Simultaneous Mass Analysis Research Articles

Structural Analysis of Intact Monoclonal Antibodies by Electron Transfer Dissociation Mass Spectrometry

Improving qualitative and quantitative characterization of monoclonal antibodies is essential, because of their increasing popularity as therapeutic drug targets. Electron transfer dissociation (ETD)-based top-down mass spectrometry (MS) is the method of choice for in-depth characterization of post-translationally modified large peptides, small- and medium-sized proteins, and noncovalent protein complexes. Here, we describe the performance of ETD-based top-down mass spectrometry for structural analysis of intact 150 kDa monoclonal antibodies, immunoglobulins G (IgGs). Simultaneous mass analysis of intact IgGs as well as a complex mixture of ETD product ions at sufficiently high resolution and mass accuracy in a wide m/z range became possible because of recent advances in state-of-the-art time-of-flight (TOF) mass spectrometry. High-resolution ETD TOF MS performed on IgG1-kappa from murine myeloma cells and human anti-Rhesus D IgG1 resulted in extensive sequence coverage of both light and heavy chains of IgGs and revealed information on their variable domains. Results are superior and complementary to those previously generated by collision-induced dissociation. However, numerous disulfide bonds drastically reduce the efficiency of top-down ETD fragmentation within the protected sequence regions, leaving glycosylation uncharacterized. Further increases in the experiment sensitivity and improvement of ion activation before and after ETD reaction are needed to target S-S bond-protected sequence regions and post-translational modifications.

Simultaneous Mass Analysis of Positive and Negative Ions Using a Dual-Polarity Time-of-Flight Mass Spectrometer

Positive and negative ions produced from matrix-assisted laser desorption/ionization (MALDI) were simultaneously measured using a newly developed dual-polarity time-of-flight mass spectrometer. This instrument is effective not only for express and comprehensive mass analysis but also for studying the ionization mechanisms of biomolecules. It comprises two identical time-of-flight mass analyzers located symmetrically about a MALDI ion source. The ion optics are arranged to be able to extract positive and negative ions synchronously with equal efficiency to each corresponding mass analyzer. Mass spectra of various proteins with molecular weights as large as that of myoglobin monomer and dimer were obtained. The spectral patterns obtained in this work are approximately mirror images with opposite polarities.

Si-rich surface layer of photochemically deposited silicon nitride

The etching reaction of a photochemically deposited silicon nitride film with F2 has been observed in situ using polarization-modulation infrared spectroscopy and quadruple mass spectrometry. The infrared spectrum of the silicon nitride film before etching exhibited two bands at 1030 and 975 cm−1, arising from Si-N vibration. Exposure of the film at 423 K to F2 led to an intensity decrease of the lower-frequency band, while the higher-frequency band increased. Simultaneous mass analysis revealed that the etching products evolved into the gas phase were SiF4 and H2. However, a further admission of F2 resulted in a slight decrease in intensity of the 975 cm−1 band as well as a slight evolution of SiF4. These results strongly suggest the presence of a metastable Si-rich layer on the surface of the silicon nitride film prior to reaction with F2. Infrared measurements have also been made in the Si-H stretching region, the results of which are described and discussed.

Mobility and longitudinal diffusion of SF5-and SF6- in SF6

The drift and longitudinal diffusion of SF5- and SF6- in SF6 has been studied with a drift-tube mass spectrometer. Values of the reduced mobility and of the density-normalized longitudinal diffusion coefficient of these ions are reported over the combined E/N range 15-460 Td. The present zero-field reduced mobilities for both ions are in excellent agreement with those of Patterson (1972). To the authors' knowledge, the present data are the first measured with simultaneous mass analysis over the entire E/N range.

Neutral-fragment mass spectra of the tetramethyl compounds of the group IV a elements

A neutral-fragment mass spectrometer capable of simultaneous mass analysis of positive ions and neutral fragments resulting from interactions of electrons and molecules has been used to characterize the unimolecular decompositions of the tetramethyl derivatives of C, Si, Ge, Sn, and Pb. Four different kinds of neutral species have been observed, the most abundant being excited M(CH 3) 4 *. Methyl radicals produced from these compounds by dissociative ionization are vibrationally excited in a state corresponding to the first symmetrical stretch. Atomic ions, Ge +, Sn +, and Pb +, are formed by dissociative ionization and from an autoionizing state.