Dr. Robert Haufler
Staff Research Scientist, Sciex
Robert Haufler, Ph.D., is Staff Scientist who develops time-of-flight technology at the Concord, Ontario, Canada facility (Since 2006). Dr. Haufler was previously employed at PPD (a CRO in Richmond Virginia, USA) as Group Leader. Prior to that, Dr. Haufler worked for several startups in mass spectrometry and fullerene research and production.
Dr. Haufler earned his Ph.D. at Rice University in Houston Texas working in the fullerene research group with Richard Smalley and Bob Curl.
Time of flight mass spectrometry, Zeno trapping and EAD
Time-of-flight (TOF) is an excellent technique for high resolution mass spectrometry. The advantages are speed and sensitivity. Also, unlike scanning techniques such as magnetic sector mass spectrometry or quadrupole mass spectrometry, the full scan range is obtained. The time-of-flight technique creates spectra in momentary acquisitions, snapshots so to speak. This works quite well for pulsed ionization such as MALDI. In this case, all ions are fully utilized, each ionization event produces spectra. When the ion beam is continuous, as typically is the case in electrospray, losses occur. It takes a bit of time to separate ions in the time-of-flight spectrometer. While this happens, following ions cannot be utilized.
Zeno trapping corrects this problem. It does so by staging ions fed by the beam prior to injection into the time-of-flight analyzer. This must be done in a way that avoids any mass/charge bias. Because ions are necessarily transferred from the zeno trap to the TOF analyzer by constant energy, low mass/charge ions will move faster than high mass/charge ions. To arrange for the ions across the entire mass/charge range to arrive simultaneously at the TOF analyzer, the heavy ions are released in the order of heavy to light. This has been accomplished and has demonstrated to recover all losses. Zeno trapping can be switched on and off rapidly. Fast enough to allow it to be activate or deactivate during the acquisition of data for an LC chromatogram. This allows ion signal to be kept at the optimal intensity for the detection system. Zeno can be activated when the signal is low and deactivated when the signal is high. Zeno is especially helpful with EAD (electron activated dissociation). EAD is a very helpful alternative method of fragmentation that produces fragments complementary to collisionally induced dissociation (CID). A challenge is that the yield is sometimes low. The duty cycle losses that are recovered using zeno helps this problem.
