High-energy collision-induced dissociation of phosphopeptides using a multi-turn tandem time-of-flight mass spectrometer ‘MULTUM-TOF/TOF’

✍ Scribed by Shuichi Shimma; Hirofumi Nagao; Anastassios E. Giannakopulos; Shigeo Hayakawa; Kunio Awazu; Michisato Toyoda

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 418 KB
• Volume: 43
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.1352

✦ Synopsis

High-energy collision-induced dissociation of phosphopeptides using a multi-turn tandem time-of-flight mass spectrometer 'MULTUM-TOF/TOF' A multi-turn tandem time-of-flight mass spectrometer (MULTUM-TOF/TOF) has been designed and constructed at Osaka University. 1,2 The MULTUM-TOF/TOF consists of a matrix-assisted laser desorption/ionization (MALDI) ion source, a multi-turn TOF mass spectrometer (MULTUM) 3 -9 as MS1, a collision cell and a quadraticfield ion mirror 10 as MS2. The MULTUM-can overcome the problem of precursor ion selection in TOF by increasing the number of cycles. Quadratic-field ion mirrors inherently achieve time focusing, independent of kinetic energies of product ions. That means the quadratic-field ion mirror can focus simultaneously all the product ions which have different kinetic energies. It is unnecessary to raise the potential of the collision cell in order to reduce the energy variation of product ions. Therefore, ions accelerated in the ion source can enter the collision cell without deceleration, namely high-energy collision-induced dissociation (CID) is available. In this study, an insight on possible uses of the high-energy collision capabilities of our instrument, and its applicability on the detection of labile modifications, such as phosphorylation are presented.

Phosphopeptide (YGGMHRQE(pT)VDC) was synthesized using an automated peptide synthesizer (PSSM-8, Shimadzu, Kyoto, Japan) with the method published by Wakamiya et al. 11 In this work, a liquid matrix reported by Kumar Kolli et al. was used. 12 The matrix solution was prepared by dissolving 35 mg of 3-aminoquinoline (Sigma-Aldrich, St. Louis, MO) in 150 µl of a saturated ˛-cyano-4hydroxy cinnamic acid (˛-CHCA) solution. The solvent of ˛-CHCA was 100% methanol. The matrix solution was then mixed in a ratio of 1 : 1, with the phosphopeptide (50 pmol/µl) solution dissolved in 0.1% trifluoroacetic acid.

Detailed descriptions of MULTUM-TOF/TOF have been presented in a previous publication. 1 A schematic drawing of MULTUM-TOF/TOF is shown in Fig. 1(a). On the left part of the figure, the MALDI ion source is shown. The ions are produced using a nitrogen laser operating at repetition rates of 10 Hz. The middle part of the figure is the MULTUM. The ion optical properties of the design maintain constant width of the ion packet while the total flight length increases. The same image focused in space and in time is repeated at every cycle (1.308 m/cycle) of the ion packet. Therefore, distances up to tens or hundreds of meters can be available by changing the number of cycles in the MULTUM part. On the right side of the same figure, the quadratic-field ion mirror is shown. The mirror is composed of 33 electrodes, plus two rear electrodes. The spacing between electrodes was not uniform and the applied potential difference between adjacent electrodes was fixed. The ion gate and collision cell are located between the MULTUM and quadratic-field ion mirror. The ion gate consists of two square parallel plates of 10-mm width with 10-mm spacing. One plate was always kept at ground potential, while the second plate was changed from C1 kV to ground with a pulse duration of 100-300 ns. All mass spectra were obtained in positive ion detection mode at an accelerating voltage of 20 kV. To obtain CID spectra, helium gas was used as a collision gas, and the gas flow rate was adjusted via a needle valve. CID spectra were acquired in two different modes. These distinct operation modes were defined as follows: the first mode was the linear mode (Fig. 1(b)) where the ions passed straight through the MULTUM without prescribing a closed trajectory. The second mode was the multi-turn mode (Fig. 1(c)) where the ions flew in the same orbit of MULTUM part many times. Owing to the short flight distance in the linear mode, all the isotopomers are allowed in the collision cell (Fig. 1(d)). On the other hand, one isotopomer was selected for further CID in the multi-turn mode.