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.

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.

Mass spectrometric detection of enantioselectivity in three-component complexation, copper(ii)-chiral tetradentate ligand-free amino acid in solution.

By using electrospray ionization mass spectrometry coupled with the use of deuterium-labelled quasienantiomers, enantioselective coordination of a free amino acid as the second ligand of a copper(ii) complex with a novel chiral tetradentate ligand was evaluated quantitatively in a short measurement time.

Enhanced degradation of chitosan by applying plasma treatment in combination with oxidizing agents for potential use as an anticancer agent.

Solution plasma (SP) treatment in combination with oxidizing agents, i.e., hydrogen peroxide (H2O2), potassium persulfate (K2S2O8) and sodium nitrite (NaNO2) were adopted to chitosan degradation in order to achieve fast degradation rate, low chemicals used and high yield of low-molecular-weight chitosan and chitooligosaccharide (COS). Among the studied oxidizing agents, H2O2 was found to be the best choice in terms of appreciable molecular weight reduction without major change in chemical structure of the degraded products of chitosan. By the combination with SP treatment, dilute solution of H2O2 (4-60mM) was required for effective degradation of chitosan. The combination of SP treatment and dilute solution of H2O2 (60mM) resulted in the great reduction of molecular weight of chitosan and water-soluble chitosan was obtained as a major product. The resulting water-soluble chitosan was precipitated to obtain COS. An inhibitory effect against cervical cancer cell line (HeLa cells) of COS was also examined.

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.

Identification of Anthropogenic Compounds in Urban Environments and Evaluation of Automated Methods for Reading Fragmentation-A Case of River Water.

A workflow based on liquid chromatography/high-resolution mass spectrometry (LC/HR-MS) was applied for the identification of compounds in urban environments. Substances extracted by solid-phase extraction from river water were wholly analyzed by LC/HR-MS without any purification. Fragmentation in collision-induced dissociation was manually studied for the 20 most intense ions in positive- and negative-ion electrospray ionization with accurate mass determination at a resolution of 100,000. Sixteen anthropogenic compounds in the extract were identified and confirmed using standard reference reagents. These compounds consisted of pharmaceuticals, surfactants, flame retardants, and industrial intermediates. The majority of the compounds are common in our daily life. In the identification process, two automated methods, MAGMa and MetFrag/MetFusion, for reading fragmentation were evaluated for the sixteen compounds. Although automated methods could be used to retrieve the correct molecular structures in most cases, they could not always be promoted to the top rank. Automated methods have yet to be a complete solution for identifying chemical compounds, but will considerably reduce the burden for humans in reading fragmentation.

Direct Imaging Mass Spectrometry of Plant Leaves Using Surface-assisted Laser Desorption/Ionization with Sputter-deposited Platinum Film.

Plant leaves administered with systemic insecticides as agricultural chemicals were analyzed using imaging mass spectrometry (IMS). Matrix-assisted laser desorption/ionization (MALDI) is inadequate for the detection of insecticides on leaves because of the charge-up effect that occurs on the non-conductive surface of the leaves. In this study, surface-assisted laser desorption/ionization with a sputter-deposited platinum film (Pt-SALDI) was used for direct analysis of chemicals in plant leaves. Sputter-deposited platinum (Pt) films were prepared on leaves administered with the insecticides. A sputter-deposited Pt film with porous structure was used as the matrix for Pt-SALDI. Acephate and acetamiprid contained in the insecticides on the leaves could be detected using Pt-SALDI-MS, but these chemical components could not be adequately detected using MALDI-MS because of the charge-up effect. Enhancement of ion yields for the insecticides was achieved using Pt-SALDI, accompanied by prevention of the charge-up effect by the conductive Pt film. The movement of systemic insecticides in plants could be observed clearly using Pt-SALDI-IMS. The distribution and movement of components of systemic insecticides on leaves could be analyzed directly using Pt-SALDI-IMS. Additionally, changes in the properties of the chemicals with time, as an indicator of the permeability of the insecticides, could be evaluated.

Reduced Sampling Size with Nanopipette for Tapping-Mode Scanning Probe Electrospray Ionization Mass Spectrometry Imaging.

Mass spectrometry imaging (MSI) with ambient sampling and ionization can rapidly and easily capture the distribution of chemical components in a solid sample. Because the spatial resolution of MSI is limited by the size of the sampling area, reducing sampling size is an important goal for high resolution MSI. Here, we report the first use of a nanopipette for sampling and ionization by tapping-mode scanning probe electrospray ionization (t-SPESI). The spot size of the sampling area of a dye molecular film on a glass substrate was decreased to 6 µm on average by using a nanopipette. On the other hand, ionization efficiency increased with decreasing solvent flow rate. Our results indicate the compatibility between a reduced sampling area and the ionization efficiency using a nanopipette. MSI of micropatterns of ink on a glass and a polymer substrate were also demonstrated.

Simultaneous detection of phosphatidylcholines and glycerolipids using matrix-enhanced surface-assisted laser desorption/ionization-mass spectrometry with sputter-deposited platinum film.

Matrix-assisted laser desorption/ionisation (MALDI) imaging mass spectrometry (IMS) allows for the simultaneous detection and imaging of several molecules in brain tissue. However, the detection of glycerolipids such as diacylglycerol (DAG) and triacylglycerol (TAG) in brain tissues is hindered in MALDI-IMS because of the ion suppression effect from excessive ion yields of phosphatidylcholine (PC). In this study, we describe an approach that employs a homogeneously deposited metal nanoparticle layer (or film) for the detection of glycerolipids in rat brain tissue sections using IMS. Surface-assisted laser desorption/ionisation IMS with sputter-deposited Pt film (Pt-SALDI-IMS) for lipid analysis was performed as a solvent-free and organic matrix-free method. Pt-SALDI produced a homogenous layer of nanoparticles over the surface of the rat brain tissue section. Highly selective detection of lipids was possible by MALDI-IMS and Pt-SALDI-IMS; MALDI-IMS detected the dominant ion peak of PC in the tissue section, and there were no ion peaks representing glycerolipids such as DAG and TAG. In contrast, Pt-SALDI-IMS allowed the detection of these glycerolipids, but not PC. Therefore, using a hybrid method combining MALDI and Pt-SALDI (i.e., matrix-enhanced [ME]-Pt-SALDI-IMS), we achieved the simultaneous detection of PC, PE and DAG in rat brain tissue sections, and the sensitivity for the detection of these molecules was better than that of MALDI-IMS or Pt-SALDI alone. The present simple ME-Pt-SALDI approach for the simultaneous detection of PC and DAG using two matrices (sputter-deposited Pt film and DHB matrix) would be useful in imaging analyses of biological tissue sections.

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks.

A simple, high-concentration (up to 0.6 M Cu salt) synthesis of sub-10-nm copper nanoparticles (Cu NPs) was developed in ethylene glycol at room temperature under ambient air conditions using 1-amino-2-propanol (AmIP) as the stabilizer. Monodispersed AmIP-Cu NPs of 3.5 ± 1.0 nm were synthesized in a high yield of ∼90%. Thus, nearly 1 g of sub-10-nm Cu NP powder was obtained using a one-step synthesis for the first time. It is proposed that metallacyclic coordination stability of a five-membered ring type between the Cu and AmIP causes the high binding force of Am IP onto the Cu surface, resulting in the superior stability of the AmIP-Cu NPs in a solution. The purified powder of AmIP-Cu NPs can be redispersed in alcohol-based solvents up to high Cu contents of 45 wt % for the preparation of Cu nanoink. The resistivity of the conductive Cu film obtained from the Cu nanoink was 30 µΩ cm after thermal heating at 150 °C for 15 min under a nitrogen flow. The long-term resistance stability of the Cu film under an air atmosphere was also demonstrated.

Hydrazide and hydrazine reagents as reactive matrices for matrix-assisted laser desorption/ionization mass spectrometry to detect steroids with carbonyl groups.

Fifty-one reagents (37 hydrazides and 14 hydrazines) were examined to determine if they could function as reactive matrices for the detection of steroids with carbonyl groups in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Among these reagents, 3-hydroxy-2-naphthoic acid hydrazide reacted most efficiently with steroids with carbonyl groups, allowing detection of them at the 1pmol level. Results from accurate mass measurement with a JMS-S3000 Spiral-TOF suggested that the ion peaks corresponding to the protonated fragment of a hydrazone were observed, in addition to the protonated molecular peaks of the resulting hydrazones ([M(D)+H](+)) and their sodium adduct ([M(D)+Na](+)). 3-Hydroxy-2-naphthoic acid hydrazide also could detect cortisol (1.93ng) spiked in a human serum certified reference material, as well as cortisone and cortisol in a human saliva sample collected in the morning. Using a combination of 3-hydroxy-2-naphthoic acid hydrazide and α- cyano-4-hydroxycinammic acid (CHCA) (3-hydroxy-2-naphthoic acid hydrazide:CHCA=4:1, v/v), even cortisone and cortisol in a human saliva sample collected in the afternoon, when levels are typically low, could be detected effectively.

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.

Laser Desorption/Ionization Mass Spectrometry (LDI-MS) of Lipids with Iron Oxide Nanoparticle-Coated Targets.

Iron oxide nanoparticle (NP)-coated target plates were employed for the direct detection and analysis of low molecular weight lipids by laser desorption/ionization (LDI) mass spectrometry (MS). We have demonstrated that the use of the iron oxide NP-coated target provides a simple, direct, and rapid detection method for lipid standards and epidermal surface lipids without any cumbersome sample pretreatment as well as mass spectra that are free of background matrix peaks. Lipid standards (1-stearoyl-sn-glycero-3-phosphocholine, 1,2-dioleoyl-sn-glycerol, 1-palmitoyl-2-oleoyl-3-linoleoyl-rac-glycerol, 1,2-distearoyl-sn-glycero-3-phosphocholine) were detected as either protonated or cationated species. Clean MS/MS spectra for each lipid were also successfully obtained. Pre-MS surface cleaning of the target plates with UV-ozone treatment successfully removed organic contaminants that would interfere with the mass spectra especially in the low molecular weight region. Preliminary application of the presented target plate to the detection of endogenous lipids in latent fingerprints showed promising results and for potential use in the visualization and chemical composition determination of latent fingerprints by nanoparticle assistance.

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.

A physical operation of hydrodynamic orientation of an azobenzene supramolecular assembly with light and sound.

Photoisomerizations of a newly designed azobenzene derivative reversibly change its self-assembly in a solution to form twisted supramolecular nanofibers and amorphous aggregates, respectively. When irradiating the sample solution with audible sound, the former assembly exhibits a LD response due to its hydrodynamic orientation, but the latter one is LD silent, in the sound-induced fluid flows.

Gold-decorated titania nanotube arrays as dual-functional platform for surface-enhanced Raman spectroscopy and surface-assisted laser desorption/ionization mass spectrometry.

In this report, we demonstrate gold-decorated titania nanotube arrays (Au-TNA substrate) as a dual-functional platform for surface-enhanced Raman spectroscopy (SERS) and surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The Au nanoparticles are grown on the substrate using vapor deposition of Au. The resulting substrates perform better than Au colloids in terms of the reproducibility of the SERS measurements, long-term stability of the fabricated structures, and clean surface of the Au. The nanostructure of the Au-TNA substrate was designed to optimize the SALDI-MS and SERS performance. Excellent reproducibility of the SERS measurements using the Au-TNA substrate was obtained, with a standard error less than 6 %. SALDI activity was also demonstrated for the same Au-TNA substrates. Finally, the Au-TNA substrate was used for combined SERS and SALDI-MS analysis (i) to discriminate the structural isomers of pyridine compounds (para-, meta-, and ortho-pyridinecarboxylic acid) and (ii) to detect polycarbamate, a dithiocarbamate fungicide. These results are difficult to obtain using either approach alone.

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.

Sensitive Detection of Aromatic Hydrophobic Compounds in Water and Perfluorooctane Sulfonate in Human Serum by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS) with Amine Functionalized Graphene-Coated Cobalt Nanoparticles.

In this article, we describe the application of surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) with the use of amine functionalized graphene-coated cobalt nanoparticles (CoC-NH2 nanoparticles) to analyse aromatic hydrophobic compounds that are known environmental contaminants, including polycyclic aromatic hydrocarbons (PAHs) and pentachlorophenol (PCP). Our results demonstrated that SALDI-MS can detect PCP, anthracene, and pyrene in water. In particular, the CoC-NH2 nanoparticles proved to be an efficient means of capturing PCP in water because of the high adsorption capacity of the nanoparticles for PCP, which resulted in a detectability of 100 ppt. Furthermore, the CoC-NH2 nanoparticles also functioned as an adsorbent for solid-phase extraction of perfluorooctane sulfonate (PFOS) from human serum, displaying good performance with a detectability of 10 ppb by SALDI-MS.