Andrew W Alexander

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A one-hundred-anode microchannel plate detector is constructed on a 10 cm × 15 cm printed circuit board and attached to a homebuilt matrix assisted laser desorption ionization (MALDI) time-of-flight mass spectrometer. Ringing and cross talk between anodes have been successfully eliminated and preliminary mass spectra of peptide ions recorded. With one(More)
Spontaneous mass and charge losses from individual multi-megadalton ions have been observed with charge detection mass spectrometry (CDMS) by trapping single hepatitis B virus (HBV) capsids for 3 s. Gradual increases in the oscillation frequency of single ions in the ion trap are attributed mainly to mass loss (probably solvent, water, and/or salt). The(More)
Quadrupole mass filters (QMFs) are usually not used to analyze high m/z ions, due to the low frequency resonant circuit that is required to drive them. Here we describe a new approach to generating waveforms for QMFs. Instead of scanning the amplitude of a sine wave to measure the m/z spectrum, the frequency of a trapezoidal wave is digitally scanned. A(More)
An improved directly digital flow controller is evaluated for its ability to modulate gas flow rates. As in the older device, the "GasDAC" (named for its similarity to a weighted-resistor digital-to-analog converter) is capable of controlling gas flow in a linear and reproducible manner with the advantage of having an adjustable range of flow rates. The new(More)
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