57 

 Figure 2-7 is the RIC of a second bead rubbed by Dan Smith of the USD A. 



This experiment was run 30 min after the experiment which produced the RIC in 



figure 2-6. The differences in peak heights between these figures show that 



significant variations may exist between analyses from the same person. This 



difference could very well be a difference in the substances deposited on the beads, 



i.e. some substances may be retained on the skin more efficiently than others; the 



difference between figures 2-6 and 2-7 could reflect this. The difference between 



these two figures may also indicate the irreproducibility of this method of sample 



introduction. Analysis of repeated samples taken over an extended period of time 



will be addressed in Chapter 5 of this dissertation. 



Figure 2-8 shows mass chromatograms obtained from the analysis giving the 



RIC trace in figure 2-7. The ions shown are m/z values for the protonated aliphatic 



fatty acids. Specifically these are the [M-hH]^ ions for tetradecanoic acid (m/z 229), 



pentadecanoic acid (m/z 243), hexadecanoic acid (m/z 257), and octadecanoic acid 



(m/z 285). The profiles found below scan number 150 are clearly offset and depict 



the trend of this series of acids; however, without the knowledge acquired later in 



this work, the results would still be lacking in terms of identifying the full series. 



With this knowledge, some of the earlier mass spectra, such as the spectrum 



presented in figure 2-9, can be examined. Figure 2-9 is a mass spectrum from scans 



151-200 for a single bead rubbed by Dr. Anthony Annacchino. Clearly shown is the 



molecular ion for cholesterol (m/z 386) and the loss of water from cholesterol (m/z 



368). Although, the ions at m/z 200, 228, 256, and 284 correspond to the molecular 



