An overview of biological applications and fundamentals of newinletandvacuumionization technologies

Abstract

Rationale The developments of new ionization technologies based on processes previously unknown to mass spectrometry (MS) have gained significant momentum. Herein we address the importance of understanding these unique ionization processes, demonstrate the new capabilities currently unmet by other methods, and outline their considerable analytical potential. Methods The inlet and vacuum ionization methods of solvent‐assisted ionization (SAI), matrix‐assisted ionization (MAI), and laserspray ionization can be used with commercial and dedicated ion sources producing ions from atmospheric or vacuum conditions for analyses of a variety of materials including drugs, lipids, and proteins introduced from well plates, pipet tips and plate surfaces with and without a laser using solid or solvent matrices. Mass spectrometers from various vendors are employed. Results Results are presented highlighting strengths relative to ionization methods of electrospray ionization (ESI) and matrix‐assisted laser desorption/ionization. We demonstrate the utility of multi‐ionization platforms encompassing MAI, SAI, and ESI and enabling detection of what otherwise is missed, especially when directly analyzing mixtures. Unmatched robustness is achieved with dedicated vacuum MAI sources with mechanical introduction of the sample to the sub‐atmospheric pressure (vacuum MAI). Simplicity and use of a wide array of matrices are attained using a conduit (inlet ionization), preferably heated, with sample introduction from atmospheric pressure. Tissue, whole blood, urine (including mouse, chicken, and human origin), bacteria strains and chemical on‐probe reactions are analyzed directly and, especially in the case of vacuum ionization, without concern of carryover or instrument contamination. Conclusions Examples are provided highlighting the exceptional analytical capabilities associated with the novel ionization processes in MS that reduce operational complexity while increasing speed and robustness, achieving mass spectra with low background for improved sensitivity, suggesting the potential of this simple ionization technology to drive MS into areas currently underserved, such as clinical and medical applications.

Sublimation Driven Ionization for Use in Mass Spectrometry: Mechanistic Implications

“…In MALDI, a laser is used to impart thermal energy into the matrix which may be responsible for the observation of low charge states. Charge stripping in ESI by addition of energy , and lower charge states in MAI with added energy , are examples supporting this hypothesis.…”

A Combination MAI and MALDI Vacuum Source Operational from Atmospheric Pressure for Fast, Robust, and Sensitive Analyses

“…In some cases, vMAI has produced higher sensitivity and selectivity compared to ESI or vacuum MALDI-TOF. , The ability to acquire 24 samples by vMAI in 4 min, disregarding the ca. 2 min to introduce the sample plate into the vacuum of the mass spectrometer, was demonstrated on a Waters SYNAPT G2S mass spectrometer . Matrix combinations (mixtures) ,− or additives, such as ammonium salts, − can be utilized to enhance the effectiveness of analyte ionization providing more specificity or breadth and depth analyzing complex samples.…”

“…With vMAI, proteins as large as bovine serum albumin (BSA) (66 kDa) were observed without engaging the laser using commercial intermediate pressure MALDI and ESI and atmospheric pressure chemical ionization (APCI) sources on API mass spectrometers made possible because of the formation of multiply charged ions. , Examples of biomedical and clinical relevance include, as representative examples, analysis of drugs of abuse, metabolites, , gangliosides, membrane proteins, and various toxins and other potential health hazard materials . Quantification of proteins and drugs as well as bacterial differentiation have been demonstrated. ,, Because of multiply charging, high performance mass spectrometers with well-known advantages such as mass accuracy, mass resolution, as well as other advanced measurement technologies such as electron transfer dissociation (ETD) ,− are applicable. As samples become increasingly complex, high performance mass spectrometers become more critical, as does advanced data analyses for accurate and fast analyses. ,, …”

Navigate flying molecular elephants safely to the ground: mass-selective soft landing up to the Mega-Dalton range by Electrospray Controlled Ion-Beam Deposition

“…In the analytical field, they are the basis of commercial mass spectrometers. The ions typically originate from an Electrospray Ionization (ESI) source, a cluster source, Matrix-Assisted Laser Desorption Ionization (MALDI) 1,2 , or from molecules gathered from a surface under ambient conditions by Desorption ESI (DESI) 3,4 or Direct Analysis in Real Time (DART) 2,5 even directly from the tissue of living organisms. The ions are guided through differentially pumped vacuum stages and analytical devices, finally they are detected while discarded irreversibly.…”