Volume 78, Issue 7, July 2007
Index of content:
High-energy collision induced dissociation fragmentation pathways of peptides, probed using a multiturn tandem time-of-flight mass spectrometer “MULTUM-TOF/TOF”78(2007); http://dx.doi.org/10.1063/1.2751403View Description Hide Description
A new multiturn tandem time-of-flight(TOF)mass spectrometer “MULTUM-TOF/TOF” has been designed and constructed. It consists of a matrix-assisted laser desorption/ionization ion source, a multiturn TOFmass spectrometer, a collision cell, and a quadratic-field ion mirror. The multiturn TOFmass spectrometer can overcome the problem of precursor ion selection in TOF, due to insufficient time separation between two adjacent TOF peaks, by increasing the number of cycles. As a result, the total TOF increases with the increase in resolving power. The quadratic-field ion mirror allows temporal focusing for fragment ions with different kinetic energies. Product ion spectra from monoisotopically selected precursor ions of angiotensin I, substance P, and bradykinin have been obtained. The fragment ions observed are mainly the result of high-energy collision induced dissociation.
78(2007); http://dx.doi.org/10.1063/1.2751100View Description Hide Description
A new cylindrical ion cyclotron resonancecell with electrodes of different diameters is characterized. It consists of a central segmented electrode for ion trapping and detection and two planar trappingelectrodes with a center bore, to which two small tube electrodes are fitted. The cell can trap either positive or negative ions or both ion polarities in the center region. For trapping both ion polarities, an unsymmetrical double well potential can be generated. Ions generated from by electron impact or electron attachment are investigated. In depth analysis of radial excitation patterns of positive and negative ions trapped simultaneously in different stability regions reveals sharp discrimination in the extent of radial acceleration. SIMION simulations of the radial excitation show different trajectories of positive and negative ions. Axial component of radial dipolar excitation field exists in the terminal stability regions.
New frequency/voltage converters for ac-electrogravimetric measurements based on fast quartz crystal microbalance78(2007); http://dx.doi.org/10.1063/1.2751093View Description Hide Description
A better understanding of the mechanisms located at the solid/electrolyte interface is becoming essential to the development of new applications in the electrochemical fields. The fast quartz crystal microbalance is an attractive and powerful gravimetric sensor which can be used in the dynamic regime to determine a mass/potential transfer function. The principle is equivalent to classical electrochemical impedance measurements; the only difference is the determination of mass changes given by the quartz crystal microbalance rather than current changes following sine wave modulations of the applied potential. This function appears very well adapted to characterize ionic exchanges at the electrochemicalinterface. Frequency/voltage converters are the key devices in translating the microbalance frequency response in terms of a continuous voltage change. The latter allows the transfer function to be obtained via a frequency response analyzer. Different converters were tested in this work in order to improve the performances of the experimental setup.
Measuring solid-state quantum yields: The conversion of a frequency-doubled Nd:YAG diode laser pointer module into a viable light source78(2007); http://dx.doi.org/10.1063/1.2757471View Description Hide Description
This article outlines the difficulties associated with measuring quantum yields for solid-state samples using a high-pressuremercury arc lamp as the irradiation source. Details are given for the conversion of an inexpensive frequency-doubled neodymium-doped yttrium aluminum garnet (Nd:YAG)diode laser pointer module into a viable irradiation source. The modified Nd:YAG laser was incorporated into a computer-controlled system, which allowed for the simultaneous irradiation and spectroscopic monitoring of the sample. The data obtained with the Nd:YAGdiode laser system show far less scatter than data obtained with a high-pressureHg arc lamp, and consequently the degradation rates obtained with the laser system could be calculated with far greater accuracy.