The data used for the experiments are available in CSV files. As many control measurements were carried out, there are often more data in the files than was used for analysis. Each file contains a calibration, as well as blank and unknown sample measurements. The data were measured using a Vanquish HPLC Flex system with a binary pump, coupled to an Orbitrap Q-Exactive mass spectrometer (both from Thermo Fisher Scientific). Evaluation was performed using the ‘QuanBrowser’ software (Thermo Xcalibur 4.2.47, Thermo Fisher Scientific).