Takaya Satoh

Structural Analysis of Triacylglycerols by Using a MALDI-TOF/TOF System with Monoisotopic Precursor Selection

AbstractA new MALDI-TOF/TOF system with monoisotopic precursor selection was applied to the analysis of triacylglycerols in an olive oil sample. Monoisotopic precursor selection made it possible to obtain product-ion mass spectra without interference from species that differed by a single double bond. Complete structure determination of all triacylglycerols, including structural isomers, was made possible by interpreting the charge-remote fragmentation resulting from high-energy collision-induced dissociation (CID) of the sodiated triacylglycerols.

Detailed Structural Analysis of Lipids Directly on Tissue Specimens Using a MALDI-SpiralTOF-Reflectron TOF Mass Spectrometer

Direct tissue analysis using a novel tandem time-of-flight (TOF-TOF) mass spectrometer is described. This system consists of a matrix-assisted laser desorption/ionization ion source, a spiral ion trajectory TOF mass spectrometer “SpiralTOF (STOF)”, a collision cell, and an offset parabolic reflectron (RTOF). The features of this system are high precursor ion selectivity due to a 17-m flight path length in STOF and elimination of post-source decay (PSD) ions. The acceleration energy is 20 keV, so that high-energy collision-induced dissociation (HE-CID) is possible. Elimination of PSD ions allows observation of the product ions inherent to the HE-CID process. By using this tandem TOF instrument, the product ion spectrum of lipids provided detailed structural information of fatty acid residues.

Mass Spectrometry Imaging and Structural Analysis of Lipids Directly on Tissue Specimens by Using a Spiral Orbit Type Tandem Time-of-Flight Mass Spectrometer, SpiralTOF-TOF

In this paper, we report the use of mass spectrometry imaging and structural analysis of lipids directly on a tissue specimen, carried out by means of matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry, using a combination of spiral orbit-type and reflectron-type time-of-flight mass spectrometers. The most intense peak observed in the mass spectrum from a brain tissue specimen was confirmed as phosphatidylcholine (34 : 1) [M+K](+), using tandem mass spectrometry. The charge remote fragmentation channels, which are characteristically observed using high-energy collision-induced dissociation, contributed significantly to this confirmation. Accurate mass analysis was further facilitated by mass correction using the confirmed peak. In mass spectrometry imaging, the high resolving power of our system could separate doublet peak of less than 0.1 u difference, which would otherwise be problematic when using a low-resolution reflectron type time-of-flight mass spectrometer. Two compounds, observed at m/z 848.56 and 848.65, were found to be located in complementary positions on a brain tissue specimen. These results demonstrate the importance of a high-performance tandem time-of-flight mass spectrometer for mass spectrometry imaging and analysis of observed compounds, to allow distinction between biological molecules.

Separation of Isobaric Compounds Using a Spiral Orbit Type Time-of-Flight Mass Spectrometer, MALDI-SpiralTOF.

The development of a MALDI-TOF mass spectrometer that utilizes spiral ion trajectory, SpiralTOF, is reported. The total flight path length was 17 m, which is five times longer than that in commonly used reflectron ion optical system. The SpiralTOF reduced the dependence of the mass resolving power on the mass of the analyte, while improving the accuracy of the mass measurements. Furthermore, SpiralTOF has two advantages that can be exploited for the separation of minor abundant isobaric components in mass spectra. One is the reduction in chemical background due to the post source decay (PSD), which is achieved through PSD ion elimination by electrostatic sectors contained within the SpiralTOF. The other is that the stabilities of peak positions are improved during mass spectrum accumulation. The peak drift caused by the fine structure of matrix crystals and the small irregularities on the sample surface can be reduced by extending the flight path. In this study, these advantages are demonstrated via the analysis of a block copolymer and mass spectrometry imaging (MSI) of lipids.

Matrix-Assisted Laser Desorption/Ionization

Matrix-assisted laser desorption/ionization (MALDI) is a “soft” ionization technique commonly used in mass spectrometry (Fig. 60.1). It uses organic compounds (typically an organic acid) called “matrix” as a means of facilitating desorption and ionization efficiency.

Matrix-Assisted Laser Desorption Ionization Imaging Mass Spectrometry of Drug Distribution in Mouse Brain Tissue by High-Resolution Time-of-Flight Mass Spectrometry

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry provides the opportunity to visualize the distributions of drugs and metabolites in tissue specimens without requiring radioisotopes, as are used for whole-body autoradiography. However, the analysis of low-molecular-weight compounds is often difficult using the common reflectron-type MALDI time-of-flight mass spectrometers. Insufficient mass resolving power causes overlapping of the target drug peak with matrix compound or surface contaminant peaks. To solve this issue, we describe the procedure for imaging mass spectrometry using a high-mass-resolution mass spectrometer that can separate isobaric peaks.

Effects of molecular weight and cationization agent on the sensitivity of Bi cluster secondary ion mass spectrometry: Effects on the sensitivity of Bi cluster SIMS

RATIONALE Bi cluster secondary ion mass spectrometry (SIMS) is one of the most promising tools for precise analysis of synthetic polymers. However, the sensitivity in the high-mass region is still insufficient compared with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Accordingly, the effects of metal assistance (cationization agents) were investigated in this study. METHODS To investigate the effects caused by varying the ionization agent, three different polyethylene glycol (PEG) samples were prepared, one with an Ag-deposited film, and two others mixed with Ag and Na, respectively. The measurements were performed by using a commercial Bi cluster SIMS and MALDI-TOFMS systems. The mass spectrum obtained with MALDI-TOFMS was used as a reference molecular weight distribution to evaluate the effects of molecular weight and primary ion species (Bi+ , Bi3+ , Bi32+ ) on the sensitivity of Bi cluster SIMS. RESULTS The intensity of each secondary ion was the highest in Bi32+ irradiation, and the lowest in Bi+ irradiation. Regarding the cationization agents, the secondary ion yield was the highest for the sample mixed with Ag, while the degree of decay of sensitivity along with the increase in molecular weight was the smallest for the sample mixed with Na. CONCLUSIONS It was suggested that the cationization mechanism consists of pre-formed ionization and gas-phase ionization processes. The sensitivity of Bi cluster SIMS decreases to approximately one-fiftieth in every 1000 u. These results might help in understanding the mechanism of cationization and further enhancement of secondary ion yields of polymers. Copyright

MALDI and LDI Imaging of Forensic Samples by Using A Spiral-Trajectory Ion Optics Time-of-Flight Mass Spectrometer

Recently, matrix-assisted laser desorption/ionization (MALDI) imaging techniques have been developed for biological sciences to evaluate and understand the distribution of various chemicals on biological surfaces. In particular, this technique provides useful visual information about the locations of specific chemicals on surfaces. In this work, we explored the use of MALDI imaging for forensically relevant samples that included gunshot residue (GSR), fingerprints and ballpoint ink. These measurements were done using a spiraltrajectory ion optics time-of-flight mass spectrometer (SpiralTOF-MS [1]). This TOF system has a unique 17m flight path that provides ultrahigh-resolution mass spectra over a wide m/z range, even if the sample is not perfectly flat. Additionally, the m/z axis is very stable over the long measurement times required for MALDI imaging. GSR samples were obtained on an electrically conductive adhesive that was pressed against the back of a shooter’s hand after a handgun was discharged. The fingerprint samples were collected on electrically conductive ITO glass slides from both a smoker and a non-smoker. The smoker’s fingerprint was collected immediately after smoking a cigarette. 2,5-dihydroxybenzoic acid (DHB) was used as the MALDI matrix. This matrix was dissolved in methanol at a fixed concentration of 30 mg/mL. 1-2 mL of DHB solution was sprayed on each sample surface by using a commercial airbrush. Samples were then analyzed by using a high-resolution MALDI-TOFMS instrument. A polypropylene glycol (PPG) mixture of average MW 425 and 1000 were used as an external exact-mass reference standard. The GSR sample surface was analyzed for inorganic element distributions. As a starting point, we

Imaging Mass Spectrometry Using Ultra-high Mass Resolution Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometer, SpiralTOF

Imaging mass spectrometry (IMS) has been used for biological applications, to assess the distribution of proteins, peptides, lipids, drugs, and their metabolites in a tissue specimen. IMS has expanded during the last decade using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, which adopted a linear and a reflectron ion optical systems. A reflectron MALDI-TOF mass spectrometer, using a delayed extraction technique, has higher mass resolution than linear MALDI-TOF mass spectrometer. However, its high mass resolution is available only within limited mass range, which isn’t sufficient for analysis in low-molecular compounds such as lipids, drugs and drug metabolites. It is necessary to extend flight path length to improve mass resolution and mass accuracy in wide mass range. However, the flight path length of a reflectron TOF mass spectrometer is limited by its instrument size, and is difficult to be extended beyond certain length restricted by the instrument dimension. We developed a MALDI-TOF mass spectrometer with a spiral ion trajectory, SpiralTOF[1], to solve the issue. It has 17 m flight path length within a cubic vacuum housing of approximately 0.6m x 0.6m x 0.7m.