A field ionization and collisionally activated dissociation/charge stripping study of some [C₉H₁₀]^+˙ ions

Abstract

The extent of isomerization of [&Hlo]+' ions, with lifetimes of approximately 10-l1 and 10-6s has been investigated using field ionization, collisionally activated dissociation and charge stripping techniques. The [C9Hlo]+' ions which were investigated included the molecular ions of a-methylstyrene, P-methylstyrene, o-methylstyrene, m-methylstyrene, pmethylstyrene, indan, cyclopropylbenzene, allylbenzene and the product of water loss from 3-phenylpropanol. The field ionhation spectra of all the &Hlo hydrocarbons were different indicating that isomerization to a common ion structure had not occurred to a measurable extent for ions with lifetimes of approximately 10-l1 s. Collisionally activated dissociation and charge stripping results indicated that most of the [C&,]" ions continued to maintain unique ion structures (or mixtures of structures) at ion lifetimes of lO-'s. Possible exceptions are the [C,Hlo]+' ions from allylbenzene and cyclopropylbenzene which gave indistinguishable collisionally activated dissociation and charge stripping spectra.

On the normalization of a mass spectrum for comparison of two spectra

“…In all our studies eq 1 yields less number of hits than eq 2, indicating on the preference of eq 2. Gross and coworkers started with normalizing in relation to only one of the vectors [3] (or more accurately each component was normalized to the lower value of this component in the two spectra) and then changed to normalization with respect to the arithmetic mean of the two vectors [4]. However, even this cooperative normalization does not have any physical or mathematical meaning.…”

Differentiation of isomeric C8-substituted alkylaniline adducts of guanine by electrospray ionization and tandem quadrupole ion trap mass spectrometry

“…In this study we demonstrate the structural differentiation of thirteen C8-substituted deoxyguanosine and guanine adducts from methyl-, dimethyl-, and ethylanilines by using ESI and quadrupole ion trap mass spectrometry (QITMS) and calculation of a similarity index (SI) [6]. Our results suggest that ESI and QITMS may be used to develop a database of product ion spectra to facilitate the identification of unknown DNA adducts.…”

“…As indicated above, the SI was developed as a quantitative means of testing the similarity of two product ion spectra [6].…”

On the comparison of different tests for identification of a compound from its mass spectrum

“…However, it does not say which one of them will be better for search from the library. Thus, for example for the two close vectors (1,2,3,4,5) and (1,2.1,3,4,5) cos is 0.999916 while Pearson's r is equal to 0.999643. To see it more clearly we should look on their deviation from unity, which is the criterion for dissimilarity.…”

“…In this paper, Gross and coworkers change the definition they made earlier [5] for the similarity index. Instead of dividing by the intensity of one of the mass spectra they divide by the arithmetic mean of both spectra; however, why they take the arithmetic mean and not the geometric or the harmonic one is unknown, when all have the same unit.…”