Design, Fabrication and Performance Evaluation of a Tandem Time-of-flight Mass Spectrometer

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOFMS) is an important instrument for structural analysis of biological samples through such as post-source-decay (PSD) or collision-induced dissociation (CID) analysis. However, PSD analysis is a relatively low-efficiency method compared with CID analysis.;This project aims to upgrade the TOF instrument to a high performance TOF/TOF instrument. The modification involves (a) the replacement of the two-stage reflectron with a home-built curved-field reflectron (CFR); (b) the fabrication of a high voltage floated collision cell; and (c) the installation of a coaxial microchannel plate (MCP) detector. The CFR and coaxial detector allow simultaneous reflection of precursor ions and all fragment ions. The collision cell provides an effective means of ion activation (CID). In the performance test, precursor ions with almost all the fragment ions were recorded simultaneously in PSD analysis. In CID experiments, the precursor ions were found to undergo fragmentation due to high energy collision with the target gas and by floating the collision cell to high potential (several kV), the mass resolution and signal intensities of low mass fragment ions were improved substantially.;By comparing the performance of curved-field and two-stage reflectron, a hybrid reflectron was proposed, which has adjustable high voltages U1 and U2 on the second and last electrode element, respectively. The electrostatic potential between the second and last electrode element follows curved-field distribution. There are two operation modes for this reflectron: MS and MS/MS mode. Results from theoretical investigation and experiments showed that in MS mode, optimal energy compensation could be achieved through tuning the values of U1 and U2; in MS/MS mode, a full mass scale spectrum as well as spectra segments with high mass resolution within a narrower mass range could be obtained by setting U1 and U2 with appropriate values. These results indicated that the hybrid reflectron had the advantages both of curved-field reflectron and two-stage reflectron.