MALDI-TOF MS analysis was conducted on ultrafleXtreme mass spectrometer (Bruker) in linear mode, equipped with 355 nm Nd:YAG laser. The signal was accumulated in 50000 shots; the intensity of the laser beam was the same in all experiments. MS instrument calibration was done with BSA (Sigma-Aldrich, 66431 Da), Insulin (Sigma-Aldrich, 5733.49 Da), Myoglobin (Sigma-Aldrich, 16952.30 Da) proteins in CHCA matrix. A groundsteel target was used.