Matrix-Compatible Solid-Phase Microextraction Pin Coupled Directly to Mass Spectrometry using Probe Electrospray Ionization

A solid-phase microextraction (SPME) pin device with a biocompatible coating on the tip was developed for direct coupling to mass spectrometry (MS) via a vertical dipping-and-spray strategy using an automated probe electrospray ionization (PESI) interface. The developed method provides superior sensitivity compared to standard PESI-MS due to the enrichment effects of SPME and the significant increase in the volume of sample and/or solvent collected during dipping due to the SPME pin's notably larger size. The tips of the SPME pins were coated with a biocompatible coating consisting of small sorbent particles embedded into a polyacrylonitrile (PAN) binder. This coating enables the extraction of small molecules, while preventing larger molecules such as tissue fragments, proteins, and cell matter from coming into the sorbent. The developed SPME pin-PESI-MS method also features much lower matrix effects compared to PESI-MS for the analysis of complex biology samples. When applied for the analysis of 8 drugs of abuse in urine samples, the SPME pin-PESI-MS method provided good linearity (R² ≥ 0.9997), high sensitivity with limits of detection between 0.003 to 0.03 ng/mL, and good reproducibility with RSD% ≤ 6%. The vertical design of the SPME-PESI-MS direct-coupling interface allows the potential fully automation of the system using a conventional autosampler.