MALDI-ToF MS was performed on a Bruker Autoflex maX instrument equipped with a 355 nm solid-state laser in the reflectron and linear mode and 20 kV acceleration voltage. The samples were prepared according to the dried droplet method. Therefore, matrix (trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB), 10 g L -1 in THF), analyte (10 g L -1 in THF) and salt (silver trifluoroacetate, 10 g L -1 ) were dissolved and mixed in the ratio of 20 : 5 : 1 and 0.5 µL of the mixture was placed and dried on the target plate.