Spray solvent doped with silver ions increases the ease of olefin detection by desorption electrospray ionization (DESI). Characteristic silver adducts were generated in up to 50 times greater abundance when compared to conventional DESI spray solvents for the biologically significant olefin, arachidonic acid, in the positive ion mode. In the analysis of 26 lipids, silver adduct formation was highly favorable for fatty acids, fatty acid esters and prostaglandins but not applicable to some other classes (e.g., polar lipids such as ceramide and its derivative cerebroside sulfate). An investigation exploring competitive Ag(+) cationization with a mixture of components demonstrated that polyunsaturated compounds form Ag(+) adducts most readily. Silver cationization allowed the distinction between three sets of isomers in the course of multiple-stage collision-induced dissociation, so providing insight into the location of the olefin bonds. A silver ion-doped solvent was used in DESI imaging of normal and tumor canine bladder tissue sections. The Ag(+) fatty acid adducts permitted post facto differentiation between the normal and tumor regions. In addition, silver adduct formation in the course of DESI imaging of tissue sections revealed the presence of triacylglycerides, a class of compounds not previously identified through DESI imaging. A simple silver nitrate spray solvent has the potential to further improve DESI analysis of unsaturated biomolecules and other molecules containing π-bonds through selective silver cationization.

Reaction monitoring using inductive ESI mass spectrometry allows chemical reactions to be tracked in real time, including air- and moisture-sensitive as well as heterogeneous reactions. Highly concentrated solutions can also be monitored for long periods without emitter clogging. Sheath gas assists in nebulization and a sample splitter reduces the delay time and minimizes contamination of the instrument. Short-lived intermediates (ca. 5 s) were observed in Pd/C-catalyzed hydrogenolysis, and several intermediates were seen in Negishi cross-coupling reactions.

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Ambient ionization methods such as desorption electrospray ionization (DESI) allow the analysis of chemicals adsorbed at surfaces without the need for sample (or surface) pretreatment. A limitation of current implementations of these ionization sources is the small size of the area that can be sampled. This makes examination of surfaces of large areas time-consuming because of the need to raster across the surface. This paper describes a DESI source that produces a spray plume with an effective desorption/ionization area of 3.6 cm(2), some 200 times larger than given by conventional DESI sources. Rhodamine 6G and several drugs of abuse (codeine, heroin and diazepam) were used to demonstrate the ability to use large-area DESI MS to perform rapid (a few seconds) representative sampling of areas of the order of several square centimetres without scanning the probe across the surface. The large area ion source displayed high sensitivity (limits of detection in the high nanogram range) and high reproducibility (approximately 20 to 35% relative standard deviation). The rapid analysis of even larger surfaces (hundreds of cm(2)) for traces of explosives is possible using a sorbent surface wipe followed by large-area DESI interrogation performed directly on the wipe material. The performance of this mass transfer dry wipe method was examined by determination of the limits of detection of several explosives. Surfaces with different topographies and compositions were also tested. Using this method, absolute limits of detection observed for HMX and RDX from plastic surfaces and skin were found to be as low as 10 ng cm(-2). The concentration of residue from large surface areas in this technique allowed the detection of 100 ng of explosives from surfaces with areas ranging from 1.00 x 10(3) cm(2) to 1.40 x 10(4) cm(2).

, or Cs ϩ therefore represent a new type of cluster ion that is homochiral in its internal subunits, which then assemble in a random fashion to form octamers. We tentatively interpret the homochirality of these tetramers as a consequence of assembly of the serine molecules around a central metal ion. The data provide additional evidence that the neutral serine octamer is homochiral and is readily cationized by smaller ions. (J Am Soc Mass Spectrom 2007, 18, 856 -868) © 2007 American Society for Mass Spectrometry C ations of the alkali metals, especially Na ϩ and K ϩ , are involved in a wide variety of biological processes. To take just one example, they participate in the stabilization of noncovalently bound complexes of biological macromolecules in living organisms. In particular, telomeric DNA found at the ends of chromosomes is stabilized by forming multistrand complexes, known as G-quadruplexes, which are held together by hydrogen bonds and further stabilized by the incorporation of alkali metal cations into cavities in their structures [1][2][3]. Mass spectrometry [1], nuclear magnetic resonance, X-ray crystallography and other spectroscopic techniques have shown that small biomolecules can also form relatively stable clusters with alkali metal cations. Examples include nucleobases [4 -6] and nucleosides (as well as their derivatives) [7][8][9], and amino acids [10,11]. A particular feature of alkali metal adducts of small molecular clusters is that they often have a net positive charge and can be characterized by mass spectrometry, a technology that has proven to be key in many studies of clusters [11][12][13][14][15][16][17][18][19].Electrospray ionization (ESI) [20,21] is a versatile ionization technique, which allows biological macromolecules, fragile noncovalently bound complexes [22][23][24][25][26], and other fragile nonvolatile species to be easily transferred from solution into the gas-phase, where mass spectral data can be obtained on the resulting ions. Although the possibility exists of conformational rearrangement [27,28] and other structural changes during the ESI process, there is overwhelming evidence that electrospray ionization is successful in the characterization of solution-phase species via a study of the corresponding gas-phase ions [24,26]. Spray ionization methods derived from the original ESI method include sonic spray ionization (SSI) [29,30] and cold spray ionization (CSI) [31,32]. Recently, electrosonic spray ionization (ESSI) [33,34], a combination of ESI and SSI, was introduced. This particular spray ionization method is very gentle, yet readily yields fully desolvated ions [33,34]. The variant methods SSI, CSI, and ESSI are all believed to provide gentler ionization than normal electrospray, allowing labile species that exist in solution to survive the ionization process as well as being applicable to nonvolatile analytes.The droplet evaporation process in the gentle variant methods on ESI can lead to even more aggregation than occurs in ESI itself. This tendency has been fo...

A recently developed hand-held, rectilinear ion trap mass spectrometer, capable of performing in situ analysis, has been evaluated for a variety of environmentally relevant analytes. Different sampling and ionization methods were implemented, demonstrating the considerable versatility of this instrument. A discontinuous (viz. pulsed) atmospheric pressure inlet (DAPI) was used to introduce externally-generated analyte ions. Nitro compounds were ionized by electrosonic spray ionization (ESSI) yielding the protonated and sodiated forms of the molecular ion, as well as fragment ions. The amines 2,2,6,6-tetramethylpiperidine, triethylamine and 2,6-diphenylpyridine showed low parts per billion (ppb) detection limits. Vapor phase external ionization was used to examine the chemical warfare simulant dimethyl methylphosphonate and the insect repellant N,N-diethyl-m-toluamide. Membrane introduction mass spectrometry (MIMS) was used as the introduction system for hydrophobic analytes using a selectively permeable (polydimethylsiloxane) membrane placed within the vacuum manifold with subsequent ionization of the thermally desorbed neutral compounds inside the ion trap. MIMS allowed the quantitation of trace levels (a few ppb) of fluorinated compounds in the vapor phase. MIMS was also applied to the quantitation of aqueous polycyclic aromatic hydrocarbons (PAH's) with limits of detection again in the low ppb range for naphthalene, acenaphthene, anthracene and phenanthrene.

A miniature ion trap mass analyzer was applied to the analysis of traces of hydrocarbons and simple heteroatomics in the vapor phase and in aqueous solution. Vapors of acetone, acetic acid, acetonitrile, benzene, butanethiol, carbon disulfide, hexane, dichloromethane, naphthalene, toluene and xylenes were detected and quantified using solid sorbent trapping and, in some cases, by passage through a membrane interface. Aqueous solutions of benzene, toluene, xylenes, hexane and a petroleum naphtha distillate were examined using the membrane interface. Sampling, detection and identification of all compounds was completed in times of less than one minute. The gas-phase samples of toluene and benzene were detected at 200 ppt (limit of detection, LOD) for toluene and 600 ppt for benzene. Identification of benzene and xylene in aqueous solutions was readily achieved with LODs of 200 and 400 ppb, respectively. Quantification over a linear dynamic range of two orders of magnitude for the aqueous samples and three orders of magnitude for the vapor-phase samples was demonstrated.

Abstract:© Versita Sp. z o.o. Received 9 March 2011; Accepted 24 May 2011 Keywords: Perchlorate and chlorate ions • DESI MS • Ambient ionization methods • Oxidants • ExplosivesDesorption electrospray ionization (DESI), an established ambient ionization method in mass spectrometry (MS) for the analysis of organic compounds, is applied here to trace detection of inorganic salts, including inorganic oxidants. In-situ surface analysis of targeted compounds, including nitrogen-, halogen-and sulfur-salts, down to sub-nanogram levels, was performed using DESI-MS. Successful experiments were carried out in both the negative and the positive ion modes; simple anions and cations as well as small cluster ions were observed. Various surfaces are examined and surface porosity effects were briefly explored. Absolute detection limits on porous polytetrafluoroethylene (PTFE) of 120 pg (surface concentration 0.07 ng mm ), were achieved for sodium chlorate and sodium perchlorate, respectively. The compounds of interest were examined in the presence of a hydrocarbon mixture to assess matrix effects: only a two-or three-fold decrease in the target ion intensity was observed. Commercial fireworks were analyzed to determine perchlorate salts in complex mixtures. This work demonstrates the potential applicability of ambient ionization mass spectrometry to forensic investigations involving improvised explosives.