Surface analysis using a new plasma assisted desorption/ionisation source for mass spectrometry in ambient air

The development and application of matrix assisted laser desorption electrospray ionization: The teenage years

In the past 15 years, ambient ionization techniques have witnessed a significant incursion into the field of mass spectrometry imaging, demonstrating their ability to provide complementary information to matrix-assisted laser desorption ionization. Matrix-assisted laser desorption electrospray ionization is one such technique that has evolved since its first demonstrations with ultraviolet lasers coupled to Fourier transform-ion cyclotron resonance mass spectrometers to extensive use with infrared lasers coupled to orbitrap-based mass spectrometers. Concurrently, there have been transformative developments of this imaging platform due to the high level of control the principal group has retained over the laser technology, data acquisition software (RastirX), instrument communication, and image processing software (MSiReader). This review will discuss the developments of MALDESI since its first laboratory demonstration in 2005 to the most recent advances in 2021.

Exploration and performance evaluation of microwave-induced plasma with different discharge gases for ambient desorption/ionization mass spectrometry

RATIONALE

Microwave-induced plasma (MIP) with different discharge gases of argon or helium provides significant plasma-based ambient desorption/ionization sources, which have potential applicability in direct analysis of complex samples without any sample pre-treatment. In this study, experiments were conducted to better understand microwave-induced plasma desorption/ionization (MIPDI) sources and the corresponding ionization mechanisms.

METHODS

Emission spectra of microwave-induced argon (MIP-Ar) and helium (MIP-He) plasmas were obtained from the plasma tail flame of a MIP source. Compounds including L-phenylalanine, L-serine, L-valine, urea, 4-acetaminophen, gallic acid and L-ascorbic acid were analyzed using both sources. Polyethylene glycol 400 (PEG400) oligomers were detected by MIP-Ar and MIP-He mass spectrometry at different microwave powers. Mass spectra of higher molecular weight PEGs (including PEG800, PEG1000 and PEG2000) were also acquired using both sources.

RESULTS

In the emission spectra, N₂ , H-I and O-I species were observed by MIP-Ar/He. In addition, SiO₂ , Na-I, Si-I and Si-II species were generated by MIP-He. In the mass spectra of compounds, [M+H]⁺ , [2M+H]⁺ , [M+O+H]⁺ , [M+2O-H]⁺ and fragment ions were observed. In the mass spectra of PEG400 obtained by MIP-Ar/He at different microwave powers, higher molecular weight oligomers could only be observed with higher microwave power. PEGs with molecular weights as high as 1000 Da were also successfully analyzed by MIPDI.

CONCLUSIONS

According to the different natures of the samples, either MIP-Ar or MIP-He can be chosen as a working ion source for mass spectrometry. The MIPDI source is potentially applicable to the analysis of compounds with high molecular weights, especially polymers with high degree of polymerization (such as PEG2000), which is a challenging issue for the traditional ambient ionization sources. Copyright © 2017 John Wiley & Sons, Ltd.

Mass spectrometry based chemical imaging of foods

Chemical imaging based on mass spectrometry is an emerging technology which has opened opportunities for fundamental research in food science.

Solid-phase microextraction low temperature plasma mass spectrometry for the direct and rapid analysis of chemical warfare simulants in complex mixtures

Sensitive, rapid, and direct detection of chemical-warfare agent simulants in urine by solid-phase microextraction low temperature plasma ionisation mass spectrometry.

Ambient ionization MS for bioanalysis: recent developments and challenges

Ambient ionization MS has become very popular in analytical science and has now evolved as an effective analytical tool in metabolomics, biological tissue imaging, protein and small molecule drug analysis, where biological samples are probed in a rapid and direct fashion with minimal sample preparation at ambient conditions. However, certain inherent challenges continue to hinder the vibrant prospects of these methods for in situ analyses or to replace conventional methods in bioanalysis. This review provides an introduction to the field and its application in bioanalysis, with an emphasis on the most recent developments and applications. Furthermore, ongoing challenges or limitations related to quantitation, sensitivity, selectivity, instrumentation and mass range of these ambient methods will also be discussed.

Comparison of three plasma sources for ambient desorption/ionization mass spectrometry

Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources.

Characterisation of a micro-plasma for ambient mass spectrometry imaging

A systematic characterisation and optimisation of parameters of a plasma-mediated ion source to achieve the best spatial resolution for MSI.