APPENDIX 

 CARBON DIOXIDE AS A CI REAGENT GAS 



Introduction 



This appendix is a compilation of background information and preliminary 

 experiments involving carbon dioxide as a reagent gas for CI. Coverage in this 

 appendbc is mainly directed towards the use of COj for production of thermal 

 electrons for electron capture negative ion chemical ionization (ECNCI); however, 

 discussion of charge exchange (CE) for positive ions is also included due to the 

 predominant use of CO2 as a charge exchange reagent gas. 



The examples included in this appendix pertain to optimization of 

 CO2/ECNCI on the TSQ70, background ions present in positive CO2/CE and 

 negative CO^/ECNCI mass spectra, and illustrations of difficulties encountered in 

 these experiments. Due to time constraints, it was not possible to conduct a 

 complete exploration of CO2 as an electron moderator for ECNCI experiments 

 related to the analysis of volatile skin emanations. Attempts to replace CH4 with 

 CO2 as the reagent gas were not successful with the sampling method and detection 

 scheme used for analyses in Chapter 5. The abundance of acid eluents in the ion 

 source led to self-CI reactions. Removal of acids by the purge and trap system 

 described in Chapters 2 and 5 would be beneficial for subsequent attempts at 



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