184 

 the skin. In the PCI mode, a neutral loss of 46 Da (formic acid) from the [M+H]"^ 



ion is commonly observed. There are small neutral losses of 1-2 Da observed from 



both selected parents produced by PCI, as well as the [M-H]~ parent ion, produced 



by NCI. The most indicative evidence for the presence of a carboxylic acid comes 



from the analysis of negative ions. A neutral loss of 44 Da (COj) is very common 



and abundant. This neutral loss often produces the base peak in the negative ion 



daughter spectrum. Unfortunately, as the relative molecular mass of the acid 



increases, the fragment ion resulting from this neutral loss is less prominent. The 



presence of ions at m/z 60 and m/z 73 (McLafferty rearrangement ions) in EI mode 



and m/z 74 from PCI with single stage detection can then be used to indicate the 



presence of acids; this is examined in Chapter 5. 



The alcohols, in positive ion mode, exhibit a significant neutral loss of 18 Da 

 (H2O), which may be the base peak in daughter spectra. The base peak of PCI 

 daughter spectra from diol and triol parent ions was the fragment ion which resulted 

 from the neutral loss of 36 Da (two water molecules). The presence of a daughter 

 ion at m/z 19 (HjO)"^ was also observed in almost all PCI produced daughter spectra. 

 An indicator of straight chain alcohols in the negative ion mode is the presence of 

 the base peak formed by a neutral loss of 2 Da (Hj). Additionally, a fragment ion 

 at m/z 17 (OH~) is commonly observed. 



The examined amines demonstrated an odd neutral loss of 17 Da (NH3) in 

 the positive ion mode. This loss commonly formed the base peak of the daughter 

 spectra. Additionally, an ion at m/z 18 (NH4'^) may be present in the PCI daughter 



