158 



[83,87,88]. Therefore, the set of conditions for the daughter library and subsequent 



analyses need to remain constant throughout to obtain reproducible daughter 

 spectra. The daughter library allowed for determining the specific daughters and 

 neutral losses for particular compounds and compound classes. This information 

 provided the basis for additional spectral interpretation of daughter spectra as well 

 as provided the information on specific neutral losses associated with compound 

 classes. An additional note of interest is the extensive examination of negative ion 

 fragmentations, as well as those of more typical positive ions, used in this 

 dissertation. Analysis of compound classes by positive ions remains more prevalent 

 than the use of negative ions [89-91]. There are some cases, e.g. for ethers and 

 carboxylic acids, where negative ion analysis yields better results than positive ion 

 analysis [92-95]. 



Compound Class Screening 



The final part of this chapter is focused on applying the information on 

 neutral losses obtained from the daughter library for rapid compound class screening 

 of samples of human skin emanations which have been desorbed off of handled glass 

 beads. The actual screening employs cryo-focusing of desorbed volatiles and GC 

 separation. The sample introduction used for MS/MS screening by neutral losses is 

 also employed for almost all work pertaining to compound identification by GC/MS 

 (addressed in Chapter 5). 



