anybody help me what is "quadrupole mass spectrometer with ammonia negative chemical ionization and selected ion monitoring" all about? Where can i find technical assistance for this? Thanks!
A quadrupole is a type of mass analyzer, and is very common on GC-MS and LC-MS systems.
Selected ion monitoring (SIM) is a type of experiment that can be performed using a quadrupole, whereby ions of one or more user-selected m/z (mass to charge ratio) values are allowed to pass through the quadrupole and reach the detector, while all others are ejected. For example, SIM on 100 m/z means that any ion with m/z of 100 will produce signal, but an ion with any other m/z will not.
Chemical ionization (CI) is a type of ionization that can be used with mass spectrometers. A chemical reagent gas is ionized by bombardment with electrons, and the reagent ions react with neutral analyte molecules to produce analyte ions. CI can be used to produce positive or negative ions. Analyte ions produced via CI tend to fragment less than ions produced via electron ionization (EI), and thus CI is referred to as a "soft" ionization technique. In this case, your quote is referring to the use of ammonia as the reagent gas to produce negative ions.
