Exact Mass Measurements for α-Allenic Alcohol by Atmospheric Pressure Chemical Ionization/Time-of-flight Mass Spectrometry

Introduction　　α Allenicalcoholsareanimportantkindofusefulcompoundsinsyntheticchemistrybecauseoftheirunusualstructuresandhavebeenwidelyappliedtothesynthesisofthree orfive memberedoxygen containingcycliccom pounds.1 4 Thestructuresoffiveα allenicalcoholsareshowninFig .1.Theirmolecularstructuresbecomeunstablewhenion izedbyelectronimpact (EI) ,thusthedetectionoftheirmolecularionsM+ isalwaysnoteasy .SoitisdifficulttodeterminetheirexactmolecularmassbyEI (Fig .2 ) .Whentheyareionizedbychemica…     

Exact Mass Measurements for a-Allenic Alcohol by Atmospheric Pressure Chemical Ionization／Time-of-flight Mass Spectrometry

The atmospheric pressure chemical ionization/time,of-flight mass speetrmtry (APEI/TOF-MS) was applied to determine the mass of five a.aIIenic alcohols via their vrotonated molecu.lar ions nslna Imsifive ion mode. Polyethylene Idycol (PEG) was used as the hlternal reference. All results were obtained under the resolution of about 5000 FWHM (full width at the half maximum). Solvent effects were studied and the satired results were obtained in acetonitrile. Comvared with the theoreflcal values, nun absolute errors were less thRn 1.0 mmu. The efTeets Of nozzle pote.Jldal, push pulse potential, pug pulse potentlai, puO bias potential and ic(lulsltion rate on exact mass determina/lon were also discussed. APCI/TOF.MS is proven to be a very semi/ire analytical technique and an alternative ionizafion mode in analytical technique lablle compounds with relatively weak polarity, such as a-allenic alcohol.     

Can Nonpolar Polyisobutylenes be Measured by Electrospray Ionization Mass Spectrometry? Anion-Attachment Proved to be an Appropriate Method

Polyisobutylenes (PIBs) with different end-groups including chlorine, exo-olefin, hydroxyl, and methyl prepared from aliphatic and aromatic initiators were studied by electrospray ionization mass spectrometry (ESI-MS). Independently of the end-groups, presence or absence of aromatic initiator moiety, these PIB derivatives were capable of forming adduct ions with NO₃ ^– and Cl^– ions, thus allowing the direct characterization of these compounds in the negative ion mode of ESI-MS. To obtain [PIB + NO₃]^– and [PIB + Cl]^– adduct ions with appreciable intensities, addition of polar solvents such as acetone, 2-propanol, or ethanol to the dichloromethane solution of PIBs was necessary. Furthermore, increasing both the polarity (by increasing the acetone content) and the ion-source temperature give rise to enhanced intensities for both [PIB + NO₃]^– and [PIB + Cl]^– ions. Energy-dependent collision induced dissociation studies (CID) revealed that increasing the collision voltages resulted in the shift of the apparent molecular masses to higher ones. CID studies also showed that dissociation of the [PIB + Cl]^– ions requires higher collision energy than that of [PIB + NO₃]^–. In addition, Density Functional Theory calculations were performed to gain insights into the nature of the interactions between the highly non-polar PIB chains and anions NO₃ ^– and Cl^– as well as to determine the zero-point corrected electronic energies for the formation of [PIB + NO₃]^– and [PIB + Cl]^– adduct ions.

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Determination of Fatty Acids in Three Nitraria Species by Precolumn Fluorescence Labeling for High-Performance Liquid Chromatography and Atmospheric Pressure Chemical Ionization–Mass Spectrometry

A novel fluorescence method using 2-(7-methyl-1H-pyrazolo-[3,4-b] quinoline-1-yl) ethyl-4-methyl benzenesulfonate as the labeling reagent was established for high-performance liquid chromatography determination of fatty acids. The conditions were optimized, including the identity of the organic solvent, identity, and amount of catalyst, amount of derivatization reagent, derivatization temperature, and derivatization time. The results indicated that quantitative yields of derivative were obtained with a five-fold molar excess of reagent at 90°C for 30 min using 25 mg of potassium carbonate as the catalyst. Atmospheric pressure chemical ionization mass spectrometry results indicated that collision-induced dissociation of protonated fatty acid derivatives produced fragments at m/z 228.2, m/z 210.2, and m/z 183.8. The method was validated in terms of linearity, limits of detection, limits of quantification, precision, and accuracy, and the results showed that the method exhibited excellent sensitivity, selectivity, and reproducibility. Limits of detection and limits of quantification were in the ranges of 0.52–2.34 ng mL^?1 and 1.23–6.63 ng mL^?1, respectively. This method was successfully applied to the determination of fatty acids in sarcocarps, seeds, and leaves of Nitraria tangutorum Bobr., Nitraria sibirica Pall., and Nitraria roborowskii Kom. The results indicated that the main components were oleic, linoleic, linolenic, and hexadecanoic acids. However, the composition of fatty acids in the tissues varied considerably.     

Analysis of the Products from the Oxidation of Geting Bituminous Coal by Atmospheric Pressure Photoionization–Mass Spectrometry

Geting bituminous coal was directly oxidized in aqueous sodium hypochlorite. The reaction mixture was sequentially extracted with ethyl ether and ethyl acetate. Both extracts were esterified with diazomethane to obtain methyl esterified products, which were analyzed using high performance liquid chromatography–mass spectrometry with electrospray ionization or atmospheric pressure photoionization. A large number of low- and nonpolar products with relatively high molecular masses were determined using atmospheric pressure photoionization mass spectrometry. Toluene and a toluene/anisole mixture (vol/vol = 95:5) were added to the atmospheric pressure photoionization system as dopants. Toluene induced better ionization than the toluene/anisole mixture in both ion signal intensity and number of detected species. Most of the molecular associated compounds contained heteroatoms.     

Monitoring the Hydrolysis of p—Nitrophenyl Acetate Catalyzed by Seryl—histidine with Electrospray Ionization Mass Spectrometry

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Comparative Study of Electrospray and Atmospheric Pressure Chemical Ionization with Liquid Chromatography–Mass Spectrometry for Quantification of Five Antihyperglycemic Agents Utilizing Monolithic Column

Liquid chromatography-mass spectrometry (LC-MS) in atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) modes were studied for a multi-component plasma and urine quantification of 5 antihyperglycemic agents (metformin, pioglitazone, gliclazide, glibenclamide, and glimperide). The separation of the compounds was achieved using Chromolith Performance RP-18e column (100 × 4.6 mm), with gradient mobile phase composition of acetonitrile ?0.1% formic acid. MS parameters for APCI and ESI were optimized individually and were operated in positive mode. The detection limits for the metformin, pioglitazone, glibenclamide, and glimepiride were determined to be 6.84, 6.22, 13.03, and 44.38 ng mL^?1 using LC-ESI-MS; and for LC-APCI-MS, it was determined to be 48.39, 8.02, 17.02, and 144.55 ng mL^?1, respectively. Gliclazide was the only exception as it exhibited a lower limit of detection (LOD) using APCI than ESI which was found to be 5.61 and 23.43 ng mL^?1, respectively. The method was validated for system suitability, linearity, precision and accuracy, specificity, stability, and robustness. The ESI as compared to APCI was found superior in many analytical parameters. The assay has been applied successfully to biological fluids (plasma and urine) of healthy volunteers.     

Determination of Ferulic Acid in Rat Plasma by Liquid Chromatography–Tandem Mass Spectrometry Method: Application to a Pharmacokinetic Study

Abstract

A rapid, sensitive, and specific liquid chromatography–tandem mass spectrometric (HPLC-MS/MS) method has been developed for quantification of ferulic acid in rat plasma. The analyte and docetaxel (internal standard) were extracted from plasma samples with diethyl ether and analyzed on a C₁₈ column. The chromatographic separation was achieved within 3.5 min by using acetonitrile-water as the mobile phase and the flow rate was 0.2 mL · min^?1. The method was linear within the range of 0.5 ? 800 ng · mL^?1. The lower limit of quantification (LLOQ) was 0.5 ng · mL^?1. Finally, the method is successfully applied for the pharmacokinetic study of ferulic acid in rats following intravenous administration.     

Detection of Radical Adducts with Small Molecular Weights by Matrix-Assisted Laser Desorption/Ionization with Fourier Transform Mass Spectrometry

As an alternative method, matrix-assisted laser desorption/ionization with Fourier transform mass spectrometry （MALDI-FTMS） has been successfully used to detect and identify free radical adducts with small molecular weights of hydroxyl and 2-cyano-2-propyl radicals trapped with 5,5-dimethylpyrroline N-oxide （DMPO）. The detection and identification by MS/MS experiments using sustained offresonance irradiation collision-induced dissociation （SORI-CID） of [（DMPO＋·OH-·H）＋H^＋] （m/z 130.0868） and [DMPO＋2 ·CH（CH3）2CN＋H^＋] （m/z 250.1917） have demonstrated that MALDI-FTMS could be an effective method for detection and identification of free radical adducts. Other radical adducts have been also detected and identified. The approach of MALDI-FTMS is simple, fast, and sensitive which has potential for high-throughput analysis.     

Determination of Macrolide Antibiotics Using Dispersive Liquid–Liquid Microextraction Followed by Surface-Assisted Laser Desorption/Ionization Mass Spectrometry

A novel method for the determination of macrolide antibiotics using dispersive liquid–liquid microextraction coupled to surface-assisted laser desorption/ionization mass spectrometric detection was developed. Acetone and dichloromethane were used as the disperser solvent and extraction solvent, respectively. A mixture of extraction solvent and disperser solvent were rapidly injected into a 1.0 mL aqueous sample to form a cloudy solution. After the extraction, macrolide antibiotics were detected using surface-assisted laser desorption/ionization mass spectrometry (SALDI/MS) with colloidal silver as the matrix. Under optimum conditions, the limits of detection (LODs) at a signal-to-noise ratio of 3 were 2, 3, 3, and 2 nM for erythromycin (ERY), spiramycin (SPI), tilmicosin (TILM), and tylosin (TYL), respectively. This developed method was successfully applied to the determination of macrolide antibiotics in human urine samples.     

Specific Cα-C Bond Cleavage of β-Carbon-Centered Radical Peptides Produced by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

Radical-driven dissociation (RDD) of hydrogen-deficient peptide ions [M???H?+?H]^·+ has been examined using matrix-assisted laser dissociation/ionization in-source decay mass spectrometry (MALDI-ISD MS) with the hydrogen-abstracting matrices 4-nitro-1-naphthol (4,1-NNL) and 5-nitrosalicylic acid (5-NSA). The preferential fragment ions observed in the ISD spectra include N-terminal [a]?+?ions and C-terminal [x]⁺, [y?+?2]⁺, and [w]⁺ ions which imply that β-carbon (Cβ)-centered radical peptide ions [M???Hβ?+?H]^·+ are predominantly produced in MALDI conditions. RDD reactions from the peptide ions [M???Hβ?+?H]^·+ successfully explains the fact that both [a]⁺ and [x]⁺ ions arising from cleavage at the Cα-C bond of the backbone of Gly-Xxx residues are missing from the ISD spectra. Furthermore, the formation of [a]⁺ ions originating from the cleavage of Cα-C bond of deuterated Ala(d3)-Xxx residues indicates that the [a]⁺ ions are produced from the peptide ions [M???Hβ?+?H]^·+ generated by deuteron-abstraction from Ala(d3) residues. It is suggested that from the standpoint of hydrogen abstraction via direct interactions between the nitro group of matrix and hydrogen of peptides, the generation of the peptide radical ions [M???Hβ?+?H]^·+ is more favorable than that of the α-carbon (Cα)-centered radical ions [M???Hα?+?H]^·+ and the amide nitrogen-centered radical ions [M???H_N?+?H]^·+, while ab initio calculations indicate that the formation of [M???Hα?+?H]^·+ is energetically most favorable.

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The FUNPET—a New Hybrid Ion Funnel-Ion Carpet Atmospheric Pressure Interface for the Simultaneous Transmission of a Broad Mass Range

An atmospheric pressure interface transports ions from ambient pressure to the low-pressure environment of a mass spectrometer. A capillary coupled to an ion funnel is widely used. However, conventional ion funnels do little to negate the large amount of energy picked up by high-mass ions from the gas flow through the capillary. There has been little work done on the effects of gas flow on ion transmission, and the previous studies have all been limited to low-mass, low-charge ions. In this work, we account for the effects of gas flow, diffusion, and electric fields (static and oscillating) on ion trajectories and use simulations to design a new hybrid ion funnel-ion carpet (FUNPET) interface that transmits a broad mass range with a single set of instrument conditions. The design incorporates a virtual jet disruptor where pressure buildup and counter flow dissipate the supersonic jet that results from gas flow into the interface. This, and the small exit aperture that can be used with the FUNPET, reduces the gas flow into the next stage of differential pumping. The virtual jet disruptor thermalizes ions with a broad range of masses (1 kDa to 1 GDa), and once thermalized, they are transmitted into next region of the mass spectrometer with low excess kinetic energy. The FUNPET interface is easy to fabricate from flexible printed circuit board and a support frame made by 3D printing. The performance of the interface was evaluated using charge detection mass spectrometry.

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Rapid Determination of Adenine Arabinoside Monophosphate in Pharmaceutical Injections by Droplet Spray Ionization – Tandem Mass Spectrometry (DSI-MS/MS)

Abstract

Rapid analysis of pharmaceutical preparations is of great interest in clinical studies with benefits for identifying counterfeit drugs. In this study, droplet spray ionization tandem mass spectrometry (DSI-MS/MS) was developed for the rapid determination of adenine arabinoside monophosphate in pharmaceutical injections without complex sample pretreatment. The sample solution was loaded on the slip corner placed in front of the inlet of a mass spectrometer, and high voltage was applied to the solution to create a charged spray from the corner for MS analysis. The sample was loaded for analysis without additional sample preparation protocols, which greatly simplifies the operation. The limit of detection and limit of quantification were determined to be 2.7 and 9.1?ng/mL, respectively. The recoveries were in the range from 96% to 112%, and the calculated relative standard deviations were less than 7% for the DSI-MS/MS method. Three adenine arabinoside monophosphate pharmaceutical injection samples and a degraded sample obtained by acid treatment at 40?°C were successfully analyzed by directly dissolving and diluting the sample. Moreover, the sample-loading step required only 2?s. Together these capabilities indicate that the DSI-MS/MS is a simple and robust method and has promising applications in pharmacology studies without complicated sample pretreatment.     

Liquid Chromatography–Electrospray Ionization–Mass Spectrometric Method for the Determination of Hydrochlorothiazide in Human Plasma: Application to a Pharmacokinetic Study

Abstract

A rapid, convenient, and sensitive liquid chromatography–electrospray ionization–mass spectrometry method was developed and validated for the quantification of hydrochlorothiazide in human plasma. The samples were first spiked with the internal standard, and the analyte was then extracted with ethyl acetate. The chromatographic separation was achieved on a C₁₈ column by using water–acetonitrile (68:32, v/v) as mobile phase. The method was linear within the range of 2.5–200 ng/ml. The lower limit of quantification was 1.0 ng/ml. Finally, the validated method was successfully applied for the evaluation of the pharmacokinetic profiles of hydrochlorothiazide in healthy male Chinese volunteers.     

Microwave Assisted Extraction of Polycyclic Aromatic Hydrocarbons and their Determination by Gas Chromatography–Mass Spectrometry: Validation of the Method and Application to Marine Sediments

Microwave-assisted extraction of sixteen polycyclic aromatic hydrocarbons and their gas chromatographic mass spectrometric detection are presented herein. An efficient extraction was achieved in 15 minutes using 10 mL of 1:1 n-hexane-acetone while a clean-up step was developed studying the elution curves on solid phase extraction silica cartridges. The analytical method was optimized and validated using a certified reference marine sediment; satisfactory figures of merit were obtained with limits of detection in the range 0.001–0.004 µg/g, precision within 6%, and good linearity (regression coefficients generally higher than 0.998, in the concentration range 0.010–1.000 µg/mL). The developed method was successfully applied to the determination of polycyclic aromatic hydrocarbons in real marine sediments collected in two coastal areas of Italy exposed to different anthropic impact: three tourist sites of Liguria and the Venetian Lagoon. The total concentration of the analytes in the samples was in the range 1.027–3.827 µg/g and the use of common markers suggested their probable pyrolytic origin.     

Reply to the Correspondence on “Crystalline Porous Organic Salt for Ultrarapid Adsorption/Desorption-Based Atmospheric Water Harvesting by Dual Hydrogen Bond System”

White et al., in a recent Correspondence, provided additional structural data to illustrate that CPOS-6 undergoes a single-crystal-to-single-crystal transformation during water adsorption/desorption. This finding gave a better understanding of the relevant experimental phenomena from the perspective of structural transformation and is a good complement to our previous results. However, we wish to emphasize that our research focuses on the kinetic behavior of water during ultrafast adsorption/desorption in nano-confined channels. Herein, we further interpret the rapid transport of water molecules in the nano-confined channels from the perspective of superfluidity.     

Analysis of Codeine in Urine and Opiate Sample by Solid-Phase Microextraction (SPME) and Gas Chromatography——Mass Spectrometry (GC/MS)

The growth of the illegal heroin use has stimulated widespread testing for its abuse. However, since the heroin metabolizes quickly in the human body and not reliably detected in urine,its metabolites are by necessity the analytical targets for the detection of its intake. Of the metabolites of street heroin,codeine is important one. Thus,the analysis of codeine in urine also become an important application for the detection of street heroin intake. There are extensive literature on the determination of codeine in biological samples using gas chromatography/mass spectrometry(GC/MS). In those methods,the analytes were isolated by liquid-liquid or solid-phase extraction from the urine. Such procedure suffers from the requirement of high purity solvent and time consuming.     

Study of a Ru-La/ZrO_2 Catalyst Prepared by Precipitation Method for Selective Hydrogenation of Benzene to Cyclohexene

1. Introduction Cyclohexene as an important intermediate prod- uct is widely used in chemical productions. The process of selective hydrogenation of benzene to cyclo- hexene has been an important research topic in green chemistry owing to its atomic economy and clean production [1]. In order to attain greater economic benefits, researchers are searching for a new catalytic system that is high in activity and selectivity, simple in technology, and low in cost. In this respect, some progresses h…