Further development and application of a mobile multiple-reflection time-of-flight mass spectrometer for analytical high-resolution tandem mass spectrometry
In this work, a mobile multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) for analytical mass spectrometry was enhanced in many important aspects. Technical as well as software-based improvements have been added to the instrument, thus greatly increasing its performance and applicability. Changes have been applied to the whole beam preparation system of the MR-TOF-MS. In this context, the electronic setup was completely overhauled and a quadrupole mass filter was commissioned. Collision-induced dissociation and a new trigger system have been implemented, enabling the possibility to perform sophisticated tandem mass measurements. Additional modifications have been done to the ion-optics and detector system of the time-of-flight analyzer to improve the instrument´s resolving power and sensitivity.An average mass accuracy of 0.3 ppm was achieved in measurements with several isotopes of the molecules hexamethoxyphosphazene and caffeine. With a flight time of about 6 ms, mass resolving powers of 200,000 could be obtained. The amino acid arginine was utilized to probe the instrument´s linear dynamic range, which was found to cover 5 orders of magnitude in analyte concentration.Space charge effects in the analyzer were extensively investigated. Corresponding simulations and measurements are in excellent agreement with each other. Several approaches such as the change of the position of intermediate time-focus and the use of high extraction field strengths seem to be very promising solutions and will be able to reduce space charge effects in future measurements.It was shown that the method of mass-selective re-trapping is ideally suited to perform tandem mass measurements with high-resolution mass separation in every stage of the measurement. Resolving powers as well as efficiencies of re-trapping were studied in detail and separation powers of up to 70,000 have been obtained. Measurements with the two amino acids glutamine and lysine (mass difference of 36.4 mu) were conducted to illustrate the MS/MS and MSn capabilities of the instrument. Additionally, a crude oil sample has been analyzed in a first proof-of-principle application. There, a specific compound could be successfully isolated from its isobaric contaminants and the corresponding fragment spectrum has been recorded.
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