Variously substituted aryl ketones served as models to gain insight into the collisional-activation process in an ion-trap mass spectrometer. The effects of different targets (helium, argon) at different pressures were examined. The investigation also involved the comparison of the results of tandem mass spectrometry experiments in the ion trap with those obtained in high-energy collision and mass-analysed ion kinetic energy experiments in a sector instrument. Use of argon and low helium pressures in the ion trap results in both an increase of the average internal energy of the activated ion and, presumably, a less broad energy deposition profile. The results indicate that the maximum value of internal energy achieved by an ion through multiple collisions in the ion-trap mass spectrometer is limited by the presence of low-energy reaction channels.The quadrupole ion trap was first described by Paul and coworkers in 1958,' but its application as a mass spectrometer dates back to 1983. Since 1985, an advanced version of the ion-trap mass spectrometer (ITMS) has been commercially available (Finnigan-MAT, Bremen, FRG), which has the capability of performing tandem mass spectrometry (MUMS) experiments , using collisional activation* or ph~toirradiation~ to induce ion fragmentation. A comprehensive monograph on ion-trap devices has recently a~p e a r e d .~ Collisionally-activated dissociation (CAD) experiments are performed by irradiating the selected ion at its specific resonance frequency with a supplementary R F potential; this results in an increase of the ion kinetic energy from the millielectronvolt range, typical of ions stored in the trap, up to the electronvolt range. A great deal of work has been devoted to define the energies involved in the ITMS collisional-activation process4 and comparisons with conventional instruments have been made.5s6 Studies have also been carried out to establish the upper limit of kinetic energy that an ion can possess without being ejected from the A value of lOeV has been found to be critical for a stable motion, even if a small fraction of ions with 3 times this energy can still be trapped.' The internal energy of an ion decomposing via collisional activation depends on its kinetic energy. This can be varied by changing both the amplitude of the supplementary RF together with the resonance frequency.2 Maximum values of 3.5 and 5 eV of excess internal energy have been estimated for different systems,' under conditions, however, which produce instability for the Author to whom correspondence should be addressed. majority of the trapped ions. One important peculiarity of collisional activation in the ion trap concerns the time scale involved in these experiments. In order to obtain good parent-to-daughter conversions, times are used which are 3-4 orders of magnitude greater than those typical of sector and triple quadrupole instruments.' Under these conditions the selected ion undergoes several collisions with the bath gas during the excitation time and is subjected to stepwise act...

Vanadium oxide thin films were prepared by chemical vapor deposition using as precursors a series of vanadyl complexes of general formula VO(L) 2 (H), where L is a ␤-diketonate ligand. The depositions were carried out on ␣-Al 2 O 3 subtrates in O 2 , N 2 , and N 2 ϩ H 2 O atmospheres. In order to elucidate the role played by different ligands and synthesis conditions on the properties of the obtained films, the chemical composition of the samples was investigated by X-ray photoelectron spectroscopy, while their microstructure and surface morphology were analyzed by X-ray diffraction, Raman and atomic force microscopy. The thermal decomposition of the precursors, with particular attention to their reactivity in the presence of water vapor, was studied by mass spectrometry and Fourier transform infrared spectroscopy.

The effects of storing ions at different values of the stability parameters uz and q, were studied in a quadrupole ion trap, using helium or argon as buffer. A region was localized near the boundaries of the stability diagram in which the ions experience an increase in their kinetic energy. This is reflected in the occurrence both of fragmentation due to collisional activation and of a certain extent of ion loss due to unstable trajectories. The results of this excitation, referred to as 'boundary effects,' depend on the specific qz at which the ion storage is performed and on the buffer gas used, and point to a simpler means of obtaining tandem mass spectra with the ion trap without the need to apply resonant tickle voltages between the end-cap electrodes.

The study of electron ionization (EI) induced decomposition patterns is usually undertaken by extensive metastable-ion investigations, mainly depending on spectra of the unimolecular decomposition of parent ions carried out in double-focusing instruments.By such an approach, in the last decades most of the definitive data on ion structures and on the mass spectrometric behaviour of many classes of compounds have been achieved. Unfortunately, single-quadrupole analysers do not give any definitive information on the unimolecular decomposition pathways of selected species; only by collision experiments in triple-stage quadrupolar systems can such data be obtained.','The ion-trap mass spectrometer3 (ITMS) offers a particularly interesting mass spectrometric approach due to its ability to store ions for further experiments, first of all being mass analysis. In particular, the use of a supplementary AC voltage (the so-called 'tickle' voltage) leads to effective collision-induced decompositions of preselected ionic species, even in cases where the energy deposition into the stored ionic species is lower than that usually observed in high-energy collision experiments.For these reasons ITMS seems to be highly promising for ion structure investigations as an alternative to the more complex (and more expensive) systems such as double-focusing sector instruments and triple-stage quadrupoles. In other words, what is usually obtained by the study of natural or collision-induced decomposition in multiple-stage analysers, is achieved in the ITMS by a simple, single-stage device by means of time separation of the different steps, namely electron ionization, ionic species isolation, collision of the preselected ions, mass analysis and detection of the collisioninduced decomposition products.Following our previous mass s ectrometric investigations of flavonoid cornpounds?'in this paper we will discuss the data obtained by ITMS on structure investigation of [M -HI+ ions of chalcone (2-propen-1-ona-1,3-diaphenyl) (l), whose EI mass spectrum has + Partially and preliminarily communicated at the European Meeting on Tandem Mass Spectrometry, Manchester UK, 9-11 July 1990.* Author to whom correspondence should be addressed.already been reported together with those of some of its derivatives.6-8 In such early papers the major fragmentation pathways and rearrangement processes were used to determine the type of chalcone and, in some cases, the position of substituents on the molecular skeleton. Some disagreement was expressed concerning the structure assignment of their [M -H]+ species.Ronayne and co-workers' postulated that the commonly observed intense [M -H]+ ion of chalcone was due to the loss of hydrogen from ring A in the resonance-stabilized flavylium ion structure a. The same mechanism was also proposed by Van

It has been shown previously that collisional activation in an ion trap mass spectrometer can be achieved by storing parent ions within a narrow zone extending close to the theoretical boundaries p, = 0 or = 0 of the stability diagram. This procedure can be used for obtaining collision-induced dissociation of selected parent ions without the need to apply a precisely tuned resonant 'tickle' potential between the end-cap electrodes. In this investigation a comparison was made between the two methods ('tickle' and 'boundary') of activation based on the efficiency of parent-to-daughter conversion and on the relative abundance of daughter ions for a model system (the m/z 91p2 ratio for n-butylbenzene). The data show that, under conditions of maximum efficiency, a comparable amount of internal energy is present in the ions after activation with the two methods. However, with the 'tickle' technique it is possible to increase the internal energy of the parent ions even further, although at the expense of the efficiency, whereas in the case of the "boundary' activation, the conditions for optimum efficiency almost coincide with those for maximum activation and a drastic loss of ions follows any attempt to overcome these limits. It is also found that at any given qz value used for storing and activating parent ions the permitted mass difference between parent and fragment ions is greater with 'boundary' than with 'tickle' excitation.