CHEMOMETRIC APPROACH TO EVALUATE THE PARAMETERS AFFECTING THE DETERMINATION OF REACTION-RATE CONSTANTS BY ION-TRAP A LASS SPECTROMETRY

The effects of experimental parameters on kinetic measurements perform ed with an ion trap mass spectrometer have been investigated by a chem ometric approach using Experimental Design techniques. The selected ex periment was the determination of the rate constant of the reaction CH 3CO++CH3COCH3 --> CH3CO(H)CH3++CH2CO. In a first step, eight variables were studied: temperature, acetone pressure, buffer gas pressure, met hod of ion selection, ionization start mass, ionization time, mass ran ge, and reaction time. The results show that isolation method and reac tion time were the only parameters affecting rate constants determinat ion, although temperature may be considered a ''borderline'' factor. T he remaining parameters and their interactions do not significantly af fect the kinetic measurements. A second series of runs was performed t o check again the effect of reaction time, temperature, and ionization time in experiments with or without ion selection in order to compare the results of the present work with those obtained in a similar stud y on a Fourier transform-ion cyclotron resonance instrument. (C) 1998 American Society for Mass Spectrometry.