Of particular note is the increasing use of ion-trapping techniques—both Fourier transform ion cyclotron resonance (FT-ICR) and quadrupole ion trap mass spectrometry (QITMS)—in analytical MS. At the 1981 symposium only one paper concerning ion traps was presented; in 1990 almost onethird of the presentations used ion traps in some form. Ion traps are unique in the control they allow over the mass and energy of ions stored for extended periods of time; thus, ionneutral interactions can be enhanced and the resulting gas-phase processes studied. Sequential stages of MS analysis (i.e., MS/MS/MS . . . MS") can also be performed, extending the analytical capabilities of ion-trapping techniques. Fundamental studies of the effect of the various trapping parameters—such as pressure, time, and excitation—on the resultant mass spectra of simple to complex molecules could be considered a subtopic of this year's symposium. James Gord from Purdue University studied the dynamics of the reaction between the cations of several transition metals and benzene. Measurement of the product ion translational energies provided details of the potential energy surfaces of the reactions (1). Such detail will aid in understanding the fragmentation of larger, more complex molecular systems in FT-ICR mass spectrometers. Jennifer Brodbelt-Lustig from the University of Texas used a QIT mass spectrometer to study the degree of adduct formation and subsequent dissociation and reactivity of a series of small molecular systems (e.g., oxyaromatics). These studies lend insight into the changes in the ion populations as a function of reaction time, sample pressure, and excitation voltages (2). Ben Freiser of Purdue University described the combination of lasers and MS as the "perfect marriage." Indeed, lasers of all varieties (dye, CO2, Nd:YAG) are becoming more popular as ionization, desorption, and photodissociation sources with trapping and other mass spectrometric techniques. Freiser used lasers and FT-ICR to study potential energy surfaces, kinetic energy releases, and collisional and radiative relaxation rates for transition metal complexes. The first stable, doubly charged mixed metal dimer, LaFe 2 + , was observed by photodesorption of La 2 + and subsequent reaction with FeC0 5 to produce LaFe(CO)| + followed by argon collision-induced dissociation (CID) to give the doubly charged metal dimer (3). Murray Johnston from the University of Delaware used a coherent source
of vacuum-ultraviolet (vacuum-UV) radiation (Nd:YAG laser tripled twice to 118 nm [10.5 eV]) with a time-offlight (TOF) mass spectrometer to study neutral decomposition chemistry by first photodecomposing a neutral gas-phase species and then photoionizing the decomposition products. The main drawback of laser systems is their relatively high cost; thus, Dave Russell's studies obtained with a $3000 N2 laser on a new hybrid EB TOF mass spectrometer were received with great interest. The introduction of these lowcost N2 lasers may bring about even greater use of lasers in MS studies (4). Paralleling the growth of lasers is a resurgence in the use of TOF mass spectrometers, as seen in the work of Russell and Johnston. The intrinsic pulsed operation and low cost of TOF mass spectrometers make them attractive counterparts in laser studies. Further studies using a laser TOF mass spectrometer were presented by Bob Cotter from The Johns Hopkins University, who performed both IR and UV matrix-assisted laser desorption (LD)-TOF-MS with a pulsed extraction lens to study the mass spectra of biomolecules up to 116 000 Da (0-galactosidase of E. coli) (5). John
Boyle of Yale University coupled a ceramic microjet reactor designed by John Fenn to a TOF mass spectrometer with vacuum-UV photoionization to study stable and labile combustion intermediates. Analysis of high-mass molecules At the 1981 summer symposium, compounds ranging from 1000 to 10 000 Da were considered to be "high mass." Today, biomolecular species 10 times that weight are being analyzed. As the mass range accessible to MS continues to increase, there will be a greater demand for successful interfacing of separation and ionization techniques t h a t are amenable to answering questions of biochemical concern. Dick Smith from Pacific Northwest Laboratory illustrated the current capabilities of capillary zone electrophoresis/electrospray ionization (CZE/ES) MS in biomolecular analysis by presenting the structurally specific spectra of a 23-fmol sample of cytochrome c (6). He found that for well-behaved systems, the charged states are sufficiently resolved to permit molecular weight determination with precision of < 0.001% in the 100-kDa range. Currently, however, CZE/ES is limited by the large background currents arising
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ANALYTICAL CHEMISTRY, VOL. 62, NO. 21, NOVEMBER 1, 1990 • 1115 A
