Q exactive hf orbital trapping mass spectrometer

MSI measurements were carried out on an AP-SMALDI5 AF ion source (TransMIT GmbH, Giessen, Germany) coupled to a ‘Q Exactive HF’ orbital trapping mass spectrometer (Thermo Fisher Scientific GmbH, Bremen, Germany) and alternatively on a home-built ultra-high-resolution AP-MALDI MSI source, coupled to a ‘Q Exactive’ orbital trapping mass spectrometer (Thermo Fisher Scientific GmbH, Bremen, Germany). Laser fluence was adjusted by controllable dichroic filters. The highest available mass resolution of 240,000 or 140,000 was used for all experiments on the Q Exactive HF or Q Exactive, respectively. A fixed injection time of 500 ms was set on both devices and a high voltage of 4 kV was applied to the samples. Laser energy was adjusted individually for each experiment.

The wheat seed sections imaging experiments were acquired using a high-spatial-resolution (≥5 µm step size) atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization MSI ion source (AP-SMALDI5 AF, TransMIT GmbH, Giessen, Germany) coupled to a Q Exactive HF orbital trapping mass spectrometer (Thermo Fisher Scientific GmbH, Bremen, Germany).
The minimum laser beam focus results in an ablation spot diameter of 5 μm [26 (link),52 (link)]. For the experiments described below, laser step sizes pf at 15 and 20 μm, respectively, were set. The mass spectrometer was operated in positive-ion mode: scan range m/z 250–1000; spray voltage +3 kV; capillary temperature 250 °C, automatic gain control (AGC) disabled; cycle time 1.3 pixels/s. The internal mass calibration was performed using known matrix ion signals as lock mass values (m/z 716.12461), providing a mass accuracy of better than 2 ppm root mean square error over the entire measurement.

Plant tissue sections imaging experiments were performed using a high spatial resolution (≥ 5 μm step size) atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization ion source (AP-SMALDI5 AF, TransMIT GmbH, Giessen, Germany) coupled to a Q Exactive HF orbital trapping mass spectrometer (Thermo Fisher Scientific GmbH, Bremen, Germany). The minimum laser beam focus results in an ablation spot diameter of 5 μm (Römpp and Spengler, 2013 (link)). For the experiments described below, a laser step size of 7–20 μm was set, depending on the plant organ under investigation. The mass spectrometer was operated in positive-ion mode. The following parameters were set: scan range m/z 250–1000; spray voltage + 3 kV; capillary temperature 250°C, automatic gain control (AGC) was disabled; cycle time for one pixel 1 s. Internal mass calibration was performed using known matrix ion signals as lock mass values (m/z 716.12461), providing a mass accuracy of better than 2 ppm root mean square error over the entire measurement.