Silver nanoparticle functionalized glass fibers for combined surface-enhanced Raman scattering spectroscopy (SERS)/surface-assisted laser desorption/ionization (SALDI) mass spectrometry via plasmonic/thermal hot spots.

We presented the fabrication of a silver nanoparticle (Ag NP) functionalized glass fiber (Ag-GF) substrate for combined surface-enhanced Raman scattering spectroscopy (SERS)/surface-assisted laser desorption/ionization (SALDI) mass spectrometry. Ag NPs were immobilized onto the surface of glass fibers through a simple sputter deposition process. The SERS and SALDI activities strongly depended on the nanostructures of the deposited Ag NPs on the GFs. The closely-packed Ag NPs with a size of 20-50 nm and an inter-particle nanoscale gap of less than 10 nm were effective for the simultaneously enhanced SERS/SALDI substrate via plasmonic/thermal "hot spots", while the interconnected continuous Ag film reduced both the SERS/SALDI activities. The SERS enhanced factor (EFSERS) and SALDI enhanced factor (EFSALDI) were newly proposed. Finally, the concentration-dependent signal intensities of SERS and SALD-MS of sulfur compounds using an identical Ag NP-GF substrate were examined, and the linear dependence relationship in the log-log plot was demonstrated for the combined quantitative SERS/SALDI-MS analysis.

2-Hydrazinoquinoline: a reactive matrix for matrix-assisted laser desorption/ionization mass spectrometry to detect gaseous carbonyl compounds.

The sensitivity, range of applications, and reaction mechanism of 2-hydrazinoquinoline as a reactive matrix for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) were examined. Using a reaction chamber (125L) equipped with a stirring fan and a window for moving the MALDI-MS plate and volatile samples in and out, the sensitivities of 2-hydrazinoquinoline to gaseous aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and n-butyraldehyde) and ketones (acetone, methyl ethyl ketone, and methyl isobutyl ketone) were determined to be at least parts per million (ppm) levels. On the other hand, carboxylic acids (formic acid, acetic acid, propionic acid, and butyric acid) and esters (ethyl acetate, pentyl acetate, isoamyl acetate, and methyl salicylate) could not be detected by 2-hydrazinoquinoline in MALDI-MS. In addition to 2,4-dinitrophenylhydrazine, a common derivatization reagent for analyzing carbonyl compounds quantitatively in gas chromatography and liquid chromatography, the dissolution of 2-hydrazinoquinoline in an acidic solution, such as trifluoroacetic acid, was essential for its function as a reactive matrix for MALDI- MS.

Correction: Imaging mass spectrometry of a mouse brain by tapping-mode scanning probe electrospray ionization.

Correction for 'Imaging mass spectrometry of a mouse brain by tapping-mode scanning probe electrospray ionization' by Yoichi Otsuka et al., Analyst, 2014, 139, 2336-2341.

Imaging mass spectrometry of a mouse brain by tapping-mode scanning probe electrospray ionization.

Methods for ambient sampling and ionization enable chemical information to be obtained with minimal sample preparation. Also, imaging mass spectrometry (IMS) enables the spatial distribution of multiple components to be determined by a single measurement. Here, we report an improved method of tapping-mode scanning probe electrospray ionization (t-SPESI) for ambient sampling and ionization in which probe oscillation is stabilized by using a piezo actuator. We demonstrate negative-mode IMS of a mouse coronal brain section and show that, compared with desorption electrospray ionization, t-SPESI provides unique features in the mass spectra: signal enhancement of fatty acid and lipids, and formation of multivalent ions tentatively assigned to gangliosides. These results would indicate the capability for the generation of multiple types of ions with t-SPESI.

Use of high-resolution mass spectrometry to identify precursors and biodegradation products of perfluorinated and polyfluorinated compounds in end-user products.

Structural identification of perfluoroalkyl and polyfluoroalkyl substances found in end-user products and their biodegradation products was performed using ultra-high resolution mass spectrometry. Little attention has so far been paid to the environmental burden of perfluorooctane sulfonate and perfluorooctanoic acid from compounds with a molar mass of ~2,000. Analysis of end-user waterproofing and stain repellent products revealed the presence of numerous ions with molar masses ranging from 1,000 to 2,000 and complex mass spectra. Ultra-high resolution mass spectrometry determined the accurate mass of the observed ions, allowing the cleavage position and fragment structure to be determined. The precursor structures were determined based on reconstitution of the retrieved fragments. Products of fluorochemical manufacturers before voluntary regulation comprised compounds with plural perfluorooctyl chains. In the current product lines, compounds comprising perfluorobutyl chains were detected. Biodegradation tests using activated sludge revealed that biodegradation products consistent with those reported previously were generated even from complex end-user products. For example, the biodegradation test revealed the formation of N-ethyl perfluorooctane sulfonamido acetic acid and various fluorotelomer acids in the samples. The results of the present study suggest that the environmental burden of these compounds should be reevaluated.

Electrochemical reactions of lithium-sulfur batteries: an analytical study using the organic conversion technique.

This investigation elucidates the electrochemical reaction process occurring within lithium-sulfur battery cells in detail, which has been unclear even after a half century of study primarily due to the very high reactivity of the polysulfide species. The polysulfide intermediates were deactivated by organic conversion - benzylization, and LC/MS and NMR analyses were first applied. The results demonstrate that the second voltage plateau in the discharge profile, which is the most important step in practical use because of its constant voltage, is dominated by the reduction of the Li2S3 intermediate. The first voltage plateau and the transition state between the plateaus, in which the voltage varies with the capacity, are associated with multiple reactions including the decomposition of S8 into Li2Sx (x = 1 to 7) and the transformation of Li2Sy (y = 4 to 8) into Li2Sz (z = 1 to 3). It is also revealed that longer polysulfide species, Li2Si (i = 6 to 8), are responsible for the redox shuttle phenomenon, which causes serious capacity degradation.

Suitability of GaP nanoparticles as a surface-assisted laser desorption/ionization mass spectroscopy inorganic matrix and their soft ionization ability.

Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) using GaP nanoparticles (NPs) prepared by a gas evaporation method was investigated on poly(ethylene glycol)s (PEGs). The mass spectra of PEG and survival yield measurements suggested that larger GaP NPs have a quite high soft ionization ability.

A thiophene-containing compound as a matrix for matrix-assisted laser desorption/ ionization mass spectrometry and the electrical conductivity of matrix crystals.

The electrical conductivity of the matrix crystal might be a new factor to enhance matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) sensitivity. In MALDI-MS, several compounds are used as a standard matrix. Utilization of such compounds is based on an a posteriori approach, but there is no theoretical guidance for selecting a matrix. In an attempt to further understand performance in MALDI-MS, we utilized peptide detection for random screening of a chemical library (12,383 compounds) for compounds with matrix functions in MALDI-MS. A lot of thiophene compounds were found to be a matrix, in which 2-[5-(2,4-dichlorobenzoyl)-2-thienyl] acetic acid (DCBTA) provided an important clue to measure the electrical conductivity of the matrix crystal, because the structure of DCBTA is analogous to conductive polymers and organic solar cells. Most of the crystals of standard matrices, such as alpha-cyano-4-hydroxycinnamic acid (CHCA), 3,5-dimethoxy-4-hydroxycinnamic acid [sinapinic acid, (SA)], and DCBTA showed electrical conductivity, whereas the conductivity of crystal was not observed in 2,5-dihydroxybenzoic acid (2,5-DHB). On the other hand, super-DHB using 2-hydroxy-5-methoxybenzoic acid [5-methoxysalicylic acid, (MSA)] as an additive to 2,5-DHB, improved the electrical conductivity of the crystal, that followed the enhancement of peak intensity in MS spectrum. These observations might indicate that the electrical conductivity of matrix crystals is a key consideration in obtaining efficient MALDI performance.

Functionalized graphene-coated cobalt nanoparticles for highly efficient surface-assisted laser desorption/ionization mass spectrometry analysis.

Graphene-coated cobalt nanoparticles surface-functionalized with benzylamine groups (CoC-NH(2) nanomagnets) were shown to effectively enrich analytes for surface-assisted laser desorption/ionization mass spectrometry (affinity SALDI-MS) analysis. These CoC-NH(2) nanomagnets are highly suited for use with affinity SALDI-MS because their mean diameter of 30 nm, high specific surface area of 15 m(2) g(-1), and high-strength saturation magnetization of 158 emu g(-1) led to efficient extraction of analytes by magnetic separation, which in turn enabled excellent SALDI-MS performance. Surface modification of CoC nanomagnets with benzylamine groups increased the yield of peptide ions and decreased fragmentation of benzylpyridinium ions, so-called "thermometer ions" formed through soft ionization. The CoC-NH(2) nanomagnets were used to extract perfluorooctanesulfonate from large volumes of aqueous solutions by magnetic separation, which was identified directly by SALDI-MS analysis with high sensitivity even at the sub-part-per-trillion level (∼0.1 ng/L). The applicability of CoC-NH(2) nanomagnets in conjunction with SALDI-MS for the enrichment and detection of pentachlorophenol, bisphenol A, and polyfluorinated compounds (PFCs) with varying chain length, which are environmentally significant compounds, as well as small drugs, was also evaluated.

Hydroxy-amide functionalized azolium salts for Cu-catalyzed asymmetric conjugate addition: stereocontrol based on ligand structure and copper precatalyst.

A series of hydroxy-amide functionalized azolium salts have been designed and synthesized for Cu-catalyzed asymmetric conjugate addition reaction. The (CH(2))(2)-bridged hydroxy-amide functionalized azolium ligand precursors 2, in addition to the previously reported CH(2)-bridged azolium salts 1, have been prepared from readily available enantiopure ß-amino alcohols. The combination of a Cu species with 1 or 2 efficiently promoted the 1,4-addition reaction of cyclic enones with dialkylzincs. For example, the reaction of 2-cyclohepten-1-one (17) with Bu(2)Zn in the presence of catalytic amounts of Cu(OTf)(2) and 1 gave (S)-3-butylcycloheptanone (20) in 99% yield and 96% ee. On the other hand, when the reaction was carried out under the influence of Cu(OTf)(2) combined with 2, (R)-20 in preference to (S)-20 was obtained in 98% yield and 80% ee. In this manner, the enantioselecvity was switched by controlling the structure of chiral ligand. Additionally, the reversal of enantioselectivity was also achieved by changing the Cu precatalyst from Cu(OTf)(2) to Cu(acac)(2) with the same ligand. The combination of Cu(acac)(2) with CH(2)-bridged azolium salt 1 in the reaction of 17 with Bu(2)Zn led to formation of (R)-20 as a major product in 55% yield and 80% ee. This result was in contrast to the Cu(OTf)(2)/1 catalytic system, where the 1,4-adduct with opposite configuration was obtained. Moreover, use of the Cu(acac)(2)/2 catalytic system produced (S)-20, while (R)-20 was formed by the Cu(OTf)(2)/2 catalytic system. Thus, it was found that either varying the linker of the chiral ligands or changing the counterion of Cu species between a OTf and acac ligand initially on the metal led to dual enantioselective control in the 1,4-addition reaction.

Platinum vapor deposition surface-assisted laser desorption/ionization for imaging mass spectrometry of small molecules.

RATIONALE: Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) allows for the simultaneous detection and imaging of several molecules in a sample. However, when using an organic matrix in the MALDI-IMS of small molecules, inhomogeneous matrix crystallization may yield poorly reproducible peaks in the mass spectra. We describe a solvent-free approach that employs a homogeneously deposited metal nanoparticle layer (or film) for small-molecule detection. METHODS: Platinum vapor deposition surface-assisted laser desorption/ionization imaging mass spectrometry (Pt vapor deposition SALDI-IMS) of small molecules was performed as a solvent-free and organic-matrix-free method. A commercially available magnetron sputtering device was used for Pt deposition. Vapor deposition of Pt produced a homogenous layer of nanoparticles over the surface of the target imaging sample. RESULTS: The effectiveness of Pt vapor deposition SALDI-IMS was demonstrated for the direct detection of small analytes of inkjet ink on printed paper as well as for various other analytes (saccharides, pigments, and drugs) separated by thin-layer chromatography (TLC), without the need for extraction or concentration processes. The advantage of choosing Pt instead of Au in SALDI-IMS was also shown. CONCLUSIONS: A solvent-free approach involving the direct deposition of Pt on samples (SALDI-IMS) is effective for the analysis of inkjet-printed papers and various analytes separated by TLC. This method would be useful in imaging analyses of various insulating materials such as polymers and biological materials.

Scanning probe electrospray ionization for ambient mass spectrometry.

RATIONALE: Ambient sampling and ionization techniques have been attracting attention in imaging mass spectrometry because they offer the advantage of rapid testing. We have developed a method which exploits the fluid motion of charged solvents for both local sampling and ionization with a single vibrating capillary probe. METHODS: The capillary probe was used to supply solvents in order to form a liquid bridge between the probe and a sample surface. A bias voltage was applied to the solvents to generate electrospray ionization (ESI). The probe was also vibrated by either an ultrasonic transducer fixed at the back of the sample (contact-mode) or spontaneous vibration of probe itself (tapping-mode). The ions generated by ESI were detected by a triple quadrupole mass spectrometer. RESULTS: Sampling of the specimens at the liquid bridge and ESI of the dissolved solutions both occurred around the probe apex. The sampling and ionization co-existed in contact-mode, while they were explicitly separated in the tapping-mode. The one-dimensional mapping of solid samples such as protein films and tissue sections was demonstrated. The results indicated that there was little cross-contamination during the operation. CONCLUSIONS: The method, named scanning probe electrospray ionization (SPESI), promises to be a simple and unique approach toward direct sampling and ionization methodology.

Cytotoxic prodigiosin family pigments from Pseudoalteromonas sp. 1020R isolated from the Pacific coast of Japan.

Pseudoalteromonas sp. 1020R, isolated from the Pacific coast of Japan, produces prodigiosin family pigments. Structural analysis indicated that these are prodigiosin (2-methyl-3-pentyl-prodiginine) and three other prodigiosin congeners which differ only in the lengths of the alkyl side chains. These compounds exhibited different extents of cytotoxicity against U937 leukemia cells, and cell death was accompanied by typical features of apoptosis.

Evaluation of river pollution of neonicotinoids in Osaka City (Japan) by LC/MS with dopant-assisted photoionisation.

An atmospheric pressure photoionisation (APPI) source for liquid chromatography/mass spectrometry (LC/MS) was applied to determine neonicotinoid pesticides in the aquatic environment. Dopant-assisted APPI was very effective in the ionisation of neonicotinoids. Neonicotinoids generated protonated molecules in APPI with high sensitivity, while adduct ions, such as sodiated molecules, were predominantly generated in conventional electrospray ionisation. The ionisation of neonicotinoids was confirmed by ultra-high-resolution MS. An analytical method coupled with solid phase extraction was developed for acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, and thiamethoxam. Method detection limits were 0.47 to 2.1 ng L(-1) for six neonicotinoids. Dinotefuran was the most frequent and highest among the neonicotinoids examined in the aquatic environment in Osaka, Japan. The maximum concentration of dinotefuran was 220 ng L(-1). Given the toxicity of neonicotinoids for aquatic creatures, the concentrations observed here were substantially low. The change in concentrations was temporally coincident with the period of the neonicotinoid application. Although rapid photodegradation and some degradation products have been elucidated, the degradation products in the aquatic environment were not identified in the present study.

Use of thermally annealed multilayer gold nanoparticle films in combination analysis of localized surface plasmon resonance sensing and MALDI mass spectrometry.

A self-assembled film of gold nanoparticles (AuNPs) with a raspberry-like morphology was prepared on a glass plate by the layer-by-layer thermal annealing of multilayer films of AuNPs. It was possible to control the morphology of the obtained films of AuNPs by changing the annealing temperature, duration of annealing, and number of layers. On investigating the plasmonic properties of these films, we found that AuNP films with a raspberry-like morphology yielded the highest refractive index unit, which is a critical parameter in localized surface plasmon resonance (LSPR) sensing, as compared to other types of AuNP films. Self-assembled AuNP films with a raspberry-like morphology were subsequently functionalized with 11-mercaptoundecanoic acid (MUA) to enable the binding of lysozyme to the MUA-modified Au surface. The superior limit of detection for the LSPR sensing of lysozyme in a buffer solution was found to be in the picomolar range (∼10(-12) M). The high sensitivity observed in the region was attributed to the raspberry-like morphology, where the AuNPs were packed closely together, and the electromagnetic field confinement was most intense (i.e., at hot spots). The MUA-modified, self-assembled AuNP films with a raspberry-like morphology were finally used in the combination analysis of LSPR sensing and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for the selective detection and identification of lysozyme in human serum.

One-pot analysis of enantiomeric excess of free amino acids by electrospray ionization mass spectrometry.

An electrospray ionization mass spectrometric method for the simultaneous analysis of the enantiomeric excess of free amino acids, without chromatographic separation, was demonstrated using a quasi-racemic mixture of deuterium-labelled and unlabelled chiral copper(ii) complexes. This convenient method enables the simultaneous high-sensitivity determination of the enantiomeric excess of 12 amino acids.

Platinum nanoflowers on scratched silicon by galvanic displacement for an effective SALDI substrate.

We report a new and facile method for synthesizing 3D platinum nanoflowers (Pt Nfs) on a scratched silicon substrate by electroless galvanic displacement and discuss the applications of the Pt Nfs in surface-assisted laser desorption/ionization-mass spectrometry (SALDI-MS). Surface scratching of n-type silicon is essential to induce Pt Nf growth on a silicon substrate (to obtain a Pt Nf silicon hybrid plate) by the galvanic displacement reaction. The Pt Nf silicon hybrid plate showed excellent SALDI activity in terms of the efficient generation of protonated molecular ions in the absence of a citrate buffer. We propose that the acidity of the Si-OH moieties on silicon increases because of the electron-withdrawing nature of the Pt Nfs; hence, proton transfer from the Si-OH groups to the analyte molecules is enhanced, and finally, thermal desorption of the analyte ions from the surface occurs. Signal enhancement was observed for protonated molecular ions produced from a titania nanotube array (TNA) substrate on which Pt nanoparticles had been photochemically deposited. Moreover, surface modification of the Pt Nf silicon hybrid plate by perfluorodecyltrichlorosilane (FDTS) (to obtain an FDTS-Pt Nf silicon hybrid plate) was found to facilitate soft SALDI of labile compounds. More interestingly, the FDTS-Pt Nf silicon hybrid plate acts 1) as a high-affinity substrate for phosphopeptides and 2) as a SALDI substrate. The feasibility of using the FDTS-Pt Nf silicon hybrid plate for SALDI-MS has been demonstrated by using a ß-casein digest and various analytes, including small molecules, peptides, phosphopeptides, phospholipids, carbohydrates, and synthetic polymers. The hybridization of Pt Nfs with a scratched silicon substrate has been found to be important for achieving excellent SALDI activity.

Stability of the DMF-protected Au nanoclusters: photochemical, dispersion, and thermal properties.

We have reported the synthesis of dimethylformamide (DMF)-protected gold nanoclusters using a surfactant-free DMF reduction method. DMF-protected gold nanoclusters (Au NCs) are obtained without the formation of gold nanoparticles and bulk metals as byproducts using a hot injection process for the homogeneous reduction. The as-prepared DMF-protected Au NCs were a mixture of various-sized Au NCs with a cluster number of less than 20 including at least Au(8) and Au(13). The photoluminescence emission from Au(8) and Au(13) was confirmed in the photoluminescence spectra. The Au NCs are stabilized with DMF molecules through the interaction of amide groups of DMF with Au NCs. DMF-protected Au NCs in solution were found to have high thermal stability, high dispersion stability in various solvents, and high photochemical stability. The DMF-protected Au NCs dispersed well for at least a month in various solvents such as water, acid (pH 2), alkali (pH 12) and 0.5 M NaCl aqueous solution, and methanol without further surface modification. The thermal stability of DMF-protected Au NCs was approximately 150 degrees C, which was comparable to that of thiolate-protected Au NCs. The photobleaching of Au NCs in water gradually occurred under UV light irradiation (356 nm, 1.3 mW/cm(2)) because of the photoinduced oxidation of Au NCs. After 8 h irradiation, the fluorescence intensity slowly decreased to approximately 50% of the maximum and to approximately 20% after 96 h under the present condition, compared to the photobleaching of CdSe semiconductor quantum dots. We also found that the fluorescence intensity remained to be about 30% of the maximum even in the presence of concentrated 30% H(2)O(2). These findings demonstrate that the photobleaching process under the UV irradiation is effectively suppressed for DMF-protected Au NCs.

Semi-online nanoflow liquid chromatography/matrix-assisted laser desorption ionization mass spectrometry of synthetic polymers using an octadecylsilyl-modified monolithic silica capillary column.

We have designed a semi-online liquid chromatography/matrix-assisted laser desorption/ionization mass spectrometry (LC/MALDI-MS) system to introduce eluent from a octadecylsilyl (ODS) group modified monolithic silica capillary chromatographic column directly onto a sample plate for MALDI-MS analysis. Our novel semi-online system is useful for rapidly and sensitively examining the performance of a monolithic capillary column. An additional advantage is the small elution volume of a monolithic capillary column, which allows delicate eluents, such as 1,1,1,3,3,3,-hexafluoroisopropyl alcohol (HFIP), to be used to achieve cost-effective analysis. Using the semi-online LC/MALDI-MS system, chromatographic separation of polymers by the monolithic column with different eluents was studied. Separation of poly(methyl methacrylate) and Nylon 6/6 showed that the column functioned via size-exclusion separation when tetrahydrofuran or HFIP eluent was used. On the other hand, the separation behavior of Nylon 11 indicated a reversed-phase mode owing to the interaction of the polymer with the modified ODS group in the column. Using tetrahydrofuran/methanol (1:1, v/v) as the eluent, the LC/MALDI-MS spectra of poly(lactic acid), which contains both linear and cyclic polymer structures, showed that the column could separate the hydrophobic cyclic polymer and elute it out relatively slowly. The monolithic column functions basically via size-exclusion separation; the reversed-phase separation by interaction with the ODS functions may have less influence on column separation. The semi-online monolithic capillary LC/MALDI-MS method we have developed should provide a means of effectively analyzing synthetic polymers.

Enantioselectivity-Evaluation of Chiral Copper(II) Complexes Coordinated by Novel Chiral Tetradentate Ligands for Free Amino Acids by Mass Spectrometry Coupled With the Isotopically Labeled Enantiomer Method.

A series of copper(II) complexes with chiral tetradentate ligands, N,N'-ethylene- bis(S-amino acid methyl amide or methyl ester) prepared from S-alanine, S-phenylalanine, S-valine or S-proline, was generated in methanol. The copper complexes provided three component complexes in the presence of a free chiral amino acid. The enantioselectivity for the amino acid was evaluated by electrospray ionization-mass spectrometry coupled with the deuterium-labeled enantiomer method and these copper complexes were found to exhibit high enantioselectivity for free amino acids having bulky side chains. This result suggests that steric interaction between the tetradentate ligand and free amino acid was a major factor in chiral recognition. The copper complex with a chiral tetradentate ligand prepared from S-proline showed opposite enantioselectivity to copper complexes consisting of tetradentate ligands prepared from other S-amino acids. The conformational difference of the tetradentate ligand in the copper complex was found to be significant for enantioselectivity.