Direct coupling of commercial coated blades with low-temperature plasma ionization mass spectrometry by micro-solvent aided soft thermal desorption.

Coated blades have been widely used with ambient ionization mass spectrometry (AIMS) using electrospray as ionization source. This article explores the coupling of commercial blades, containing hydrophilic-lipophilic balance particles (HLB), with soft ionization by chemical reaction in transfer mass spectrometry using a dedicated thermal desorber as interface. Commercial HLB-blades use polyacrylonitrile to embed the sorptive particles in the coating, but this binder is not fully compatible with the high temperatures required to efficiently desorb semivolatile compounds, such as those selected in this work (cocaine, codeine, methadone, and methamphetamine). To overcome this limitation, a micro-solvent-aided soft thermal desorption is proposed. For this purpose, 4 µL of octanol is deposited on the blade before placing it in the desorber, thereby assisting the chemical elution of the analytes and enabling thermal desorption at mild conditions (about 100 °C) in 1.5 min. As proof-of-concept, this strategy has been used to determine the drugs mentioned above in saliva, with detection limits as low as 0.6 µg L- 1. The method has been evaluated according to selected ICH M10 criteria to demonstrate its potential fully. As many samples can be extracted simultaneously, this approach provides a high throughput that surpasses the provided by classical liquid chromatography-mass spectrometry analysis. The new approach will permit to extend the application of coated blades to other analytes (e.g. hydrocarbons) that are poorly ionized by ESI.