Exploring and modelling the responses of electrospray and atmospheric pressure chemical ionization techniques based on molecular descriptors

Mass spectroscopy with two different ionization techniques, electrospray ionization and atmospheric pressure chemical ionization, optimized for cocaine, was applied to study 170 molecules. For each of the molecules, 429 molecular descriptors were calculated. The aim of this work is, on one hand, to determine whether it is possible to identify which is the better ionization technique, electrospray ionization or atmospheric pressure chemical ionization, to analyse a given molecule, based on the calculated descriptors, and on the other hand to correlate the response of each of the techniques individually with these descriptors. For each molecule, the ratio between the corrected responses of electrospray ionization and atmospheric pressure chemical ionization was used as criterion to decide which ionization technique was the better for the analysis. The chemometrical methods used to explore and model the data were Principal Component Analysis, Projection Pursuit, Classification and Regression Trees, Partial Least Squares and Stepwise Multiple Linear Regression. The results obtained did not allow establishing, based on the calculated molecular descriptors, which is the better ionization technique to analyse a certain molecule for the studied data. (c) 2005 Elsevier B.V. All rights reserved.