This thesis presents the first isotope-shift measurement of bound-electron g-factors of highly charged ions and determines the most precise value of the electron mass in atomic mass units, which exceeds the value in the literature by a factor of 13. As the lightest fundamental massive particle, the electron is one of natures few central building blocks. A precise knowledge of its intrinsic properties, such as its mass, is mandatory for the most accurate tests in physics - the Quantum Electrodynamics tests that describe one of the four established fundamental interactions in the universe. The underlying measurement principle combines a high-precision measurement of the Larmor-to-cyclotron frequency ratio on a single hydrogen-like carbon ion studied in a Penning trap with very accurate calculations of the so-called bound-electron g-factor. For the isotope-shift measurement, the bound-electron g-factors of two lithium-like calcium isotopes have been measured with relative uncertainties of a few 10^{-10}, constituting an as yet unrivaled level of precision for lithium-like ions. 

2005-2011: Study of physics in Göttingen with stopovers at CERN and the University Claude Bernard Lyon 1. 2011: Diploma in high-energy physics, title: "Performance Study of a Diamond Pixel Detector Prototype for Future ATLAS Upgrades."
2011: Scientist at the Max Planck Institute for Dynamics and Self-Organization, topic: Installation of an experimental setup for the analysis of high turbulences.
2011-2015: PhD student at the GSI Helmholtz Centre for Heavy Ion Research. Since 2015 postdoc at the Max Planck Institute for Nuclear Physics, topic: Installation of a new experimental setup for the most precise determination of the atomic proton and neutron mass.

Introduction.- The g-Factor - Exploring Atomic Structure and Fundamental Constants.- Penning Trap Physics.- Towards the Measurement of the Larmor-to-cyclotron Frequency Ratio.- Determination of the Atomic Mass of the Electron.- Outlook - A New Generation of High-Precision Penning Trap.