Spectrometers with several quadrupoles in tandem

Diagram of a triple quadrupole instrument. The first and the last (Q1 and Q3) are mass spectrometers. The centre quadrupole, q2, is a collision cell made up of a quadrupole using RF only. The quadrupole mass spectrometers are symbolized by upper case Q, and the RF-only quadrupoles with a lower case q. 

Different scan modes for a tandem mass spectrometer. 

When the gas is reactive, ion-molecule reactions can be induced. The reaction products are then analysed by the quadrupole Q3. 

The first scanning mode consists of selecting an ion with a chosen m/z ratio with the first spectrometer. This ion collides inside the central quadrupole and reacts or fragments. The reaction products are analysed by the second mass spectrometer. This is a fragment ion scan or product ion scan . This method used to be called a daughter scan . 

The second possibility consists of focusing the second spectrometer (Q3) on a selected ion while scanning the masses using the first spectrometer (Ql). All of the ions that produce the ion with the selected mass through reaction or fragmentation are thus detected. This 

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