25 

 Single-stage detection . The triple quadrupole mass spectrometer can be used 



for single-stage mass spectrometric analyses [55]. The corresponding modes and 



operation of the quadrupoles for single-stage operation are presented in figure 1-2. 



A full mass spectrum can be acquired by either of two modes. The first quadrupole 



can be scanned, acting as the mass filter, while Q2 and Q3 are held in RF-only mode 



to pass all ions (figure l-2(a)). Alternatively, Ql and Q2 can be held in RF-only 



mode while scanning Q3, as shown in figure l-2(b). Selected ion monitoring (SIM), 



shown in figure l-2(c), is a single-stage mode allowing passage of only selected m/z 



values through the mass filter; it can be performed with either Ql or Q3. Tlie 



advantage to SIM is the sensitivity gained by scanning the quadrupole over only one 



or a few m/z values of interest [33]. 



MS/MS scan modes . The benefits of tandem mass spectrometry lie in the use 



of various modes of operation derived from the two successive stages of mass 



filtering [56]. The four modes available for MS/MS operation are shown in figure 



1-3. A daughter scan (figure l-3(a)) consists of setting Ql to a specific m/z value. 



This selected parent ion is then fragmented in Q2, the collision cell, via the presence 



of an inert gas for collision-induced dissociation. The third quadrupole (Q3) then 



scans the resultant daughter ions. Figure l-3(b) depicts a parent scan; in this 



mode, Q3 is set to pass a specific m/z value of daughter ion produced by collisions 



in Q2. As Ql scans and sequentially passes each m/z ion over the scan range, the 



data system records the intensity of the daughter ion and correlates back to the 



parent m/z value that was passed through Ql. If Ql and Q3 are both scanned with 



