Polarization induced electrospray ionization mass spectrometry for the analysis of liquid, viscous and solid samples

Abstract

In this study, a polarization-induced electrospray ionization mass spectrometry (ESI-MS) was developed. A micro-sized sample droplet was deposited on a naturally available dielectric substrate such as a fruit or a stone, and then placed close to (~2 mm) the orifice of a mass spectrometer applied with a high voltage. Taylor cone was observed from the sample droplet, and a spray emitted from the cone apex was generated. The analyte ion signals derived from the droplet were obtained by the mass spectrometer. The ionization process is similar to that in ESI although no direct electric contact was applied on the sample site. The sample droplet polarized by the high electric field provided by the mass spectrometer initiated the ionization process. The dielectric sample loading substrate facilitated further the polarization process, resulting in the formation of Taylor cone. The mass spectral profiles obtained via this approach resembled those obtained using ESI-MS. Multiply charged ions dominated the mass spectra of peptides and proteins, whereas singly charged ions dominated the mass spectra of small molecules such as amino acids and small organic molecules. In addition to liquid samples, this approach can be used for the analysis of solid and viscous samples. A small droplet containing suitable solvent (5-10 µl) was directly deposited on the surface of the solid (or viscous) sample, placed close the orifice of mass spectrometer applied with a high voltage. Taylor cone derived from the droplet was immediately formed followed by electrospray processes to generate gas-phase ions for MS analysis. Analyte ions derived from the main ingredients of pharmaceutical tablets and viscous ointment can be extracted into the solvent droplet in situ and observed using a mass spectrometer.

Ultrasonication‐assisted spray ionization‐based micro‐reactors for online monitoring of fast chemical reactions by mass spectrometry

“…It is understandable because applying direct electric‐contact on the capillary outlet can lead to generation of solvent background ions through electrochemical reaction. It is also the reason why we usually did not apply any electric contact directly on the emitter in our approaches . That is, to apply any electric contact on the capillary outlets is not necessary.…”

Analysis of pharmaceutical products and herbal medicines using ambient mass spectrometry

“…Polarization induced ESI was reported by Meher and Chen in 2015 [120], and the active pharmaceutical ingredients in paracetamol tablet, baclofen tablets, and miconazole ointment were successfully detected by this technique.…”

“…These techniques were developed mainly for rapid, direct, real-time, in situ, and in vivo analysis of biological tissues, and they are suitable for direct analysis of raw herbal medicines without sample pretreatment. The reported tissue electrospray ionization techniques which have been applied for analysis of pharmaceutical products and herbal medicines mainly include tissue spray ionization [113], leaf spray [114][115][116], direct plant spray [117], direct ionization (DI) [118], field-induced DI [119], polarization induced ESI [120], and internal extractive electrospray ionization (iEESI) [121]. Although the names of these techniques are different, their mechanisms and analytical strategies are similar.…”

Electrospray Modifications for Advancing Mass Spectrometric Analysis

“…e pressure di erence at the same point allowed the droplet to enter MS ori ce, leading to generation of gas-phase ions. 87) Recently, another method, called as polarization induced electrospray ionization (PI-ESI), 88) was reported by the same group. Electrospray can be directly generated from a microliter-size droplets (4-10 µL) that is placed over a dielectric material (e.g., a cherry tomato), which is placed close to the inlet of a mass spectrometer, applied with a high voltage (Fig.…”

“…e obtained mass spectral pro les acquired using this method are similar to those obtained in conventional ESI mass spectra. Only a dielectric substrate for holding a sample droplet is required in PI-ESI, 88) which is probably one of the simplest ESI variants that have been ever reported. One major advantage of PI-ESI is the avoidance of dead volume and adsorption surfaces which is typically seen in regular ESI.…”