Revisiting the quantitative features of surface-assisted laser desorption/ionization mass spectrometric analysis

Continuous synthesis of BaFe2O4 and BaFe12O19 nanoparticles in a droplet microreactor for efficient detection of antihistamine drugs in oral fluid using surface-assisted laser desorption/ionization mass spectrometry

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) has received considerable attention as a complementary approach to matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), offering substantial potential for analyzing molecules in the low-mass region. Herein, we propose a facile method, a microreactor for the synthesis of two types of barium ferrite (BaFe2O4 and BaFe12O19) nanoparticles (NPs) within moving droplets for detecting antihistamine (AH) drugs in oral fluid (OF). The synthesized BaFe2O4 and BaFe12O19 NPs exhibited small particle size, good ultraviolet absorption, and excellent performance in SALDI-MS, as determined by survival yield measurements. The limits-of-detection for AH drugs were in the range of 1 pg mL-1 to 100 ng mL-1, and spot-spot reproducibility of the SALDI substrates was satisfactory. Moreover, when analyzing cetirizine in OF, the obtained recoveries of cetirizine were 101% and 99% using BaFe2O4 and BaFe12O19 NP, respectively. Furthermore, the proposed method was validated by analyzing OF samples from a healthy volunteer who consumed a 5 mg levocetirizine tablet for seven days. SALDI-MS analysis confirmed the successful detection of endogenous components, the parent ion of cetirizine, and other exogenous substances. This study reports an advanced application of droplet microreactor technology for designing and synthesizing a wide range of novel and efficient SALDI-MS substrates for various applications.

Single-Walled Carbon Nanohorns as Boosting Surface for the Analysis of Low-Molecular-Weight Compounds by SALDI-MS

Limits of Matrix-Assisted Laser Desorption Ionization (MALDI) mass spectrometry (MS) in the study of small molecules are due to matrix-related interfering species in the low m/z range. Single-walled carbon nanohorns (SWCNH) were here evaluated as a specific surface for the rapid analysis of amino acids and lipids by Surface-Assisted Laser Desorption Ionization (SALDI). The method was optimized for detecting twenty amino acids, mainly present as cationized species, with the [M+K]⁺ response generally 2-time larger than the [M+Na]⁺ one. The [M+Na]⁺/[M+K]⁺ signals ratio was tentatively correlated with the molecular weight, dipole moment and binding affinity, to describe the amino acids’ coordination ability. The SWCNH-based surface was also tested for analyzing triglycerides in olive oil samples, showing promising results in determining the percentage composition of fatty acids without any sample treatment. Results indicated that SWCNH is a promising substrate for the SALDI-MS analysis of low molecular weight compounds with different polarities, enlarging the analytical platforms for MALDI applications.