Matrix-assisted Laser Desorption/ionization Technique Research Articles

Recent Trends in MALDI-MS Drugs Analysis in Human Hair: Pre-Analytical and Analytical Challenges and Pitfalls.

The value of hair in forensic toxicology has already been widely demonstrated. It offers a much wider detection window than other matrices, and its segmental analysis allows the documentation of a single, occasional or regular consumption of a large number of molecules. To date, considerable efforts are being made to achieve very high sensitivity using increasingly effective techniques in the forensic analysis of hair (gas chromatography with electron ionization mass spectrometry (GC--EI-MS); gas chromatography with chemical ionization mass spectrometry (GC--CI-MS); gas chromatography-tandem mass spectrometry (GC--MS-MS); high or ultra performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS and UPLC-MS-MS)). Since the early 2000s, work has been carried out to analyze hair using matrix-assisted laser desorption ionization (MALDI) coupled with imaging mass spectrometry (IMS). Intact, cut or pulverized, human head hairs are analyzed in all their forms. With a simplified and rapid sample preparation protocol, MALDI-IMS appears to be an attractive option for the forensic interpretation of hair analysis. The high spatial resolution clearly competes with conventional methods and strand segmentation. This article provides a complete overview on MALDI techniques used and its applications to better understand the pre-analytical and the analytical parts in the hair analysis.

Evaluation of 6 MALDI-Matrices for 10 μm Lipid Imaging and On-Tissue MSn with AP-MALDI-Orbitrap.

Mass spectrometry imaging is a technique uniquely suited to localize and identify lipids in a tissue sample. Using an atmospheric pressure (AP-) matrix-assisted laser desorption ionization (MALDI) source coupled to an Orbitrap Elite, numerous lipid locations and structures can be determined in high mass resolution spectra and at cellular spatial resolution, but careful sample preparation is necessary. We tested 11 protocols on serial brain sections for the commonly used MALDI matrices CHCA, norharmane, DHB, DHAP, THAP, and DAN in combination with tissue washing and matrix additives to determine the lipid coverage, signal intensity, and spatial resolution achievable with AP-MALDI. In positive-ion mode, the most lipids could be detected with CHCA and THAP, while THAP and DAN without additional treatment offered the best signal intensities. In negative-ion mode, DAN showed the best lipid coverage and DHAP performed superiorly for gangliosides. DHB produced intense cholesterol signals in the white matter. One hundred fifty-five lipids were assigned in positive-ion mode (THAP) and 137 in negative-ion mode (DAN), and 76 peaks were identified using on-tissue tandem-MS. The spatial resolution achievable with DAN was 10 μm, confirmed with on tissue line-scans. This enabled the association of lipid species to single neurons in AP-MALDI images. The results show that the performance of AP-MALDI is comparable to vacuum MALDI techniques for lipid imaging.

Effect of Seed Dressing and Soil Chemical Properties on Communities of Microorganisms Associated with Pre-Emergence Damping-Off of Broad Bean Seedlings

Combating soil pathogens that disable plant emergence is among the most difficult challenges of global agriculture. Legumes, preferred in sustainable cultivation systems, are particularly sensitive to pre-emergence damping-off of seedlings. Seed dressing is therefore a very important element in the cultivation technology. The aim of this study was to compare the impact of biological (Pythium oligandrum) and chemical (carboxin + thiuram) seed dressing on the quantitative and qualitative composition of microorganisms participating in the epidemiology of this disease, under specific hydrothermal conditions and chemical properties of the soil (pH, humus, macro-, and micronutrient). Microorganism identification was done using the MALDI-TOF MS (Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) technique. Species were assigned to frequency groups, and populations of pathogens, saprophytes, and antagonists were identified. The biodiversity of these communities was expressed with Simpson’s Reciprocal, Shannon–Wiener, and Evenness (Shannon) indices. In individual variants of seed pre-treatment, the correlations between individual edaphic factors and the suppression of pre-emergence damping-off, the number of isolates obtained from infected seedlings, and the share of individual trophic groups of fungi were assessed. The main causes of pre-emergence damping-off of broad bean seedlings are Ilyonectria destructans, Globisporangium irregulare, Fusarium equiseti, Rhizoctonia solani, and Fusarium solani. Eliminating seed treatment results in a seedling mortality rate of 33.5–42.5%. The effectiveness of the chemical protection product is 44.2% and 25.9%. Carboxin and thiuram reduce the diversity of microorganisms involved in the pathogenesis of pre-emergence damping-off and limit the presence of antagonistic fungi. Under the influence of P. oligandrum, there was a five-fold increase in the population of antagonists. An increase in humus in the soil reduces the percentage of diseased broad bean seedlings.

MASS SPECTROMETRY FOR A HOLISTIC VIEW OF NATURAL EXTRACTS OF PHYTOTHERAPEUTIC INTEREST.

In the study of natural products new strategies which favor a holistic approach, integrating the traditional reductionist methods usually employed, have been proposed. In this frame, the studies carried out by us in the last decade show that fingerprints, mainly obtained by electrospray ionization mass spectrometry (ESI-MS), lead to the characterization of natural extracts from different botanical species but also of phytotherapeutic products constituted by mixtures of extracts from different plants. Laser desorption ionization and matrix-assisted laser desorption ionization techniques were also employed and by the use of different matrices some complementary results were achieved. Results obtained by standard spectrophotometric and liquid chromatography methods were compared with those achieved by direct infusion of the extract in ESI-MS conditions, indicating an excellent agreement between the two approaches. The findings of these researches were considered in the frame of complex systems theory, investigating how relationships between a system's parts can give rise to its collective behaviors and how the system interacts and forms relationships with its environment. In this view, the peculiar pharmacological behavior of biologically active natural compounds can be justified by the occurrence of molecular interactions due to the high complexity of the natural matrix. Some of these interactions have been widely studied in the case of green tea extracts (GTEs) proving unequivocally the presence of caffeine/catechin complexes in GTE samples. The presence of bimolecular complexes has been observed also in the case of Ceylon tea and Mate extracts. These data indicate that the formation of complexes in natural extracts is a common behavior and their presence must be considered in the description of natural extracts and, consequently, in their biological activity. ©2020 John Wiley & Sons Ltd. Mass Spec Rev.

Mass Spectrometry Detection of Nitrobenzoic Acids and Their Salts on the Surface of Construction Materials

The application of mass spectrometry to the detection of m-nitrobenzoic and 3,5-dinitrobenzoic acids and their salts on the surface of construction materials used in rocketry is described. Analytes are washed with acetonitrile from the studied surface and then analyzed by HPLC−MS with electrospray ionization or the matrix assisted laser desorption/ionization (MALDI). For electrospray ionization, the limit of detection is 6 μg/L and for MALDI ionization, 2 μg/L. The MALDI technique also ensures the direct investigation of samples without washing out; in this case, mass spectra can be visualized by constructing 2D diagrams of the distribution of nitrobenzoic acids over the surface.

Advances in mass spectrometry-based metabolomics for investigation of metabolites.

Metabolomics is the systematic study of all the metabolites present within a biological system, which consists of a mass of molecules, having a variety of physical and chemical properties and existing over an extensive dynamic range in biological samples. Diverse analytical techniques are needed to achieve higher coverage of metabolites. The application of mass spectrometry (MS) in metabolomics has increased exponentially since the discovery and development of electrospray ionization and matrix-assisted laser desorption ionization techniques. Significant advances have also occurred in separation-based MS techniques (gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, capillary electrophoresis-mass spectrometry, and ion mobility-mass spectrometry), as well as separation-free MS techniques (direct infusion-mass spectrometry, matrix-assisted laser desorption ionization-mass spectrometry, mass spectrometry imaging, and direct analysis in real time mass spectrometry) in the past decades. This review presents a brief overview of the recent advanced MS techniques and their latest applications in metabolomics. The software/websites for MS result analyses are also reviewed.

Characterization of Indium Phosphide Quantum Dot Growth Intermediates Using MALDI-TOF Mass Spectrometry.

Clusters have been identified as important growth intermediates during group III-V quantum dot (QD) formation. Here we report a one-solvent protocol that integrates synthesis, purification, and mass characterization of indium phosphide (InP) QD growth mixtures. The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) successfully tracks the evolution of clusters and the formation of QDs throughout the synthesis. Similar clusters are observed during the formation of large particles, suggesting that these clusters serve as a reservoir for QD formation. Combining MALDI and NMR techniques further enables us to extract extinction coefficients and construct sizing curves for cluster-free InP QDs. The use of MALDI MS opens new opportunities for characterization and mechanistic studies of small-sized air-sensitive clusters or QDs.

Intact lipid imaging of mouse brain samples: MALDI, nanoparticle-laser desorption ionization, and 40keV argon cluster secondary ion mass spectrometry.

We have investigated the capability of nanoparticle-assisted laser desorption ionization mass spectrometry (NP-LDI MS), matrix-assisted laser desorption ionization (MALDI) MS, and gas cluster ion beam secondary ion mass spectrometry (GCIB SIMS) to provide maximum information available in lipid analysis and imaging of mouse brain tissue. The use of Au nanoparticles deposited as a matrix for NP-LDI MS is compared to MALDI and SIMS analysis of mouse brain tissue and allows selective detection and imaging of groups of lipid molecular ion species localizing in the white matter differently from those observed using conventional MALDI with improved imaging potential. We demonstrate that high-energy (40 keV) GCIB SIMS can act as a semi-soft ionization method to extend the useful mass range of SIMS imaging to analyze and image intact lipids in biological samples, closing the gap between conventional SIMS and MALDI techniques. The GCIB SIMS allowed the detection of more intact lipid compounds in the mouse brain compared to MALDI with regular organic matrices. The 40 keV GCIB SIMS also produced peaks observed in the NP-LDI analysis, and these peaks were strongly enhanced in intensity by exposure of the sample to trifluororacetic acid (TFA) vapor prior to analysis. These MS techniques for imaging of different types of lipids create a potential overlap and cross point that can enhance the information for imaging lipids in biological tissue sections.Graphical abstractSchematic of mass spectral imaging of a mouse brain tissue using GCIB-SIMS and MALDI techniquesElectronic supplementary materialThe online version of this article (doi:10.1007/s00216-016-9812-5) contains supplementary material, which is available to authorized users.

Application of MALDI-TOF MS for identification of clinical isolates of bacteria from humans and animals

Routinely used diagnostic methods are insufficient to identify the microorganisms with unusual biochemical properties or less commonly occurring, including zoonotic microorganisms. During our study the possibility of identification of different bacteria isolated from humans and from breeding birds using MALDI-TOF MS (Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry) and biochemical methods was compared. The material for the study were 6 reference strains from ATCC, 30 isolates selected from healthy people (throat and nasal swabs) and 16 isolates selected from birds breeding (throat swabs from the vicinity of throat of asymptomatic birds and biopsies from the heart of the dead birds). Isolates were identified based on their biochemical properties (biochemical microtests and panels for biochemical analyzer Vitek 2) or based on a protein profile using MALDI-TOF MS technique. Biochemical methods were sufficient to identify the most common and relevant to human pathology pathogens such as e.g. Escherichia coli and Staphylococcus aureus; these results were consistent with the data obtained using MALDI-TOF MS. Identification of less common bacteria required the use of MALDI-TOF MS, because some bacteria isolated from humans or breeding birds could not be classified by their biochemical properties. The biggest differences were observed in the case of bacteria from the Pasteurellaceae family, which on the basis of biochemical properties were classified mainly as Haemophilus spp., whereas in accordance to the results obtained from the protein profile as Avibacterium endocarditidis. Identification of microorganisms using MALDI-TOF MS has proved to be more useful in the diagnosis of micro-organisms rarely isolated or problematic in routine diagnostics.

MALDI MS and ICP MS Detection of a Single CE Separation Record: A Tool for Metalloproteomics

In this work, a novel approach based on off-line coupling of a single run of capillary electrophoresis (CE) separation to both matrix-assisted laser desorption/ionization (MALDI) and substrate-assisted laser desorption inductively coupled plasma (SALD ICP) mass spectrometry (MS) is presented. Using a liquid junction and subatmospheric deposition chamber, CE fractions were extracted from a separation capillary and collected as 20-nL droplets on a custom-built polyethylene terephthalate glycol (PETG) target plate coated with a 10-nm gold layer which guaranteed compatibility with both MALDI and SALD ICP techniques. The MALDI matrix solution was then added to the produced spots. After it was dried, the separation record was consecutively analyzed in MALDI MS and ICP MS instruments. Thus, both proteomic and metallomic information was obtained off-line from a single CE run. The concept was demonstrated by the analysis of a mixture of rabbit liver metallothionein isoforms. In an additional study, the droplets representing the archived separation record were alternately mixed with two different MALDI matrices to obtain complementary information on both the apoproteins and their complexes with metals from a single separation run. The presented technique is a viable alternative to online coupling of column separation to electrospray MS and nebulizer ICP MS.

Speeding up the screening of steroids in urine: Development of a user-friendly library

This work presents a novel database search engine – MLibrary – designed to assist the user in the detection and identification of androgenic anabolic steroids (AAS) and its metabolites by matrix assisted laser desorption/ionization (MALDI) and mass spectrometry-based strategies. The detection of the AAS in the samples was accomplished by searching (i) the mass spectrometric (MS) spectra against the library developed to identify possible positives and (ii) by comparison of the tandem mass spectrometric (MS/MS) spectra produced after fragmentation of the possible positives with a complete set of spectra that have previously been assigned to the software. The urinary screening for anabolic agents plays a major role in anti-doping laboratories as they represent the most abused drug class in sports. With the help of the MLibrary software application, the use of MALDI techniques for doping control is simplified and the time for evaluation and interpretation of the results is reduced. To do so, the search engine takes as input several MALDI-TOF–MS and MALDI-TOF–MS/MS spectra. It aids the researcher in an automatic mode by identifying possible positives in a single MS analysis and then confirming their presence in tandem MS analysis by comparing the experimental tandem mass spectrometric data with the database. Furthermore, the search engine can, potentially, be further expanded to other compounds in addition to AASs. The applicability of the MLibrary tool is shown through the analysis of spiked urine samples.

Physicochemical fundamentals of mass spectrometry with matrix/surface-assisted laser desorption/ionization for studies of inhibitors

The review explains the fundamentals of the methods of mass spectrometry with matrix assisted laser desorption/ionization (MALDI) and mass spectrometry with surface-assisted laser desorption/ionization (SALDI). Basics of these mass spectrometric techniques and regularities of applications of matrixes of various types are discussed. Examples of using the MALDI and SALDI techniques are presented for obtaining spectra of low-molecular compounds and compounds with a high molecular mass in connection with studies of corrosion inhibitors.

The application of atmospheric pressure matrix-assisted laser desorption/ionization to the analysis of long-term cryopreserved serum peptidome

Although most time-of-flight (TOF) mass spectrometers come equipped with vacuum matrix-assisted laser desorption/ionization (MALDI) sources, the atmospheric pressure MALDI (API–MALDI) source is an attractive option because of its ability to be coupled to a wide range of analyzers. This article describes the use of an API–MALDI source coupled to a TOF mass spectrometer for evaluation of the effects of medium- and long-term storage on peptidomic profiles of cryopreserved serum samples from healthy women. Peptides were purified using superparamagnetic beads either from fresh sera or after serum storage at −80 °C for 18 months or at −20 °C for 8 years. Data were preprocessed using newly developed bioinformatic tools and then were subjected to statistical analysis and class prediction. The analyses showed a dramatic effect of storage on the abundance of several peptides such as fibrinopeptides A and B, complement fractions, bradykinin, and clusterin, indicated by other authors as disease biomarkers. Most of these results were confirmed by shadow clustering analysis, able to classify each sample in the correct group. In addition to demonstrating the suitability of the API–MALDI technique for peptidome profiling studies, our data are of relevance for retrospective studies that involve frozen sera stored for many years in biobanks.

An efficient route towards a new branched tetrahydrofurane δ-sugar amino acid from a pyrolysis product of cellulose

(1R,5S)-1-hydroxy-3,6-dioxa-bicyclo[3.2.1]octan-2-one, is a bicyclic lactone obtained in gram-scale by catalytic pyrolysis of the renewable source cellulose. Now it has been used as a chiral building block in the preparation of the new δ-sugar amino acid, (3R,5S)-5-(aminoethyl)-3-hydroxytetrahydrofurane-3-carboxylic acid, by an efficient synthesis in five steps with a 67% overall yield. The structure of this tetrahydrofurane amino acid, isolated in protonated form, was assigned by extensive mono- and bidimensional (1)H- and (13)C-NMR analysis and mass spectrometry, including measurements by electrospray and matrix-assisted laser desorption ionization techniques, the latter one for high-resolution experiments. This amino acid is an isoster of dipeptide glycine-alanine (H-Gly-Ala-OH), with a potential use in the access of new peptidomimetics with conformationally restricted structures due to the presence of tetrahydrofurane ring. As a preliminary study in order to disclose this effect, density functional theory calculation performed in water using polar continuum model was applied to the new amino acid and H-Gly-Ala-OH dipeptide, so that to evaluate and compare the relative torsional angles for the energy-minimized structures.

Influence Factors on Particle Growth for On-line Aerosol Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry

An evaporation/condensation flow cell was developed and interfaced with the matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometer for on-line bioaerosol detection and characterization, which allows matrix addition by condensation onto the laboratory-generated bioaerosol particles. The final coated particle exiting from the condenser is then introduced into the aerodynamic particle sizer spectrometer or home-built aerosol laser time-of-flight mass spectrometer, and its aerodynamic size directly effects on the matrix-to-analyte molar ratio, which is very important for MALDI technique. In order to observe the protonated analyte molecular ion, and then determine the classification of biological aerosols, the matrix-to-analyte molar ratio must be appropriate. Four experimental parameters, including the temperature of the heated reservoir, the initial particle size, its number concentration, and the matrix material, were tested experimentally to analyze their influences on the final particle size. This technique represents an on-line system of detection that has the potential to provide rapid and reliable identification of airborne biological aerosols.

Book Review of Laser Chemistry: Spectroscopy, Dynamics and Applications

Laser Chemistry: Spectroscopy, Dynamics and Applications by Helmut H. Telle, Angel G. Ure~na, and Robert J. Donovan John Wiley & Sons, Ltd.: Chichester, West Sussex, England, 2007. 516 pp. ISBN: 978- 0471485711 (paperback). $90.00 reviewed by Benjamin A. DeGraff There is little doubt that lasers have had a profound impact on the way we do science and medicine. No science undergraduate should escape the hallowed halls without some knowledge of how these devices work and what they are good for. If you want to expand beyond the eight pages provided in traditional textbooks, you have a number of good resources from which to choose. Your choice may be dictated by how much mathematical heavy lifting you are willing to inflict on your students. At one end of the rigor spectrum is the excellent text by Silfvast, which is a must for anyone who wants to design his or her own system or work seriously in the field (1). For those whose needs are more modest, this book is a worthy candidate. This text comes close to being the complete Wikipedia of lasers and their applications. Just like Ragu spaghetti sauce, it is all in there. The first 14 chapters deal with basics: how lasers and their requisite accessories work (Chapters 3 and 4), general aspects of spectroscopy (Chapters 1, 5-9), a bit about optics and the manipulation of light (Chapters 10-12), and some things about light detection and signal processing (Chapters 13 and 14). If you crave the math, it is often available in the grayed supplemental sections. The level of writing is reasonably consistent given the book's several authors. There are numerous helpful diagrams, and the tone is clearly conceptual. The remainder of the book takes a look at various applications of lasers to modern experimentation in a number of areas. The applications selected reflect the authors' research interests and emphasize gas-phase, small-molecule systems. Thus, LIBS (laser-induced breakdown spectroscopy) and MALDI (matrixassisted laser desorption ionization) techniques are covered in a few pages, while high-resolution, zero-kinetic energy photoelectron spectroscopy has more extensive coverage. That is OK, because the authors wrote the book and therefore got to choose which applications to present. While the hazards of any applications chapter is the obsolescence of the papers cited, most of the material is sufficiently basic that students can still get a good feel for the area even if the reference list ages. Specifically, Chapters 15-18 deal with small-molecule photochemistry as elucidated by laser techniques. The scene then shifts in Chapters 20-23 to various techniques to probe reacting systems, again gas phase. There are chapters on probing the adsorbed state and surface chemistry (Chapters 26 and 27), as well as studies on various complexes (Chapter 24). The last three chapters give a brief overview of some analytical, environmental, and medical applications. The book comes complete with warts, but none are deal breakers. The authors use two sets of references, a specific set and a general set, which can be a bit confusing. Apparently the publisher wanted to see whether the book would make The New York Times' bestseller list before investing in color, but that is not the authors' fault. The most significant problem is the promised Web site with supplemental material and problems to support the book (2). As of thiswriting, the site is not fully operational and only a limited amount of material is available. This is unfortunate for those like this reviewer who might like to use this book as the main text in a special topics class. Overall, this is a worthy addition to the laser literature and well suited for undergraduate use. At this point, I would give it a B, but that may well rise to an A- if the Web site finally comes online. The book sells for about $90, but is available for less from discount vendors. For students, this is a real bargain. I'm glad I have a copy, and I will make use of it in my laser course this semester.

Mass Spectrometry-Based Approaches for Structural Studies on Protein Complexes at Low-Resolution

Almost two decades after the introduction of the electrospray ionization (ESI) and the matrix-assisted laser desorption ionization (MALDI) techniques, mass spectrometry (MS) has become a key technology in the emerging field of proteomics. MS-based procedures combined with various affinity-trapping methods allowed massive identification of constitutive elements in multi-protein complexes from different organisms. Similarly, various MS-based strategies have been developed and applied to low-resolution structural studies on protein and protein complex. In fact, products generated either by limited proteolysis, selective chemical modification or radical probe reactions performed on isolated proteins have been characterized by ESI and MALDI techniques, providing information on the location of residues accessible on molecular surface. Differential experiments performed before and following complex formation allowed the identification of masked regions in each component of the complex after binding, generated as a result of macromolecular interaction. Similarly, MS analysis of protein complex cross-linking products has led to the identification of spatially closed amino acids occurring at molecular interface. Nowadays, these methodologies are used for experimental validation of insilico generated models and verification of interface regions predicted by bioinformatics computations. Accordingly, these approaches present a fundamental resource when severe limitations using high-resolution methods, such as X-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy, which arise from the amount of sample required, difficulties in crystallization or solubilization, may hinder a definitive structural characterization. In this review, the combined use of chemical cross-linking, limited proteolysis, selective chemical modification or radical probe reactions with MS analysis is reviewed and discussed in the point of view of structural biology studies on protein and protein complexes. Keywords: Protein complex, protein interaction, cross-linking, limited proteolysis, selective chemical modification, radical probe, molecular modelling

Matrix-free Laser Desorption/Ionization on Vertically Aligned Carbon Nanotube Arrays

The matrix-assisted laser desorption/ionization (MALDI) has established its position as one of the most useful ionization techniques in mass spectrometry and its contribution to the scientific communities related to mass spectrometry was appreciated with the 2002 Nobel Prize in Chemistry given to the first developer, Tanaka. It is really an effective and sensitive ion formation technique which commonly employs an organic acid as the matrix. The use of such organic acids as the matrices has provided the high efficiency of desorption and ionization of large molecules including peptides, proteins, synthetic polymers, etc. for the MALDI technique. Interestingly, the matrix, which made the MALDI technique practical, poses an intrinsic constraint to the analyses of relatively small molecules below 1000 Da because the low mass regions in MALDI mass spectra are dominated by the strong background signals of the matrix molecule, its dimer, and their clusters with solvent molecules. Several approaches have been tried to find the methods that give the high desorption/ionization efficiency of MALDI without using the organic matrices. Probably the most successful matrix-free laser desorption/ ionization technique must be the use of porous silicon as a replacement of the matrix. The desorption/ionization on porous silicon(abbreviated as DIOS) was found to be highly sensitive for the sample below 3,000 Da and showed no interference at all in this low mass region, and is now commercially available. Although the DIOS has been very successful, it has a non-negligible shortcoming that its performance deteriorates with time after fabrication. The degradation may be slowed down by derivatization of the surface but cannot be completely eliminated. In this Note, we report that the vertically grown carbon nanotube arrays may be used as a substrate for matrix-free laser desorption/ionization of relatively small molecules. It turned out to be highly sensitive for small peptides near and below 2,000 Da and its ionization efficiency does not change after a long-time storage in the room atmosphere.

Matrix-Assisted Laser Desorption/Ionization, Time of Flight, and Angiotensin II

Elsewhere in this issue, Jankowski et al show that mononuclear cells produce sufficient angiotensin II (Ang II) to stimulate Ang II type 1 receptors.1 That finding alone is noteworthy; however, my attention was riveted by the methods the authors used to measure Ang II. Ang II is generally measured by radioimmunoassay. Because of antibody specificity, the samples are first purified by high-performance liquid chromatography (HPLC). The assay is difficult, tedious, and fraught with pitfalls. The sample collections, standardization of collection conditions, and use of appropriate inhibitors are only some of the problems. Only a few investigators do this assay well. An alternative, more accurate, method would be most welcome. Were the method sufficiently established, and were the method routinely available, direct Ang II measurements could be of great clinical utility. After reading the article and meeting with the senior author, I hedge the hope that matrix-assisted laser desorption/ionization (MALDI)–time of flight (TOF) might bring this wish to reality. Jankowski et al adapted MALDI-TOF to measure Ang II or other small peptides and proteins with interesting biological activities in a previous study.2 In their article, they outlined a MALDI-TOF–based strategy to screen protein fractions for defined enzymatic activities. The authors prepared porcine kidney extracts that were then immobilized by covalent coupling to activated affinity beads. The immobilized proteins were incubated with probes …

Lipid imaging by gold cluster time-of-flight secondary ion mass spectrometry: application to Duchenne muscular dystrophy

Imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) has expanded very rapidly with the development of gold cluster ion sources (Au(3+)). It is now possible to acquire ion density maps (ion images) on a tissue section without any treatment and with a lateral resolution of few micrometers. In this article, we have taken advantage of this technique to study the degeneration/regeneration process in muscles of a Duchenne muscular dystrophy model mouse. Specific distribution of different lipid classes (fatty acids, triglycerides, phospholipids, tocopherol, coenzyme Q9, and cholesterol) allows us to distinguish three different regions on a mouse leg section: one is destroyed, another is degenerating (oxidative stress and deregulation of the phosphoinositol cycle), and the last one is stable. TOF-SIMS imaging shows the ability to localize directly on a tissue section a great number of lipid compounds that reflect the state of the cellular metabolism.