183 

 determining double bond positions and differentiating isomers [97-101]. These, 



however, were not used in these studies. 



The PCI parent ions of the examined aldehydes fragmented predominantly 

 by even neutral losses of 26, 28, and 30 Da. These losses have been attributed to 

 losses of ethene, carbon monoxide, and formaldehyde, respectively. Additionally, 

 fragment ions were observed at m/z 39 (CjHj^) and m/z 19 (H30^). Daughter 

 spectra produced from the selected [M +!!]■*" ion contained an intense ion at m/z 31 

 (CHjO^). Analysis of daughter spectra of the [M-H]~ ion revealed, in most cases, 

 the base peak as the selected parent ion, except in the case of benzaldehyde. A 

 neutral loss of 28 Da (CO) from the [M-H]~ ion occurs and the OH~ ion, at m/z 17, 

 may be present. 



The [M+H]^ and [M-H]^ ions of the ketones (all methyl ketones in this 

 study) fragmented by even neutral losses of 42, 30, 28, and 18 Da. These neutral 

 losses are similar to those of the aldehydes; therefore, differentiation between these 

 classes may not be possible using the rules from these analyses. An ion at m/z 33, 

 most likely protonated methanol, was produced from the [M+H]"^ ion in most cases; 

 an ion at m/z 31, most likely deprotonated methanol, was produced from the [M-H]^ 

 ion in most cases (as was also the case for the aldehydes). The negative ion 

 fragmentations were also similar to those of the aldehydes, except for the presence 

 of an ion at m/z 41 (CHCO"). 



The most studied class in the library and table are the carboxylic acids; this 

 stems from earlier analyses demonstrating the abundance and frequency of acids on 



