Miniaturized time-of-flight mass spectrometer for peptide and oligonucleotide analysis.

A matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer was developed which uses a novel reflectron composed of a grounded cylinder and an adjustable endcap electrode to provide high-order kinetic energy focusing for a miniaturized mass analyzer. The nearly quadratic potential form of the reflecting field focuses ions desorbed from a source of very small dimensions formed by placing the sample probe within the centered hole of the coaxial dual channel plate detector. At the same time, the depth of the reflectron can be adjusted to accommodate a short drift length between the source/detector and the reflectron. For larger drift lengths, in particular to allow the addition of an XY stage for the analysis of sample arrays, endcap reflectron focusing can be combined with time-delayed ion extraction to achieve good mass resolution. The instrument has been used for the analysis of peptides digested with trypsin or carboxypeptidase, and also small DNA oligomers.

High-order kinetic energy focusing in an end cap reflectron time-of-flight mass spectrometer.

A reflectron is described which provides high-order kinetic energy focusing using a simple geometry that does not require a set of resistively coupled lens elements. The reflectron is implemented in an approximately 2.0 in (overall length) mass analyzer as part of an effort to provide highly miniaturized mass spectrometers that may be utilized as field-portable instruments for environmental analysis, biological agent detection, or diagnostics.

Matrix-assisted laser desorption/ionization tandem reflectron time-of-flight mass spectrometry of fullerenes.

Atandem reflectron time-of-flight mass spectrometer developed in our laboratory provides a unique opportunity to investigate the collision-induced dissociation of fullerene ions formed by matrix-assisted laser desorption/ionization (MALDI). Specifically, this opportunity arises from the ability to utilize high energy collisional activation (normally available only on tandem sector instruments by using continuous ionization techniques) for ions formed by pulsed laser desorption, whereas most MALDI time-of-flight instruments record product ion mass spectra of ions formed by metastable or postsource decay. In this study we investigate the products of mass-selected and collisionally activated C 60 (+) and C 70 (+) ions by using different target gases over a range of target gas pressures. In general, heavier target gases produce more extensive fragmentation and improve the mass resolution of lower mass ionic products because a greater portion of these ions are formed by single collisions. Additionally, the tandem time-of-flight instrument utilizes a nonlinear (curved-field) reflectron in the second mass analyzer that enables high energy collision-induced dissociation spectra to be recorded without scanning or stepping the reflectron voltage.

Sequencing peptides without scanning the reflectron: post-source decay with a curved-field reflectron time-of-flight mass spectrometer.

A time-of-flight mass spectrometer has been developed using a reflectron in which the voltages placed on the lens elements correspond to a function describing the arc of a circle. This curved-field reflectron enables acquisition of focused product-ion mass spectra at a single reflectron voltage. In this paper, we present results from this instrument for the amino acid sequencing of several peptides and describe the method of mass calibration.

A curved field reflectron time-of-flight mass spectrometer for the simultaneous focusing of metastable product ions.

The ability to simultaneously focus a wide mass range of metastable fragment ions formed after the initial ionization event in a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer has been made possible by the development of a new type of ion reflector. This coaxially designed time-of-flight instrument employs a modified single stage reflector whose axial voltage gradient rises differentially in order to produce an alignment of energy focal points for product ions. In contrast, product-ion focusing in conventional constant field reflectors occurs over a broad range of distances from the reflectron exit. Approximately 90% of the product-ion mass spectrum can be collected without adjustment, thereby eliminating the need to scan the reflector voltage. Design considerations of the curved field reflectron, its calibration properties and representative metastable spectra of several peptides are discussed.

A curved-field reflectron for improved energy focusing of product ions in time-of-flight mass spectrometry.

A new type of curved-field reflectron has been developed for the energy focusing of ions formed after initial acceleration in time-of-flight (TOF) mass spectrometers. These include ions generated in the dissociation region of a tandem TOF, as well as metastable decay products formed in the field-free drift region prior to their reflection. Unlike conventional linear-field reflectrons, which focus product ions to different focal lengths that are proportional to the mass (energy) of the fragment, the new curved-field reflectron energy focuses all ions to within a small region near the exit of the reflectron. Thus, the collection of resolved fragment peaks is possible without scanning or stepping the potential gradient of the reflectron, enabling faster acquisition of the production spectrum and, more importantly, true multiplex recording of the spectra from each ionization event. Theoretical considerations of the design are discussed along with an evaluation of collision-induced dissociation data, demonstrating the performance of the new reflectron in a tandem TOF instrument.

Tandem time-of-flight mass spectrometer.

A compact, laser desorption tandem time-of-flight mass spectrometer is described. The instrument incorporates two dual-stage reflectron analyzers and a collision region for producing product ions by collision-induced dissociation. Selection of ions of a particular mass is accomplished by deflection of ions from stable trajectory angles entering the second reflectron, while the use of a pulsed valve for introduction of the collision gas obviates the need for differential pumping of the collision region. Initial results are presented, as well as a discussion for optimizing the performance of tandem time-of-flight instruments.

Interactions at the active site of glycogen phosphorylase b. A new laser probe.

The flash excitation of the pyridoxal 5'-phosphate cofactor of glycogen phosphorylase b by an ultraviolet laser produces a transient state from a proton transfer of the bound cofactor. The rate of decay of this transient state is sensitive to the ionization state of the cofactor. This proved a useful probe for the ionization state of the 5'-phosphate group of the cofactor on the binding by the enzyme of various substrates. The decay rate data show, for the binding of glucose 1-phosphate, a partially negative 5'-HPO4- and evidence for a PO4-PO4 interaction. The data is interpreted in terms of a dynamic shift of substrates at the active site.