Electron ionization mass spectrometry: Quo vadis?

Abstract

Mass spectrometry (MS) is a fundamental technique to identify compounds by their mass-to-charge ratio. It is known that MS can only detect target compounds when they are converted to ions in the gas phase. The ionization procedure is considered one of the most critical steps, and there are distinct techniques for it. One of them is electron ionization (EI), a widely used hard-ionization technique capable of generating several ions due to the excess energy employed. The existence of distinct ionization mechanisms turns EI capable of producing a fingerprintlike spectrum for each molecule. So, it is an essential technique for obtaining structural information. EI is often combined with chromatography to obtain a practical introduction of pretreated samples despite its excellent performance. EI-MS has been applied coupled with gas chromatography (GC) since the 1960s as both are very compatible. Currently, analytes of interest are more suitable for liquid chromatography (LC) analysis, so there are researchers dedicated to developing suitable interfaces for coupling LC and EI-MS. EI excels, as a reliable technique to fill the gap between GC and LC, possibly allowing them to coexist in a single instrument. In this work, the authors will present the fundamentals of EI-MS, emphasizing the development over the years, coupling with gas and LC, and future trends.

Open tubular liquid chromatography: Recent advances and future trends

“…Nevertheless, the modern developments in nanoLC have allowed for mitigating the impacts of the mobile phase over the EI process. The techniques are becoming compatible through interfaces such as the Direct-EI, Liquid electron ionization (LEI), and the Cold-EI [102,103].…”

Portable mass spectrometry system: instrumentation, applications, and path to ‘omics analysis

“…Electron ionization (EI, also called electron impact ionization in early literature), was one of the most commonly used ionization methods for MS analysis. It utilizes the interaction between electrons and gas phase molecules to ionize the molecules [22,23]. EI often generates fragment ions during the ionization process.…”

Kinematic viscosity prediction of jet fuels and alternative blending components via comprehensive two‐dimensional gas chromatography, partial least squares, and Yeo‐Johnson transformation

“…Aligned to these principles, this work proposes for the first time the use of GC × GC coupled to a flame ionization detector (GC × GC/FID) as a powerful option to fill this gap given the ability of this analytical technique to both separate at least an order of magnitude more compounds compared to conventional one-dimensional GC and to provide more detailed chemical information of complex mixtures compared to infrared spectroscopy [17,[36][37][38]. Additionally, GC × GC/FID provides remarkably better quantitation capabilities with response factors close to one for hydrocarbons unlike MS detectors while avoiding the challenge of different ionization efficiencies during electron and chemical ionization mechanisms and biases towards specific hydrocarbon groups especially when alternative blending components are analyzed via ASTM D2425 [39][40][41][42][43]. Thus, this work exhibits the applicability of GC × GC/FID and PLS to predict the kinematic viscosity of jet fuels and alternative blending components at −20 • C. Additionally, this model shows the influence of different normalization methods (mean centering normal-ization, logarithmic, and Yeo-Johnson transformations) over the PLS performance metrics.…”