Matrix-assisted laser desorption/ionization, nanostructure-assisted laser desorption/ionization and carbon nanohorns in the detection of antineoplastic drugs. 1. The cases of irinotecan, sunitinib and 6-alpha-hydroxy paclitaxel

The development of surface-assisted laser desorption/ionization (SALDI) methodologies in mass spectrometry allows, in principle, the development of new analytical approaches to qualitative and quantitative measurements on small molecules. Some of these methods have been applied to characterize two antineoplastic drugs: irinotecan (1) and sunitinib (2), and also 6-a-hydroxy-paclitaxel (3), the main metabolite of paclitaxel. Three different SALDI approaches have been tested employing nanostructure-assisted laser desorption/ionization (NALDI), carbon nanohorns (NHs) and carbon NHs covered by liquid additives. The results so obtained have been compared to those observed under matrix-assisted laser desorption/ionization (MALDI) conditions. Compounds 1 and 2 show the easy formation of protonated molecular species under all the experimental conditions, but the highest absolute intensity was achieved by NALDI. On the contrary, ionic species of low intensity are present for 3, among which are those that exhibit the highest intensity caused by [M + K]⁺ ions. After a critical evaluation of the obtained data, the linear response of the [M + H]⁺ ion intensity of 1 versus different deposited sample amounts was investigated, and the best results (R² = 0.9889) were obtained under MALDI conditions. The analysis of plasma samples spiked with 1 showed, again, that the MALDI approach was the best one (R² = 0.9766). The failure of NALDI measurements could be rationalized by the presence of ion-suppression effects.