Development of multiplexed ion trap mass spectrometers for high-throughput analysis

Amy Marie Gilchriest Tabert, Purdue University


Two fully-multiplexed ion trap mass spectrometers were developed for high-throughput analysis. Each novel instrument features four parallel ion source/mass analyzer/detector channels assembled in a single vacuum chamber and operated using a common set of control electronics. The first instrument utilized an array of miniature cylindrical ion traps (CITs) coupled to an array of electron ionization/chemical ionization (EI/CI) sources and an array of miniature channeltron electron multipliers. On a separate platform with a vacuum chamber designed to minimize neutral cross-talk between adjacent channels, a multi-channel EI rectilinear ion trap (RIT) mass spectrometer was constructed. As the CIT is a geometrically simple substitute for the hyperbolic Paul ion trap, the RIT mass analyzer employed is a simplified alternative to the linear ion trap. Both instruments are characterized in terms of mass resolution (peak width <0.3 m/z at half maximum), mass/charge range (up to m/z 500), and cross-talk. Using the multiplexed CIT mass spectrometer, a novel experiment is performed for improved specificity in the analysis of a single sample by simultaneous measurements made with multiple methods of ionization, including EI and methane CI, in parallel channels of the instrument. Using the multiplexed RIT mass spectrometer, less than ∼5% cross-talk is evident between adjacent channels, and mass spectra are successfully acquired from four unique samples simultaneously. An account is given of the evaluation of the ion trap mass analyzers in the RIT instrument, and a novel diagnostic method involving co-occurrence of boundary and resonance ejection in a single mass scan was discovered. Excellent mass range linearity and nearly identical mass calibration between the RITs allow the use of tandem mass spectrometry in all parallel channels. Simultaneous MS/MS is demonstrated using four compounds (isomers and isobars) with the same nominal m/z ratio of the molecular radical cation and distinctive fragmentation patterns. Pre-acquisition differential data is obtained by real-time, point-by-point subtraction of the ion signals from two channels, offering proof-of-principal for comparison of mass spectra in high-throughput screening applications while reducing data storage requirements.




Cooks, Purdue University.

Subject Area

Analytical chemistry

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