Mass Spectrometry, Review of the Basics: Ionization

Abstract

Mass spectrometry (MS) has become an integral tool in life sciences. The first step in MS analysis is ion formation (ionization). Many ionization methods currently exist; electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are the most commonly used. ESI relies on the formation of charged droplets releasing ions from the surface (ion evaporation model) or via complete solvent evaporation (charge residual model). MALDI ionization, however, is facilitated via laser energy and the use of a matrix. Despite wide use, ESI cannot efficiently ionize nonpolar compounds. Atmospheric pressure chemical ionization (APCI) and atmospheric pressure photo ionization (APPI) are better suited for such tasks. APPI requires photon energy and a dopant, whereas APCI is similar to chemical ionization. In 2004, ambient MS was introduced in which ionization occurs at the sample in its native form. Desorption electrospray ionization (DESI) and direct analysis in real time (DART) are the most widely used methods. In this mini-review, we provide an overview of the main ionization methods and the mechanisms of ion formation. This article is educational and intended for students/researchers who are not very familiar with MS and would like to learn the basics; it is not for MS experts.

The Development of Novel Nanodiamond Based MALDI Matrices for the Analysis of Small Organic Pharmaceuticals

“…This is not surprising as the exact mechanism of ionization during MALDI-MS is not fully understood [6], with the vast majority of new matrices being introduced based on experimental data [31][32][33][34]. It is this fact that prompted us initially to evaluate a novel drug delivery agent ND-Lys as a MALDI matrix.…”

“…Because such clusters decrease spectral quality, thereby increasing detection limits, the analysis of small molecules such as pharmaceuticals is primarily carried out by other techniques like electrospray ionization (ESI). However, MALDI offers several advantages over ESI, including a simplified sample preparation, the formation of predominantly singly charged ions (which simplifies mass spectra), tolerance for additives and salts, and a much faster speed of analysis [6,7].…”

Paper-Based Electrochemical Cell Coupled to Mass Spectrometry

“…AMS provides the ability to perform chemical analyses of systems in their natural state, which has led to impactful discoveries in numerous research areas such as forensics, environmental science, and cancer biochemistry [45][46][47][48][49][50][51][52][53]. Recently, Chen and coworkers [11,[54][55][56][57][58] demonstrated that DESI can characterize liquid samples (liquid sampling DESI; LS-DESI) such as the effluent from chromatographic columns [59][60][61] and EC flow-cells [10,[62][63][64].…”

Multistage Reactive Transmission-Mode Desorption Electrospray Ionization Mass Spectrometry

“…The recent introduction of ambient mass spectrometric techniques [8][9][10][11][12][13][14][15] such as desorption electrospray ionization (DESI) [16] developed by Cooks and co-workers has revolutionized analytical chemistry in the past decade, allowing chemical analyses with minimal sample preparation. A recent advance developed by Zare and co-workers involves using DESI to capture short-lived solution-phase reaction intermediates (<1 ms) [17][18][19][20][21][22][23] at ambient conditions, while minimizing sample preparation times, carry over effects, and experimental complexity compared with ESI configurations.…”