Detection of Ru potential metallodrug in human urine by MALDI-TOF mass spectrometry: Validation and options to enhance the sensitivity

We studied the possibility of detection of [Ru(eta(5)-C5H5)(PPh3)(2)Cl] (abbreviated by RuCp) complex as a model system for Ru-based metallodrugs in human urine by using matrix-assisted laser desorption/ionization time-of -flight mass spectrometry (MALDI-TOF MS) without previous purification or removal of inorganic salts. Inorganic salts might prevent the detection of RuCp by MALDI-TOF MS, most likely through the increased number and intensity of background/organic matrix signals. This problem might be overcome by the acquisition of matrix -free spectra and the addition of nanoparticles, such as carbon dots, to the urine solution. Our results suggest that RuCp is easily detectable by MALDI-TOF MS in all acquisition conditions, with the CHCA matrix being the best for acquisition in phosphate-containing solutions, whereas in urine, DHB and matrix-free approach demonstrated the highest sensitivity, precision, and reproducibility. The sensitivity of matrix-free MALDI detection of RuCp could be increased by the addition of carbon dots to the urine. Based on theoretical calculations for all matrix/analyte combinations, the model for the interaction of RuCp with carbon dots was established, and higher sensitivity explained.