In Situ Separation and Analysis of Lipids by Paper Spray Ionization Mass Spectrometry

Youngju Kal,Sangwon Cha

doi:10.3390/molecules26010093

Abstract

Paper spray ionization (PSI) is an extractive ambient ionization technique for mass spectrometry (MS), whereby a triangular paper tip serves as the sampling base and the electrospray tip. During PSI, analytes are extracted and transported to the edge of the paper tip by the applied spraying solvent. Analytes can be purified from a sample matrix and separated from each other by this transportation process. In this study, we investigated and utilized the analyte transportation process of PSI for the in situ separation and analysis of lipid mixtures. We found that differential transport of phosphatidylcholine (PC) and triacylglycerol (TAG), the two most abundant lipid classes in animals, occurred during PSI. We also found that the order in which these lipids moved strongly depended on how the spraying solvent was applied to the paper base. The more polar PC moved faster than the less polar TAG during PSI, when a polar solvent was slowly fed into a paper tip, whereas TAG was transported faster than PC when excess solvent was applied to the tip at once. In addition, we achieved a complete separation and detection of PC and TAG by slowly supplying a nonpolar solvent to a PSI tip.

Highlights

Ambient ionization methods for mass spectrometry (MS) have become immensely popular, as their convenience and raw material analysis capabilities are unapparelled [1,2]
We investigated the analyte transportation process of paper spray ionization (PSI) in the case of a mixture of two compounds belonging to the two most abundant lipid families found in animal lipid extracts: phosphatidylcholine (PC) and triacylglycerol (TAG)
We selected two different lipids, a PC and a TAG, which are the most abundant lipid species found in animal lipid extracts, with the goal of exploring the issue of how lipids move on a paper tip during PSI MS in a manner dependent on the solvent application method

Summary

Introduction

Ambient ionization methods for mass spectrometry (MS) have become immensely popular, as their convenience and raw material analysis capabilities are unapparelled [1,2]. In PSI, a planar triangular-shaped paper is used as an electrospray tip, a sampling base, and a separation medium. A liquid-phase sample is loaded onto the paper tip and dried; subsequently, a high voltage and spraying solvent are applied to paper [6]. These steps result in analyte transportation through the paper tip and ion generation at the edge of the paper tip via ESI-like processes, after which the generated analyte ions are directed to the mass spectrometer [6,9]

Methods

Results

Conclusion