High throughput LC-MS is an increasing topic in analytical chemistry. Especially the idle time of a mass spectrometer should be reduced to use these devices more efficiently and save costs. Therefore, the first section of this thesis demonstrated how a dual ion source could be constructed. This ion source was designed to operate the typical ionization modes of LC-MS analyses, ESI, and APCI simultaneously and individually. Direct infusion experiments of reserpine and caffeine indicated that it is possible to run the two ion sources simultaneously. Furthermore, it was shown that switching between the two ion sources does not lead to instabilities in the ion current of the mass spectrometer. A six-port valve was used to couple a HPLC to the dual ion source for the initial chromatographic studies. Switching experiments were performed with cortisol and ß-estradiol, resulting in a minimum switching time between the two probes of 6 s. Repeatability was investigated to be 0.28% intraday and 1.5% interday for APCI and 2.2% intraday and 2.8% interday for ESI. The limit of detection for the standard substances testosterone (ESI), vitamin D₃ (APCI), and 25-hydroxyvitamin D₃ (ESI) was 30 ng L^-1 for testosterone and vitamin D₃ and one µg L^-1 for 25-hydroxyvitamin D₃. The dual ion source was coupled to two HPLCs, making it possible to shorten the idle time of the mass spectrometer and to use individual methods for the two HPLCs. With this technique, the LOD of vitamin D₃ could be reduced to 300 ng L^-1. The final experiment for multiple switching between ESI and APCI and the two UHPLCs shows good repeatability of the peak areas with standard deviations of 1.5% for testosterone and 3.8% for vitamin D₃. In five runs, 50 analyses could be performed, requiring 1.5 min run time for one sample. Therefore, the dual ion source is well suited for the coupling of multiple HPLCs, accompanied by a low analysis time and a low idle time of the mass spectrometer.

The second part of this thesis dealt with developing an argon inverse-low-temperature-plasma (iLTP) ion source for LC tandem MS analysis. With flow rates up to 1000 µL min^-1. The iLTP ion source consists of a modified APCI ion source in which the iLTP probe replaced the APCI needle. This iLTP probe consists of a dielectric quartz tube, a tapered needle-shaped inner electrode made of stainless steel, and a silver ground electrode attached to the outside of the quartz tube. Optical emission spectroscopy was performed using a CCD camera to gain insight into the reactive species produced by the argon iLTP. These species are mainly hydroxyl radicals and metastable argon species (corresponding energies of 11.53 eV and 11.72 eV) that could serve as precursors for an ionization pathway such as metastable helium in helium LTP or via Penning ionization. Infusion experiments indicate a gentle ionization by iLTP, e.g., caffeine, testosterone, reserpine, vitamin D₃, and 25‑hydroxyvitamin D₃, which resulted in the corresponding protonated molecular cations. The concentration dependence of the argon iLTP was demonstrated. Coupling with a UHPLC shows satisfactory inter-day repeatability (n=10) of the analytes with RSD ≤ 5 %. The instrumental detection limit study showed promising results for caffeine, testosterone, reserpine vitamin D₃, and 25‑hydroxyvitamin D₃ of 10 ng L^‑1, 50 ng L^-1, 500 ng L^-1, five µg L^-1, and five µg L^-1, respectively. The Ar-iLTP ion source can be operated with different discharge gases such as helium, nitrogen, synthetic air, or oxygen and lead to specific ionization pathways enabled by different discharge gases. It was demonstrated that an argon iLTP could compete with the helium LTP preferred in the literature. Investigations of pesticide standards and analysis of a forensic toxicology standard with a quantitation limit up to 500 ng L^-1 demonstrate specific fields for applications. The iLTP ion source has comparable LODs to the dual ion source and can compete with the established methods like ESI and APCI.