Monday, March 11, 2013

Introducing flowprobe Mass Spectrometry

Prosolia annouces the flowprobe, a real-time coninuous flow microextraction technique for mass spectrometry surface analysis.  The flowprobe was designed with the researcher in mind, combining the advantages of continuous flow microextraction and electrospray ionization for sustained, spatially resolved sampling and gentle mass spectrometric analysis in an efficient and automated format. Flowprobe’s continuous solvent flow generates the highest extraction efficiency ambient sampling technology commercially available. Amenable to spot sampling and imaging a range of surfaces--from cells and tissues to analytic/polymeric substrates—it can accelerate drug distribution studies, cancer and microorganism profiling, and biochemical analyses.

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Saturday, February 2, 2013

Fast Phenotyping of LFS- Silenced (Tearless) Onions by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS)

Fast MS techniques have been applied to the analysis of sulfur volatiles in Allium species and varieties to distinguish phenotypes. Headspace sampling by proton transfer reaction (PTR) MS and surface sampling by desorption electrospray ionization (DESI) MS were used to distinguish lachrymatory factor synthase (LFS)-silenced (tearless; LFS-) onions from normal, LFS active (tear-inducing; LFS+), onions. PTR-MS showed lower concentrations of the lachrymatory factor (LF, 3) and dipropyl disulfide 12 from tearless onions. DESI-MS of the tearless onions confirmed the decreased LF 3, and revealed much higher concentrations of the sulfenic acid condensates. Using DESI-MS with MS2 could distinguish zwiebelane ions from thiosulfinate ions. DESI-MS gave reliable fast phenotyping of LFS+ versus LFS- onions by simply scratching leaves and recording the extractable ions for <0.5 min. DESI-MS leaf compound profiles also allowed the rapid distinction of a variety of Allium cultivars to aid plant breeding selections.

DOI: 10.1021/jf304444s

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Wednesday, January 30, 2013

Rapid screening of synthetic cathinones as trace residues and in authentic seizures using a portable mass spectrometer equipped with desorption electrospray ionization

Coupling DESI-MS with portable instrumentation allowed sensitive and selective examination of synthetic cathinones from various substrates, in complex mixtures, and directly from mock and authentic forensic evidence. This instrumental method has the potential to assess the evidentiary value of forensic samples at crime scenes, reducing backlogs and expediting criminal investigations.

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Sunday, January 6, 2013

Desorption Electrospray Ionization Imaging Mass Spectrometry as a Tool for Investigating Model Prebiotic Reactions on Mineral Surfaces

By Fernandez et al.

Mineral-assisted thermal decomposition of formamide (HCONH2) is a heavily studied model prebiotic reaction that has offered valuable insights into the plausible pathways leading to the chemical building blocks of primordial informational polymers. To date, most efforts have focused on the analysis of formamide reaction products released in solution, although several studies have examined the role of mineral catalysts in promoting this chemistry. We show here that the direct investigation of reactive mineral surfaces by desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) gives a new perspective on the important role of the mineral surface in the formation of reaction products. As a proof-of-principle example, we show that DESI-MSI allows interrogation of the molecular products produced on heterogeneous granite samples with minimal sample preparation. Purine and pyrimidine nucleobases and their derivatives are successfully detected by DESI-MSI, with a strong correlation of the spatial product distribution with the mineral micro-environment. To our knowledge, this study is the first application of DESI-MSI to the study of complex and porous mineral surfaces, and their roles in chemical evolution. This DESI-MSI approach is generally applicable to a wide range of reactions or other processes involving minerals.

Sunday, December 23, 2012

229 rapid, untargeted lipid determination in individual bovine oocytes and pre-implantation embryos by high-resolution desorption electrospray ionization mass spectrometry.

Lipid structural analysis in individual pre-implantation mammalian embryos is hampered by the small amount of biological material, such that most studies use staining methods or gas chromatography analysis generate information only on the fatty acyl residues. Recent developments in high-resolution desorption electrospray ionization mass spectrometry (DESI-MS) allow the analysis of free fatty acids (FA) and glycerophospholipids (PL) in individual bovine embryos. Here, we report on the use of DESI-MS for the sensitive analysis of triacylglycerol (TAG) species, profiles of FA and PL in individual bovine oocytes and embryos. Bovine oocytes (n=40) and blastocysts (n=42) were frozen in a minimal volume of PBS (2 to 5µL). Samples were directly deposited on glass slides after thawing. After drying, a volume of 500µL of methanol:water (1:1, vol/vol) was carefully deposited on the surface of the glass slide and removed by orienting the glass slide vertically to eliminate PBS salts. An Orbitrap mass spectrometer was used for the experiments. Parameters for the positive ion mode were as follows: acetonitrile (ACN) supplemented with 3µLmL(-1) of AgNO(3) at a 5µLmin(-1) flow rate, injection time of 1000ms, and a mass-to-charge range of m/z 400 to 1500. For the negative ion mode, the solvent combination used was acetonitrile+dimethylformamide (1:1, vol/vol) at a 1.0µLmin(-1) flow rate, a maximum injection time of 1000ms, and a mass-to-charge range of m/z 150 to 1000. Positive ion mode data for the detection of TAG species were acquired first, followed by acquisition of FA and PL in the negative ion mode. Detection of TAG by DESI, which is extremely useful for bovine embryo cryopreservation and metabolism research, has been performed by adding AgNO(3) in the DESI spray to obtain silver adducts, which are easily recognised by the characteristic 1:1 abundance ratio of the 107:109 Ag isotopes. The most abundant fatty acyl residues present in TAG species were palmitic (P), linoleic (L), oleic (O), and stearic (S) acids, such as TAG of m/z 937, PPL (50:2); m/z 965, POO (52:1); m/z 967, POS (52:2); m/z 989, OOL/LLS (54:4); and m/z 991, OOO, SOL (54:3). Free FA and PL profiles collected from the same samples in the negative ion mode were similar to those in our recent report (2012 J. Mass Spectrom. 47, 29-33). Lipid attribution has been performed based on high-resolution mass analysis. Multivariate statistics from this data set will allow visualisation of differences observed in the lipid profiles among samples. In conclusion, we report the use of DESI-MS for the sensitive analysis of TAG in individual bovine oocytes and embryos and the creation of profiles of FA, PL, and TAG species in the same sample by DESI-MS.

Source: PubMED

Thursday, December 20, 2012

Protein structure evolution in liquid DESI as revealed by selective noncovalent adduct protein probing


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Previous experiments based on charge state distributions have suggested that liquid desorption electrospray ionization (DESI) is capable of preserving solution phase protein structure during transfer to the gas phase (Journal of the American Society for Mass Spectrometry 21 (2010) 1730–1736). In order to examine this possibility more carefully, we have utilized selective non-covalent adduct protein probing (SNAPP) to evaluate protein structural evolution in both liquid DESI and standard ESI under a variety of conditions. Experiments with cytochrome c (Cytc) demonstrated that methanol induced conformational shifts previously observed with ESI are also easily observed with liquid DESI. However, undesirable acid-induced unfolding becomes apparent at very high concentrations of methanol in liquid DESI due to acetic acid in the spray solvent, suggesting that there are conditions under which liquid DESI will not preserve solution phase structure. The effects of ammonium acetate buffer on liquid DESI SNAPP experiments were examined by monitoring structural changes in myoglobin. Heme retention and SNAPP distributions were both preserved better in liquid DESI than traditional ESI, suggesting superior performance for liquid DESI in buffered conditions. Finally, liquid DESI SNAPP was used to study the natively disordered proteins α, β, and γ synuclein with SNAPP. α-Synuclein, the main component of fibrils found in patients with Parkinson's disease, yielded a significantly different SNAPP distribution compared to β and γ synuclein. This difference is indicative of highly accessible protonated basic side chains, a property known to promote fibril formation in proteins.