Ultrahigh-Throughput and Chromatography-Free Bioanalysis of Polar Analytes with Acoustic Ejection Mass Spectrometry

Abstract

Bioanalysis of polar analytes using liquid chromatography – tandem mass spectrometry (LC-MS/MS) remains a significant challenge, due to their poor chromatographic retention on the commonly used reversed-phase LC columns, and the resulting severe ionization suppression from co-eluting matrix components. Here we present a novel approach to perform ultrahigh-throughput and chromatography-free bioanalysis of polar compounds, using a prototype acoustic ejection mass spectrome-ter (AEMS) platform. Previously developed for direct analysis of solid or liquid samples by MS, the open port interface (OPI) has recently been modified and coupled to an acoustic nanoliter dispenser to enable high-speed direct MS analysis from 384-well plates with a reported speed as fast as 0.5 second per sample. Ionization suppression was reduced due to the >1000 fold dilution of the original sample by the carrier solvent in the AE-OPI-MS operation. Taking full advantage of the chroma-tography-free and suppression-reducing features of this prototype instrument, we successfully demonstrated the ultrahigh-throughput bioanalysis of metformin, a small polar substrate commonly used in high-throughput in vitro transporter inhibi-tion assays in the early ADME profiling space in drug discovery. The AEMS platform achieved a speed of 2.2 sec-onds/sample using only 10 nL of sample volume. Similar bioanalytical and biological results from actual assay samples were obtained by AEMS when compared to those obtained by the fastest LC-MS/MS method previously reported, along with a 15-fold speed advantage, and a ~500-fold less sample consumption to enable future assay miniaturization. The gen-eral applicability of this novel approach to bioanalysis of several classes of polar analytes including ethambutol, isoniazid, ephedrine and gemcitabine in biological matrices was further demonstrated.