22 

 CI, negative ion chemical ionization (NCI) provides additional molecular weight 



information, and in some cases structural information. The concept of CI will be 



addressed in Chapter 5; informative structural information derived from NCI is 



examined in Chapter 3. 



Triple quadrupole mass spectrometry 



The first report of a triple quadrupole mass spectrometer for chemical 

 analysis occurred in 1978 by Yost and Enke [54]. Figure 1-1 depicts a schematic of 

 a triple quadrupole system. This figure is representative of the Finnigan MAT 

 TSQ70 utilized throughout this dissertation. Although this instrument is still called 

 a triple quadrupole, the second quadrupole (Q2) has been replaced by an RF-only 

 octopole for better transmission of ions. 



The ion source allows for passage of an electron beam from the filament to 

 the collector. The electron beam is orthogonal to the vacuum-lock entrance 

 (allowing for probe insertion) and to the GC transfer line. The TSQ70 ion source 

 contains removable ion volumes which can be chosen to give either CI or EI 

 operating conditions. Ions generated in the source are extracted into the first 

 quadrupole mass filter (Ql) by a set of three lenses. The collision cell (Q2) is 

 housed in an assembly such that a suitable inert gas can be leaked into it. Tlie inert 

 gas functions to fragment ions via collision-induced dissociation. Resultant ions are 

 then passed into the second quadrupole mass filter (Q3). Subsequently, detection 

 is accomplished via a conversion dynode (biased for either positive or negative ions) 

 prior to amplification by the electron multiplier. 



