Distance-of-Flight Mass Spectrometry: What, Why, and How?

Distance-of-flight mass spectrometry (DOFMS) separates ions of different mass-to-charge (m/z) by the distance they travel in a given time after acceleration. Like time-of-flight mass spectrometry (TOFMS), separation and mass assignment are based on ion velocity. However, DOFMS is not a variant of TOFMS; different methods of ion focusing and detection are used.

Inductively Coupled Plasma Zoom-Time-of-Flight Mass Spectrometry.

A zoom-time-of-flight mass spectrometer has been coupled to an inductively coupled plasma (ICP) ionization source. Zoom-time-of-flight mass spectrometry (zoom-TOFMS) combines two complementary types of velocity-based mass separation. Specifically, zoom-TOFMS alternates between conventional, constant-energy acceleration (CEA) TOFMS and energy-focused, constant-momentum acceleration (CMA) (zoom) TOFMS.

The Analog Revolution and Its On-Going Role in Modern Analytical Measurements.

The electronic revolution in analytical instrumentation began when we first exceeded the two-digit resolution of panel meters and chart recorders and then took the first steps into automated control. It started with the first uses of operational amplifiers (op amps) in the analog domain 20 years before the digital computer entered the analytical lab. Their application greatly increased both accuracy and precision in chemical measurement and they provided an elegant means for the electronic control of experimental quantities.

Distance-of-Flight Mass Spectrometry with IonCCD Detection and an Inductively Coupled Plasma Source.

Distance-of-flight mass spectrometry (DOFMS) is demonstrated for the first time with a commercially available ion detector-the IonCCD camera. Because DOFMS is a velocity-based MS technique that provides spatially dispersive, simultaneous mass spectrometry, a position-sensitive ion detector is needed for mass-spectral collection. The IonCCD camera is a 5.

Zoom-TOFMS: addition of a constant-momentum-acceleration "zoom" mode to time-of-flight mass spectrometry.

In this study, we demonstrate the performance of a new mass spectrometry concept called zoom time-of-flight mass spectrometry (zoom-TOFMS). In our zoom-TOFMS instrument, we combine two complementary types of TOFMS: conventional, constant-energy acceleration (CEA) TOFMS and constant-momentum acceleration (CMA) TOFMS to provide complete mass-spectral coverage as well as enhanced resolution and duty factor for a narrow, targeted mass region, respectively. Alternation between CEA- and CMA-TOFMS requires only that electrostatic instrument settings (i.

Constant-momentum acceleration time-of-flight mass spectrometry with energy focusing.

Fundamental aspects of constant-momentum acceleration time-of-flight mass spectrometry (CMA-TOFMS) are explored as a means to improve mass resolution. By accelerating all ions to the same momentum rather than to the same energy, the effects of the initial ion spatial and energy distributions upon the total ion flight time are decoupled. This decoupling permits the initial spatial distribution of ions in the acceleration region to be optimized independently, and energy focus, including ion turn-around-time error, to be accomplished with a linear-field reflectron.

Interleaved Distance-of-Flight Mass Spectrometry: A Simple Method to Improve the Instrument Duty Factor.

Distance-of-flight mass spectrometry (DOFMS) is a velocity-based, spatially dispersive MS technique in which ions are detected simultaneously along the plane of a spatially selective detector. In DOFMS, ions fly though the instrument and mass separate over a set period of time. The single flight time at which all ions are measured defines the specific m/z values that are detectable; the range of m/z values is dictated by the length of the spatially selective detector.

Jim Morrison, Friend and Colleague.

Our long-time association with Jim Morrison and the work that came from it is the result of a series of fortunate coincidences. We are pleased to be able to share recollections here of our interactions with Jim and how his life and work have influenced us and the field of mass spectrometry.

How constant momentum acceleration decouples energy and space focusing in distance-of-flight and time-of-flight mass spectrometries.

Resolution in time-of-flight mass spectrometry (TOFMS) is ordinarily limited by the initial energy and space distributions within an instrument's acceleration region and by the length of the field-free flight zone. With gaseous ion sources, these distributions lead to systematic flight-time errors that cannot be simultaneously corrected with conventional static-field ion-focusing devices (i.e.

Extension of the focusable mass range in distance-of-flight mass spectrometry with multiple detectors.

Rationale: Distance-of-flight mass spectrometry (DOFMS) is a velocity-based mass separation technique in which ions are spread across a spatially selective detector according to m/z. In this work, we investigate the practical mass range available for DOFMS with a finite-length detector.

Methods: A glow-discharge DOFMS instrument has been constructed for the analysis of atomic ions.

Distance-of-flight mass spectrometry: a new paradigm for mass separation and detection.

Distance-of-flight mass spectrometry (DOFMS) offers the advantages of physical separation of ions, array detection of ions, focusing of initial ion energy, great simplicity, and a truly unlimited mass range. DOFMS instrumentation is similar to that of time-of-flight mass spectrometry (TOFMS) and shares its ion-source versatility, batch analysis, and rapid spectral-generation rate. With constant-momentum ion acceleration and an ion mirror, there is a time at which ions of all mass-to-charge values are energy focused at their particular distances along the flight path.

Resolution and mass range performance in distance-of-flight mass spectrometry with a multichannel focal-plane camera detector.

Distance-of-flight mass spectrometry (DOFMS) is a velocity-based mass-separation technique in which ions are separated in space along the plane of a spatially selective detector. In the present work, a solid-state charge-detection array, the focal-plane camera (FPC), was incorporated into the DOFMS platform. Use of the FPC with our DOFMS instrument resulted in improvements in analytical performance, usability, and versatility over a previous generation instrument that employed a microchannel-plate/phosphor DOF detector.

First distance-of-flight instrument: opening a new paradigm in mass spectrometry.

A new instrumental concept, distance-of-flight mass spectrometry (DOFMS), is demonstrated experimentally. In DOFMS the mass-to-charge ratio of ions is determined by the distance each ion travels during a fixed time period; the mass spectrum is then recorded with a position-sensitive detector. The DOF approach provides a new way to separate and quantify components of complex samples.

Undetected components in natural mixtures: how many? What concentrations? Do they account for chemical noise? What is needed to detect them?

By definition, information about the set of components in a complex mixture below the detection limit is not directly available. However, if the composition of natural mixtures follows a natural law, the application of this law would enable the prediction of analytically important characteristics of that "hidden" fraction of the mixture. We have found that the analytical responses of compounds in three disparate natural mixtures (extracellular metabolites, light crude oil, and plant extracts) follow a log-normal (LN) distribution to a very high degree of correlation.

Achievement of energy focus for distance-of-flight mass spectrometry with constant momentum acceleration and an ion mirror.

Distance-of-flight mass spectrometry (DOF-MS) has not yet been implemented, though it has many potential advantages in a variety of applications. Impeding the implementation of DOF-MS is the development of the required array detectors and working out the equivalents to the focusing methods now used in time-of-flight (TOF) mass analyzers. Ideally, a batch of ions composed of a variety of m/z values, despite initial distributions of space and energy, would be spatially focused at their respective flight distances at the same time.

Axial focusing following low kinetic energy pulsed extraction from a miniature linear ion trap.

Using an axial focusing miniature linear ion trap with tubular end cap lenses (MLIT) we have investigated spatial focusing on ion ejection using low kinetic energy pulsed extraction methods. Ion packet widths focused to ca. 1 mm (in both the radial and axial planes) are produced following collisional cooling with helium buffer gas in an MLIT.

Axial ion focusing in a miniature linear ion trap.

A novel miniature linear ion trap with a total length of 19 mm and a quadrupole rod length of 15 mm has been fabricated to enable ion focusing in the axial plane (between the end caps). Each end cap includes an inwardly projecting tubular section, which prevents dc fringe fields from penetrating to the center of the miniature linear ion trap and aids in ion extraction. Axial focusing of ion packets to dimensions of less than 1 mm through collisional cooling is predicted and demonstrated in the miniature linear ion trap.