Paper spray is developed as a direct sampling ionization method for mass spectrometric analysis of complex mixtures. Ions of analyte are generated by applying a high voltage to a paper triangle wetted with a small volume (<10 μL) of solution. Samples can be preloaded onto the paper, added with the wetting solution, or transferred from surfaces using the paper as a wipe. It is demonstrated that paper spray is applicable to the analysis of a wide variety of compounds, including small organic compounds, peptides, and proteins. Procedures are developed for analysis of dried biofluid spots and applied to therapeutic drug monitoring with whole blood samples and to illicit drug detection in raw urine samples. Limits of detection of 50 ng/mL (or 20 pg absolute) are achieved for atenolol in bovine blood. The combination of sample collection from surfaces and paper spray ionization also enables fast chemical screening at high sensitivity, for example 100 pg of heroin distributed on a surface and agrochemicals on fr...

Development, characterization, and application of paper spray ionization.

Kepa Ruiz-Mirazo,†,∥ Carlos Briones,‡,∥ and Andreś de la Escosura* †Biophysics Unit (CSIC-UPV/EHU), Leioa, and Department of Logic and Philosophy of Science, University of the Basque Country, Avenida de Tolosa 70, 20080 Donostia−San Sebastiań, Spain ‡Department of Molecular Evolution, Centro de Astrobiología (CSIC−INTA, associated to the NASA Astrobiology Institute), Carretera de Ajalvir, Km 4, 28850 Torrejoń de Ardoz, Madrid, Spain Organic Chemistry Department, Universidad Autońoma de Madrid, Cantoblanco, 28049 Madrid, Spain

Prebiotic systems chemistry: new perspectives for the origins of life.

Much has been made about J. L. W. Thudichum’s colorful, and one could say clairvoyant, naming of sphingosine “in commemoration of the many enigmas which it presented to the inquirer” in his 1884 treatise The Chemistry of the Brain(1) because many of the riddles of sphingolipids (as the broader field was later named)(2) remained unanswered for the following century. This changed radically over the past several decades as researchers explored, and ultimately established, what seemed at the time to be radical concepts: that sphingolipids are not just structural elements of cells but also participate in intra- and extracellular signaling; that not only the complex glycan headgroups, but also the lipid backbones, are highly specified metabolically and have selective biochemical functions; and that even the longest known function of these lipids, as structural components of the “fluid mosaic” of cell membrane lipids, is not so simple, and often involves the dynamic clustering of sphingolipids in nontraditional microdomains referred to as rafts. We still know only a fraction of their secrets, but this enlightenment has defined models for thinking about these compounds that remove them from their enigmatic “black box.”

Now, a major challenge is to keep up with the rapid growth in knowledge about the sphingolipidome, that is, the ensemble of all sphingolipids.(3) A major goal of the review is to help the reader more easily grasp the metabolic interrelationships that account for the tens of thousands of molecular subspecies (and perhaps more) that appear in nature, with a focus on mammals. The magnitude of this subject precludes the inclusion of all of the enzymes and metabolites, and the author apologizes for the omission of many interesting topics. To put this information in context, there is a brief background discussion of their structures and functions, which have been dealt with also in a recent Chemical Reviews article(4) on the chemicophysical features of sphingolipids and raft formation, and by excellent reviews on sphingolipid signaling5,6 and the biological functions of complex glycosphingolipids.7−10

Sphingolipid and Glycosphingolipid Metabolic Pathways in the Era of Sphingolipidomics

1.1. Mass Spectrometry
A mass spectrometer is described as the smallest weighing scale in the world ever used.1 Mass spectrometry (MS) is a unique technique that has an interdisciplinary nature, which freely crosses the borders of physics, chemistry and biology. Mass spectrometry makes a great scientific tool due to its capabilities to determine the mass of large biomolecular complexes, individual biomolecules, small organic molecules as well as single atoms and their isotopes. Right from the time of its invention in the first decade of the 20th century, mass spectrometry has undergone tremendous improvements in terms of its sensitivity, resolution and mass range. It currently finds applications in all scientific disciplines such as chemistry, physics, biology, pharmacology, medicine, biochemistry and bio-agro-based industry.

Introduction of “soft” ionization sources such as electrospray ionization (ESI) by J.B. Fenn et al.2 and matrix-assisted laser desorption/ionization (MALDI) by M. Karas et al.3 in 1980s revolutionized mass spectrometry as it offered the capability to analyze large intact biomolecules. As such MS became an irreplaceable tool for the biological sciences. The development of both ESI and MALDI made possible the ionization of smaller biomolecules such as drugs and metabolites as well larger biomolecules such as lipids, peptides and even proteins.2,4 The molecular weight (Mw) ranges we use in this review are defined as follows. The low Mw range includes elements and molecules from 1 to 500 Da. Molecules with Mw between 500 and 2000 Da fall in the medium Mw range. All molecules with Mw > 2000 Da are considered to be part of the high molecular weight class. It goes beyond the scope of this review to cover all developments in MS. Rather this review focuses on one of the latest, rapidly developing innovations in MS namely mass spectrometric imaging (MSI). This young technique takes benefit from all methodological and technological developments in general MS over the last decades. Over the last twenty years MSI has transformed from an esoteric, specialist technology studied by few researchers only to a technique that now finds itself at the center stage of mainstream MS. Over the last years the technology has matured to find applications in many different areas, with instrument developments taken up by all MS instrument manufacturers resulting in a rapid rise of the number of research groups active in this area. A thorough review of the area is therefore timely and needed to offer a starting point for all newcomers to the field. In this paper we describe and review approximately 20 years of MSI developement from the perspective of its application to biomedical imaging. We will emphasize the key research steps and pitfalls that determine the outcome of biological applications of this relatively new label free biomolecular imaging technique in life sciences.

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Mass spectrometric imaging for biomedical tissue analysis.

http://biostevera.com/wp-content/uploads/2014/11/02-Comprehensive-review.pdf

Stevia rebaudiana Bertoni, source of a high-potency natural sweetener: A comprehensive review on the biochemical, nutritional and functional aspects

Mass spectrometry imaging (MSI) has emerged as an important tool in the last decade and it is beginning to show potential to provide new information in many fields owing to its unique ability to acquire molecularly specific images and to provide multiplexed information, without the need for labeling or staining. In MSI, the chemical identity of molecules present on a surface is investigated as a function of spatial distribution. In addition to now standard methods involving MSI in vacuum, recently developed ambient ionization techniques allow MSI to be performed under atmospheric pressure on untreated samples outside the mass spectrometer. Here we review recent developments and applications of MSI emphasizing the ambient ionization techniques of desorption electrospray ionization (DESI), laser ablation electrospray ionization (LAESI), probe electrospray ionization (PESI), desorption atmospheric pressure photoionization (DAPPI), femtosecond laser desorption ionization (fs-LDI), laser electrospray mass spectrometry (LEMS), infrared laser ablation metastable-induced chemical ionization (IR-LAMICI), liquid microjunction surface sampling probe mass spectrometry (LMJ-SSP MS), nanospray desorption electrospray ionization (nano-DESI), and plasma sources such as the low temperature plasma (LTP) probe and laser ablation coupled to flowing atmospheric-pressure afterglow (LA-FAPA). Included are discussions of some of the features of ambient MSI for example the ability to implement chemical reactions with the goal of providing high abundance ions characteristic of specific compounds of interest and the use of tandem mass spectrometry to either map the distribution of targeted molecules with high specificity or to provide additional MS information on the structural identification of compounds. We also describe the role of bioinformatics in acquiring and interpreting the chemical and spatial information obtained through MSI, especially in biological applications for tissue diagnostic purposes. Finally, we discuss the challenges in ambient MSI and include perspectives on the future of the field.

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Mass spectrometry imaging under ambient conditions.

Mass spectrometry allows rapid chemical analysis of untreated samples in the ambient environment. This is a result of recent rapid progress in ambient ionization techniques. The most widely studied of these new methods, desorption electrospray ionization (DESI), uses fast-moving solvent droplets to extract analytes from surfaces and propel the resulting secondary microdroplets towards the mass analyzer. This review of DESI and other ambient methods centers on the accompanying chemical processes. Manipulation of the chemistry accompanying ambient ionization can be used to optimize chemical analysis, including molecular imaging. Solvent effects, geometry effects, electrochemical processes and mechanisms are covered. Extensions of the methodology to solution-phase analysis, to stand-off detection and to therapeutic drug analysis using miniature mass spectrometers are also treated.

Desorption electrospray ionization and other ambient ionization methods: current progress and preview

Direct and rapid analysis of cholesterol was accomplished in the ambient environment using reactive desorption electrospray ionization (DESI) mass spectrometry. This was achieved by electrospraying reagent solutions in the form of high velocity charged droplets at surfaces such as dried serum samples and animal tissue sections. Betaine aldehyde, incorporated into the spray solvent, reacts selectively and rapidly with the alcohol group of cholesterol by nucleophilic addition, forming a hemiacetal salt. Limits of detection for pure cholesterol and related compounds were ∼1 ng when a solution of cholesterol of 1 μg/mL was spotted onto the surface. Quantitative analysis of free cholesterol in serum using reactive DESI was demonstrated using cholesterol-d7 as internal standard. High throughput analysis of small volumes of serum spotted onto a suitable substrate was achieved at an analysis rate of ∼14 s per sample, with a relative standard deviation (RSD) of ca. 6%. Use of reactive DESI in the imaging mode allo...

/pdf/rapid-direct-analysis-of-cholesterol-by-charge-labeling-in-3iftygi872.pdf

Rapid, Direct Analysis of Cholesterol by Charge Labeling in Reactive Desorption Electrospray Ionization

Two-dimensional (2D) imaging mass spectrometry (MS)[1] has emerged as a powerful technique in the biological sciences. It allows direct investigation of the distribution of a variety of lipids, drugs, biological defensive agents, pigments and proteins in plant and animal tissues with high specificity and without the need of fluorescent or radioactive labelling normally used in histochemical protocols.[2, 3] In imaging MS, the chemical identity of molecules present on a surface is investigated as a function of their 2D spatial distribution (x and y coordinates).

/pdf/three-dimensional-vizualization-of-mouse-brain-by-lipid-3rzpfncftd.pdf

Three-Dimensional Vizualization of Mouse Brain by Lipid Analysis Using Ambient Ionization Mass Spectrometry

The analysis of Stevia leaves has been demonstrated without any sample preparation using desorption electrospray ionization (DESI) mass spectrometry. Direct rapid analysis was achieved using minimal amounts of sample (∼0.15 cm × 0.15 cm leaf fragment). Characteristic constituents of the Stevia plant are observed in both the positive and negative ion modes including a series of diterpene ‘sweet’ glycosides. The presence of the glycosides was confirmed via tandem mass spectrometry analysis using collision-induced dissociation and further supported by exact mass measurements using an LTQ-Orbitrap. The analysis of both untreated and hexane-extracted dry leaves proved that DESI can be successfully used to analyze untreated leaf fragments as identical profiles were obtained from both types of samples. Characterization and semi-quantitative determination of the glycosides was achieved based on the glycoside profile within the full mass spectrum. In addition, the presence of characteristic glycosides in an all-natural commercial Stevia dietary supplement was confirmed. This study provides an example of the application of DESI to direct screening of plant materials, in this case diterpene glycosides.

Chunping Wu

Papers

Mass spectrometry imaging under ambient conditions.

Desorption electrospray ionization and other ambient ionization methods: current progress and preview

Rapid, Direct Analysis of Cholesterol by Charge Labeling in Reactive Desorption Electrospray Ionization

Three-Dimensional Vizualization of Mouse Brain by Lipid Analysis Using Ambient Ionization Mass Spectrometry

Direct analysis of Stevia leaves for diterpene glycosides by desorption electrospray ionization mass spectrometry