The Seven S Criteria for Evaluating the Performance of a MALDI Mass Spectrometer for MSI.

Our goal in this work is to evaluate a new combination linear/reflector MALDI-TOF instrument toward satisfying all "7S criteria" for the ideal MSI mass spectrometer. The linear analyzer satisfies all of the 7 criteria except for Specificity. The new instrument described here adds a reflector to provide up to 50,000 mass resolving power with ppm mass accuracy and with no sacrifice in speed, spatial resolution, and sensitivity demonstrated earlier for the linear MALDI-TOF.

Analysis and Quantitation of Glycated Hemoglobin by Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry.

Measurement of glycated hemoglobin is widely used for the diagnosis and monitoring of diabetes mellitus. Matrix assisted laser desorption/ionization (MALDI) time of flight (TOF) mass spectrometry (MS) analysis of patient samples is used to demonstrate a method for quantitation of total glycation on the β-subunit of hemoglobin. The approach is accurate and calibrated with commercially available reference materials.

Tissue protein imaging at 1 μm laser spot diameter for high spatial resolution and high imaging speed using transmission geometry MALDI TOF MS.

We have achieved protein imaging mass spectrometry capabilities at sub-cellular spatial resolution and at high acquisition speed by integrating a transmission geometry ion source with time of flight mass spectrometry. The transmission geometry principle allowed us to achieve a 1-μm laser spot diameter on target. A minimal raster step size of the instrument was 2.

The future of biological mass spectrometry.

Biological applications of mass spectrometry have grown exponentially since the discovery of MALDI and electrospray ionization techniques. This growth has been further fueled by the massive volume of DNA sequence information that is now available. An ambitious goal of some of this research is to monitor the level and modification of all proteins and metabolites in a biological sample such as plasma.

Novel three-dimensional MALDI plate for interfacing high-capacity LC separations with MALDI-TOF.

Novel matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) sample plates employing collimated-hole structures have been developed that allow capture and concentration of samples while simultaneously acting as a sink for carrier solvents. These plates were designed to provide an efficient interface between higher-capacity liquid chromatography (LC) separations and MALDI-TOF mass spectrometry (MS). LC-MALDI using conventional plates can accommodate the low-flow (< 1 microL/min) separation protocols typically used in on-line LC-MS methods, and can also be used with higher flow rate, larger columns, but are ultimately limited by the capacity of the two-dimensional surface onto which the sample is deposited.

Modern MALDI time-of-flight mass spectrometry.

This paper focuses on development of time-of-flight (TOF) mass spectrometry in response to the invention of matrix-assisted laser desorption/ionization (MALDI). Before this breakthrough ionization technique for nonvolatile molecules, TOF was generally considered as a useful tool for exotic studies of ion properties but was not widely applied to analytical problems. Improved TOF instruments and software that allow the full potential power of MALDI to be applied to difficult biological applications are described.

Fragmentation of leucine enkephalin as a function of laser fluence in a MALDI TOF-TOF.

The effects of laser fluence on ion formation in MALDI were studied using a tandem TOF mass spectrometer with a Nd-YAG laser and alpha-cyano hydrocinnamic acid matrix. Leucine enkephalin ionization and fragmentation were followed as a function of laser fluence ranging from the threshold of ion formation to the maximum available, that is, about 280-930 mJ/mm2. The most notable finding was the appearance of immonium ions at fluence values close to threshold, increasing rapidly and then tapering in intensity with the appearance of typical backbone fragment ions.

Bacillus cereus strains fall into two clusters (one closely and one more distantly related) to Bacillus anthracis according to amino acid substitutions in small acid-soluble proteins as determined by tandem mass spectrometry.

Small acid-soluble proteins (SASPs) are located in the core region of Bacillus spores and have been previously demonstrated as reliable biomarkers for differentiating Bacillus anthracis and Bacillus cereus. Using MS and MS-MS analysis of SASPs further phylogenetic correlations among B. anthracis and B.

Tandem time-of-flight mass spectrometry.

A new tandem time-of-flight (TOF-TOF) instrument has been developed by modifying a standard matrix-assisted laser desorption ionization (MALDI)-TOF instrument to make high-performance, high-energy collision-induced dissociation (CID) MALDI tandem mass spectrometry (MS) a practical reality. To optimize fragment spectra quality, the selected precursor ion is decelerated before entering a floating collision cell and the potential difference between the source and the collision cell defines the collision energy of the ions. Standard operating conditions for tandem MS use a 1-kV collision energy with single-collision conditions and increased laser power for ion formation.

Off-line coupling of high-resolution capillary electrophoresis to MALDI-TOF and TOF/TOF MS.

High-resolution capillary electrophoresis has been coupled to MALDI-TOF and TOF/TOF MS through off-line vacuum deposition onto standard stainless steel MALDI targets. This off-line approach allowed the decoupling of the separation from the MS analysis, thus allowing each to be independently optimized in terms of time. Using BSA tryptic digest as a model sample, the deposited streaks, roughly 100-microm wide, were first analyzed in the MS mode, consuming only a fraction of the sample.

The identification of protein-protein interactions of the nuclear pore complex of Saccharomyces cerevisiae using high throughput matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry.

Mass spectrometry has become the technology of choice for detailed identification of proteins in complex mixtures. Although electrophoretic separation, proteolytic digestion, mass spectrometric analysis of unseparated digests, and database searching have become standard methods in widespread use, peptide sequence information obtained by collision-induced dissociation and tandem mass spectrometry is required to establish the most comprehensive and reliable results. Most tandem mass spectrometers in current use employ electrospray ionization.

De novo sequencing of peptides using MALDI/TOF-TOF.

The recently developed MALDI TOF-TOF instrument yields relatively complex but interpretable fragmentation spectra. When coupled with a straightforward sequence extension algorithm, it is possible to develop complete peptide sequences de novo from the spectra. This approach has been applied to a set of peptides derived from typtic digestion of electrophoretically separated sea urchin egg membrane proteins.

Matrix-assisted laser desorption/ionization-tandem mass spectrometry with high resolution and sensitivity for identification and characterization of proteins.

Although peptide mass fingerprinting is currently the method of choice to identify proteins, the number of proteins available in databases is increasing constantly, and hence, the advantage of having sequence data on a selected peptide, in order to increase the effectiveness of database searching, is more crucial. Until recently, the ability to identify proteins based on the peptide sequence was essentially limited to the use of electrospray ionization tandem mass spectrometry (MS) methods. The recent development of new instruments with matrix-assisted laser desorption/ionization (MALDI) sources and true tandem mass spectrometry (MS/MS) capabilities creates the capacity to obtain high quality tandem mass spectra of peptides.