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ASMS φ Heats up ATLANTA
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his year's American Society for Mass Spectrometry (ASMS) Con ference on Mass Spectrometry and Allied Topics, the 43rd in the series, was one of the busiest ever. Held in At lanta May 21-26, the conference fea tured five concurrent symposia per day, up from four per day for the 1993 confer ence. Daily poster sessions and evening workshops were heavily attended and very lively, as were thefivemorning ple nary sessions. The conference organizers placed a strong emphasis this year on MS educa tion. One new addition to the general pro gram was a series of four "Basics of" style tutorials, presented alongside the af ternoon symposia sessions. Organized by Brian Musselman of JEOL USA, these tutorials covered the basic theory and practical aspects of using electron impact and chemical ionization on a quadrupole mass analyzer, fast atom bombardment MS on a sector instrument, matrixassisted laser desorption/ionization-timeof-flight MS (MALDI-TOFMS), and electrospray ionization (ESI) with an ion trap. Helping conferees keep up with all of this was a searchable computerized confer ence program complete with abstracts for oral and poster presentations. The plenaries began Monday with a lecture by Robert Watson of the Office of Science and Technology Policy; he ad dressed science and technology's role in
mit Murray of Emory University (GA) for New applications, his development of an interface for aero sol MALDI-MS and to Lee Sunderlin of instrument Northern Illinois University for tandem MS studies of alkali metal-crown ether combinations, and complexes. The 1995 ASMS Award for Distinguished Contribution to Mass Spec ionization techniquestrometry went to Keith Jennings of the of Warwick (U.K.) for his devel were introduced at University opment of collision-induced dissociation (CID; also known as collisionally activated this year's ASMS decomposition, or CAD) as a fragmenta tion technique without which most tan conference dem MS methods would not be possi balancing economic growth and environ mental safety. Don Catlin of the UCLA Olympic Analytical Laboratory spoke Tuesday morning on MS methods in sports drug testing. Multimedia presenta tions followed on Thursday; R. Graham Cooks of Purdue University (IN) pre sented real-time simulation movies of molecular motion in an ion trap. The week wrapped up with an entertaining (and eye-opening) Friday morning talk by CNN science correspondent Miles O'Brien on "The Geek Factor: Why TV Networks Scoff at Science News," which he illus trated with video clips of typical science coverage in news broadcasts. At the awards ceremony Wednesday morning, Christie Enke of the University of New Mexico presented the 1995 corpo rate-sponsored research awards to Ker-
ble. In his plenary lecture, Jennings re called that his work on CID stemmed from an exploration of the process of metastable fragmentation. In the early mass spectrometers, he said, "There was a question of whether metastable frag mentation was an internal process or whether it was collisionally induced. We took up the problem and did CID on pur pose." When soft ionization methods came along, he said, CID became an important tool for acquiring structural information from selected precursor ions. Using CID with B/E linked scan techniques in a foursector mass spectrometer, it was possi ble to identify either all the products of a selected precursor or all precursors of a given product. The oral and poster presentations on analytical MS topics focused primarily on instrumentation, methods, and applica-
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tions. Fundamental gas-phase ion chemistry was also featured in three symposia and several evening workshops, and echoes of this topic made their way into several of the analytical talks, particularly with regard to the role of (now commonly available) multiply-charged ionization methods in expanding the fragmentation efficiency of CID for very large ions at low or high energy. Attention has shifted from some of the hot topics of two years ago (MALDI vs. ESI) ion traps, protein and DNA sequencing, MS libraries, etc.) to more comprehensive approaches for real-world sample applications and to novel combinations of ionization sources and mass spectrometers. There may even be a completely new type of mass spectrometer on the horizon, if the prototype shown in one Thursday poster can be refined without breaking the computer memory bank. Instrumentation The polarization of support between ESI and MALDI has dissipated somewhat. As both soft ionization methods have become more popular and more routinely available, the advantages of each (i.e., accommodation of clean vs. dirty samples, continuous vs. pulsed operation) have made them both desirable for protein and polymer work. Continuous-flow ESI methods for quadrupole or sector MS and LC/ MS, along with discontinuous MALDI methods for TOFMS, are now fairly standard combinations. However, the sweeping changes taking place in the MS instrument market, particularly the decline in manufacture and sales for sector instruments, are pushing the development of cross-bred instruments and ones that can accommodate both types of ion sources interchangeably. ESI was featured with TOF systems in a few presentations, and MALDI was paired with sector MS in a few more with the help of static or scanning integrating array detectors. The quadrupole ion trap-TOF combination, originally reported by David Lubman earlier this year, was featured in several talks and posters, as were sector-TOF instruments for MS/MS. More common were oral and poster presentations of MALDI and ESI ion source configurations for Fourier transform-ion cyclotron resonance (FT-ICR) 494 A
MS. The establishment of MALDI and ESI for soft ionization of large delicate molecules provides an ideal application for exploiting the high mass resolution and accuracy of FTMS and its ability to perform MS4. However, because of compatibility problems caused by the strong magnetic field of the analyzer and the difference in vacuum requirements between the ICR ion trap and the ion sources, most configurations for FT-ICRMS leave the source outside the magnet core. These externalsource designs make it easier to change sources, but they require a way to transfer the ions into the ICR trap and are therefore susceptible to transmission losses. Richard Smith's group at Pacific Northwest Laboratory and others presented configurations with the sources placed inside the magnet and with differential pumping for the source and trap.
The most unusual instrument was a prototype for massively parallel MS. Quadrupole ion trap MS methods are being developed for a variety of routine applications, but the dependence of ion frequencies on ion population can cause unpredictable frequency shifting behavior, resulting in ion.mass displacements. Ion frequency shifting in quadrupole ion trap MS was explored by a number of researchers, including Timothy Griffin and Richard Yost of the University of FloridaGainesville and Frank Londry and R. E. March of Trent University (Canada). Perhaps the most unusual instrument presentation was a Thursday afternoon poster by Efim Dynin and Nicholas Kirchner of MPIi (San Jose, CA) that featured a prototype design for a "massively parallel" mass spectrometer. Using an ion trajectory simulation, the researchers designed a new type of mass spectrometer that consists of a stacked array of small chicken-wire-like metal grids with individually applied computer-controlled radio frequencies and dc voltages. The shape of
Analytical Chemistry, August 1, 1995
the ion pipe of effective potentials through the stacked grids can be manipulated to control ion movement and can act as a static lens. If the array can be expanded and control and data processing can be refined, said Kirchner, possible applications for the inexpensively fabricated instrument with disposable individual grids include benchtop LC/MS. Ionization This year, MALDI was featured more frequently than any of the other ionization techniques and garnered more posters than any other single poster category. Aside from hyphenation with FTMS, two developments in MALDI stand out this year. One, "pulsed ion extraction" (or "time lag focusing" or "delayed ion extraction"), is not a new idea for improving the mass resolution of MALDI-TOFMS, but rather a revisitation of Wiley and McLaren's 1955 experiments with modern electronics control. Pulsed ion extraction works by creating a coordinated time lag between laser desorption/ionization from the sample probe and voltage-mediated acceleration or "extraction" of the ions into the mass analyzer. This corrects for small differences in ionization times within the ion population of a single laser shot and focuses the ions prior to acceleration. Marvin Vestal of PerSeptive Biosystems presented MALDI-TOF mass spectra of an RNA 12-mer with mass resolution of 8000 and of singly-charged bovine insulin with mass resolution up to 12,500, nearly comparable to that of a sector instrument, using a prototype delayedextraction design. The second development, reviewed in a Tuesday oral session by Franz Hillenkamp of the University of Muenster (Germany) , is the use of IR lasers with matrices such as frozen glycerol and even ice. IR lasers have been used for MALDI since 1990, but they are much less common than UV or visible-region lasers because they are more expensive and fewer matrices are available. IR lasers consume 10100 times more material per shot than UV lasers do for comparable signal intensity, but can reduce metastable decay for some analytes and can increase mass resolution for MALDI-TOFMS, Hillenkamp said. As inexpensive C0 2 lasers become available, he predicted, IR MALDI should become more popular.
The classic question of how ions are formed by ESI was reexamined by Paul Kebarle and John Fenn. However, theory was supplemented this time around with some innovative methods for looking at ionization trends. Feimeng Zhou of Gary Van Berkel's lab at Oak Ridge National Laboratory likened the ESI source to a controlled-current electrolytic cell because redox reactions sometimes occur between the analytes and the interior metal surface of the nebulizer. The role of analyte concentration in ESI ion yield and charge state distribution was also explored by a number of speakers, including Brad Coopersmith of Sandoz Pharmaceuticals and Richard Cole of the University of New Orleans. Another soft ionization technique featured for FTMS was massive cluster impact ionization (MCI), which entails bombarding a sample embedded in an NBA or glycerol matrix with large, multiplycharged glycerol clusters at high impact energies. Paul Speir of Bruker Analytical Systems demonstrated gentle desorption of bovine angiotensin II, insulin, and ubiquitin peptides with multiple charges, noting that MCI appears to combine features ofbothMALDIandESI. The ability to place multiple charges on molecules led to several discussions on the need to expand precursor ion fragmentation techniques. Multiple charging may be especially useful for obtaining complete structural information from large molecules, because it can increase the efficiency of fragmentation at lower energy. Robert Hettich of Oak Ridge National Laboratory compared CID with more recently developed precursor ion dissociation techniques such as sustained off-resonance irradiation and multiple excitation collisional activation for oligonucleotide sequencing in a MALDI-FTMS system. Applications The applications symposia branched out this year from the primary areas of biochemical (mostly protein and glycoprotein) and inorganic MS to areas such as immunology, industrial polymer characterization, regulatory petrochemical analysis, and environmental monitoring, where MS structural determinations are becoming more important to confirming pollutant identity.
Immunological applications of MS were presented in a Thursday oral session. Approaches varied from microcapillary LC/ESIMS characterization of proteins and peptides for important immunological processes such as graft versus host disease (e.g., bone marrow rejection) to a "mass spectrometric immunoassay" that combined immunoaffinity capture with MALDI-TOFMS. Polymer characterization was the focus of a Monday symposium. Surface characterization by imaging TOF-surface ionization MS was presented by David Briggs of ICI Materials and by Stefan Reichlmaier of Physical Electronics. Other talks focused on MALDI-MS determination of MW distributions, endgroups, and masses of oligomer repeat units. A Tuesday poster by Jim Via of Morton Intl. described the use of SFC/chemical ionization MS with direct fluid introduction for
Multiple-charge ionization may help large molecules fragment at lower collision energies. the determination of monomers and polymer hydrolysis products. Petrochemical analyses included the characterization of porphyrins and GC/MS multianalyte determinations of oxygenates and aromatic hydrocarbons in reformulated fuels. Environmental applications in a Tuesday symposium included ion trap MS of halogenated organic byproducts of drinking water chlorination, presented by William Budde of the Environmental Protection Agency and others, and MS/MS CID fragmentation of pesticides (Jehuda Yinon, Weizmann Institute of Science, Israel). A Wednesday session focused on atmospheric analytes such as H 3 0 + , S0 3 , and hydrochlorofluorocarbons. George Managadze of the Russian Academy of Science Space Research Institute (Moscow) described three new TOFMS instruments developed for on-board and landing module installations on the PHOBOS and SOHO missions.
Bioanalytical applications were not limited to proteins and peptides. Pharmacological applications included capillary electrophoresis (CE)/MS and CE/MS/MS (Stephen Naylor, Linda Benson, and Andy Tomlinson, Mayo Clinic, MN), and several LC/MS separations using APCI and ESI. There were also a greater number of DNA and carbohydrate analyses by MALDI-TOFMS, including a presentation by Michelle Buchanan of Oak Ridge National Laboratory of a bacterial diagnostic assay based on MS of polymerase chain reaction-amplified DNA. A Monday symposium on elemental and isotopic analysis featured methods such as inductively coupled plasma (ICP)ion trap MS (Charles Barrinaga, Gregory Eiden, and David Koppenaal of Pacific Northwest Laboratory), glow discharge ion trap MS with filtered noise fields (Douglas Duckworth, David Smith, Douglas Goeringer, and Scott McLuckey of Oak Ridge National Laboratory), and anodic stripping voltammetry/ICPMS (Gary Van Berkel, Feimeng Zhou, Douglas Duckworth, and Shelby Morton). An ICP/FT-ICRMS instrument was also featured in a Thursday poster by John Eyler's group at the University of FloridaGainesville. GLP As MS moves into the regulatory testing arena for pharmaceuticals, environmental monitoring, and characterization of reformulated fuels, the legal pressures for uniform validation procedures are growing. A well-attended evening workshop and a Friday symposium on good laboratory practice (GLP) were valuable for mass spectrometrists working in these fields, said one conferee from a pharmaceutical company, in part because GLP for MS is not currently uniform. "The workshop leader pointed out that this is a chance for the people who do MS to help determine what the validation protocols will be," she said. Nominations are being sought for the 1996 ASMS Award to be presented next year at the 44th ASMS Conference, May 12-17, in Portland, OR. Those interested in making a nomination for the award may contact Judith Sjoberg, ASMS, 1201 Don Diego Ave., Santa Fe, NM 87505; 505-9894517. Deborah Noble Analytical Chemistry, August 1, 1995 495 A
