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Analytical Chemistry

Chemistry Faculty Publications

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Full-Text Articles in Chemistry

Secondary N-Nitrosocarbamate Anions: Structure And Alkylation Reactions. A Dft Study, Vladimir Benin May 2006

Secondary N-Nitrosocarbamate Anions: Structure And Alkylation Reactions. A Dft Study, Vladimir Benin

Chemistry Faculty Publications

The current article reports theoretical studies (DFT: B3LYP/6-31+G(d)) on the structure and alkylation reactions of the anions of some secondary N-nitrosocarbamates, a class of ambident nucleophiles whose chemistry has been little explored. Several anions (1–4), with an increasing size of the carbamate alkyl (aryl) group were investigated, in an attempt to establish the influence of the size of that group on the thermal stability and regioselectivity of alkylation of the title anions. The conclusion is that thermal stability and the mode of reaction are affected significantly only in the presence of very large and branched carbamate groups. The thermal …

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Preparation Of Some Substituted Terephthalic Acids, Susanna Branion, Vladimir Benin Jan 2006

Preparation Of Some Substituted Terephthalic Acids, Susanna Branion, Vladimir Benin

Chemistry Faculty Publications

We report in detail the preparation of two substituted terephthalic acids: 2‐sulfomethylterephthalic acid (1) and 2‐phosphonoterephthalic acid (2). Efficient, short syntheses have been developed for both compounds. They are potentially useful monomers for construction of acid‐pendant polymer chains.

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Preparation, Characterization And Dft Studies Of Some New N-Nitrosocarbamates And N-Nitrosoureas, Ragavan Narayanan, Helene Hedian, Eric Shamo, Vladimir Benin Jan 2006

Preparation, Characterization And Dft Studies Of Some New N-Nitrosocarbamates And N-Nitrosoureas, Ragavan Narayanan, Helene Hedian, Eric Shamo, Vladimir Benin

Chemistry Faculty Publications

We are presenting the preparation, characterization and density functional theory (DFT) studies {B3LYP/6-31+G(d)) of several reiated classes of N-nitrosocarbamates and N-nitrosoureas. The iong-range goal is the design and preparation of compounds, which would undergo photochemical or hydrolytic decomposition, to yield stabilized cyclic cations that can serve as alkylating agents at various nucleophilic centers, including DNA bases.

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Synthesis, Structural Studies And Desilylation Reactions Of Some N-2-(Trimethylsilyl)Ethyl-N-Nitrosocarbamates, Arpitha Thakkalapally, Vladimir Benin May 2005

Synthesis, Structural Studies And Desilylation Reactions Of Some N-2-(Trimethylsilyl)Ethyl-N-Nitrosocarbamates, Arpitha Thakkalapally, Vladimir Benin

Chemistry Faculty Publications

The present report describes the preparation and characterization of several N-2-(trimethylsilyl)ethyl-N-nitrosocarbamates, designed as precursors to thermally unstable secondary N-nitrosocarbamate anions via fluoride-assisted cleavage. X-ray structural studies demonstrate that the core N-nitrosocarbamate moiety has a nearly planar geometry, with an s-E orientation at the N–N bond. DFT calculations (B3LYP/6-31+G(d)) reproduce accurately the structural features of the title compounds and detailed conformational analysis at the same level of theory addresses the long-standing issue of preferred geometries for three classes of related structures: N-nitrosocarbamates, N-nitrosoureas and N-nitrosoamides. Desilylation studies demonstrate that both the …

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Measurement Of The Anticancer Agent Gemcitabine And Its Deaminated Metabolite At Low Concentrations In Human Plasma By Liquid Chromatography-Mass Spectrometry, Yan Xu, Bruce Keith, Jean L. Grem Apr 2004

Measurement Of The Anticancer Agent Gemcitabine And Its Deaminated Metabolite At Low Concentrations In Human Plasma By Liquid Chromatography-Mass Spectrometry, Yan Xu, Bruce Keith, Jean L. Grem

Chemistry Faculty Publications

A liquid chromatography/mass spectrometry (LC-MS) method has been developed and validated for the determination of the anticancer agent gemcitabine (dFdC) and its metabolite 2′,2′-difluoro-2′-deoxyuridine (dFdU) in human plasma. An Oasis® HLB solid phase extraction cartridge was used for plasma sample preparation. Separation of the analytes was achieved with a YMC ODS-AQ (5 μm, 120 Å, mm) column. The initial composition of the mobile phase was 2% methanol/98% 5 mM ammonium acetate at pH 6.8 (v/v), and the flow rate was 0.2 ml/min. An isocratic gradient was used for 3 min, followed by a linear gradient over 4 min to 30% …

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Measurement Of Anti-Cancer Agent Methoxyamine In Plasma By Tandem Mass Spectrometry With On-Line Sample Extraction, Shuming Yang, Lili Liu, Stanton L. Gerson, Yan Xu Oct 2003

Measurement Of Anti-Cancer Agent Methoxyamine In Plasma By Tandem Mass Spectrometry With On-Line Sample Extraction, Shuming Yang, Lili Liu, Stanton L. Gerson, Yan Xu

Chemistry Faculty Publications

In this work, we present the development and validation of a tandem mass spectrometry method for the quantitative determination of methoxyamine (CH3ONH2), a potential new chemotherapeutic agent, in human and mouse plasma. Methoxyamine together with the internal standard (I.S.) methoxyl-D3-amine was directly derivatized in plasma sample with a novel chemical agent 4-(N,N-diethylamino)benzaldehyde. The product solution was injected into an on-line Oasis® HLB extraction column ( mm) for analyte extraction. After the elution of extractives, the derivatized analytes were monitored by the positive-electrospray-ionization mass spectrometry (ESI-MS-MS). The structures of derivatized analytes were elucidated by fragmentation. Quantitation of plasma methoxyamine was carried …

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Measurement Of The Anti-Cancer Agent Gemcitabine In Human Plasma By High-Performance Liquid Chromatography, Bruce Keith, Yan Xu, Jean L. Grem Feb 2003

Measurement Of The Anti-Cancer Agent Gemcitabine In Human Plasma By High-Performance Liquid Chromatography, Bruce Keith, Yan Xu, Jean L. Grem

Chemistry Faculty Publications

A reversed-phase HPLC assay has been developed to determine the concentration of the anti-metabolite 2′,2′-difluorodeoxycytidine (gemcitabine, dFdC) in human plasma over the concentration range of 0.5–150 μM (0.13–39.44 μg/ml), and 2′,2′-difluorodeoxyuridine (dFdU), the deaminated, inactive metabolite, over the range of 1.0–227 μM (0.26–60 μg/ml). After the addition of 20 nmol 2′-fluorodeoxycytidine (FdC) as an internal standard, 0.5-ml samples of plasma were subjected to acetonitrile precipitation, followed by analysis using a gradient reversed-phase HPLC assay with UV detection. A Phenomenex Columbus™ C18 column, 5 μm, 150×4.6 mm, and a Waters C18, 4 μm, Nova-Pak Sentry guard column were used to achieve …

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Liquid Chromatography–Mass Spectrometry Method For The Analysis Of The Anti-Cancer Agent Capecitabine And Its Nucleoside Metabolites In Human Plasma, Yan Xu, Jean L. Grem Jan 2003

Liquid Chromatography–Mass Spectrometry Method For The Analysis Of The Anti-Cancer Agent Capecitabine And Its Nucleoside Metabolites In Human Plasma, Yan Xu, Jean L. Grem

Chemistry Faculty Publications

A reversed-phase high-performance liquid chromatography method with electrospray ionization and mass spectral detection is described for the determination of capecitabine, 5′-deoxy-5-fluorocytidine and 5′-deoxy-5-fluorouridine in human plasma with 5-chloro-2′-deoxyuridine as the internal standard. An on-line sample clean-up procedure allows dilution of the plasma sample with the initial mobile phase. The linear dynamic range is 0.0500–10.0 μg/ml for capecitabine, and 0.0500–25.0 μg/ml for the metabolites, 5′-deoxy-5-fluorocytidine and 5′-deoxy-5-fluorouridine, respectively. This method has been used to analyze plasma samples from patients receiving capecitabine in combination with oxaliplatin.

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Possible Cobalt-Cobalt Bridging By A Hemiacetal In The Dinuclear Cobalt Complex Bearing The Ligand Bis(3-(2-Pyridylmethyleneamino)Phenyl) Sulfone, Armando M. Guidote Jr, Tomoko Imajo, Yasuhiko Kurusu, Yoshiro Masuyama Jan 2003

Possible Cobalt-Cobalt Bridging By A Hemiacetal In The Dinuclear Cobalt Complex Bearing The Ligand Bis(3-(2-Pyridylmethyleneamino)Phenyl) Sulfone, Armando M. Guidote Jr, Tomoko Imajo, Yasuhiko Kurusu, Yoshiro Masuyama

Chemistry Faculty Publications

A dinuclear cobalt complex bearing the ligand bis(3-(2-pyridylmethyleneamino)phenyl) sulfone (BPMAPS) was prepared. It is proposed that the structure of this is [Coz(BPMAPS)(m-0AcMhemi-Et)]PF6 wherein the cobalt centers are bridged by two carboxylato groups in m-fashion and a hemiacetal with an ethoxy group (hemi-Et). This proposal is based on the similarity of the FT-IR, UV-Vis, and FAB-MS results with the crystallographically characterized dinuclear manganese complex [Mn2(BPMAPS)(m-OAcMhemi-Me)]PF6, and elemental analysis results.

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Rapid Determination Of Serum Melatonin By Esi–Ms–Ms With Direct Sample Injection, Shuming Yang, Xiaohui Zheng, Yan Xu, Xiang Zhou Oct 2002

Rapid Determination Of Serum Melatonin By Esi–Ms–Ms With Direct Sample Injection, Shuming Yang, Xiaohui Zheng, Yan Xu, Xiang Zhou

Chemistry Faculty Publications

This paper describes a rapid, simple and sensitive analytical method for the quantitative determination of melatonin in human serum by ESI–MS–MS with direct serum sample injection and on-line extraction. The method uses N-acetyltryptamine as the internal standard. It has high specificity and sensitivity for serum melatonin analysis. The internal calibration curve shows a wide linear range from 0.500 to 200 ng/ml with a correlation coefficient, R2>0.999. The limit of quantitation is 0.500 ng/ml and the limit of detection is 0.100 ng/ml with 10-μl sample injection. The recoveries of serum melatonin at three levels are approximately 70%. The intra-assay precision …

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Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu Oct 2001

Simultaneous Determination Of Enantiomers Of Structurally Related Anticholinergic Analogs In Human Serum By Liquid Chromatography–Electrospray Ionization Mass Spectrometry With On-Line Sample Cleanup, Vladimı́R Čápka, Yan Xu

Chemistry Faculty Publications

Trihexyphenidyl, biperiden and procyclidine are anticholinergic drugs produced as racemates for the treatment of Parkinson’s disease. This paper describes a simple and sensitive LC–MS method for the simultaneous determination of these compounds in human serum. An on-line sample clean-up procedure was used, where serum samples were directly injected into a “restricted-access media” pre-column. After the exclusion of the serum proteins, the drug molecules were eluted to a β-cyclodextrin analytical column for chiral separation. The quantitation was done by electrospray ionization MS using diphenidol as an internal standard. The method developed has limits of detection of 1 ng/ml, at least two-orders-of-magnitude …

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Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu Apr 2001

Determination Of Lysophosphatidic Acids By Capillary Electrophoresis With Indirect Ultraviolet Detection, Yi Lung Chen, Yan Xu

Chemistry Faculty Publications

Lysophosphatidic acid (LPA) is the simplest form of lysophospholipid. Molecular species of LPA have been identified as the potent components in the ovarian cancer activation factor. The elevated plasma LPAs may be used as potential biomarkers for the early detection of ovarian cancer. This paper is the first report on the quantitative analysis of molecular species of LPA using capillary electrophoresis. In this work, the separation of LPAs was achieved within 14 min in an adenosine monophosphate-borate–methanol–water solution, and the measurement was accomplished by indirect UV detection. With LPA (D) as internal standard, the method had linear calibration ranges for …

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Stereoselective Determination Oftrihexyphenidyl In Human Serum By Lc–Esi–Ms, Vladimı́R Čápka, Yan Xu, Yong Hong Chen Nov 1999

Stereoselective Determination Oftrihexyphenidyl In Human Serum By Lc–Esi–Ms, Vladimı́R Čápka, Yan Xu, Yong Hong Chen

Chemistry Faculty Publications

The antiparkinsonian drug trihexyphenidyl (THP) is currently manufactured and administered as a racemate. However, stereochemistry can play significant role in the drug’s pharmacokinetics, biotransformation, metabolism, interaction with cellular and tissue components and overall effect on human body. It is necessary to consider such a drug as a mixture of two compounds (drug enantiomers), with their own effect on the human body. The present paper describes a simple and sensitive LC–MS method for the stereoselective determination of THP in human serum. In this study, the sample was prepared by a solid-phase extraction (SPE) procedure. The enantiomer separation was done using native …

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Enhancing The Performance Of Membrane Introduction Mass Spectrometry By Organic Carrier And Liquid Chromatographic Separation, Shi Ouyang, Yong Hong Chen, Yan Xu Jan 1997

Enhancing The Performance Of Membrane Introduction Mass Spectrometry By Organic Carrier And Liquid Chromatographic Separation, Shi Ouyang, Yong Hong Chen, Yan Xu

Chemistry Faculty Publications

A method of membrane introduction mass spectrometry with liquid chromatographic separation (LC/MIMS) for the analysis of volatile organic compounds (VOCs) in water has been developed. The method not only inherited all the advantages of membrane introduction mass spectrometry by flow-injection analysis (FIA/MIMS), but also expanded the application of MIMS to the determination of compounds with identical quantitation ions. Because the quantitation by LC/MIMS is based on two-dimensional identification (retention time (tr) and mass-to-charge ratio ()), it provides a tangible approach to the analysis of VOCs in complex aqueous samples. In this work, a C18 column and a mobile phase (methanol/water) …

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Indirect Ultraviolet Detection Of Biologically Relevant Organic Acids By Capillary Electrophoresis, Hong Chen, Yan Xu, Frederick Van Lente, Michael P.C. Ip Apr 1996

Indirect Ultraviolet Detection Of Biologically Relevant Organic Acids By Capillary Electrophoresis, Hong Chen, Yan Xu, Frederick Van Lente, Michael P.C. Ip

Chemistry Faculty Publications

Indirect UV detection of fourteen short-chain organic acids (e.g., oxalic acid, citric acid, malonic acid, tartaric acid, methylmalonic acid, α-ketoglutaric acid, succinic acid, ethylmalonic acid, methylsuccinic acid, glutaric acid, apidic acid, methylglutaric acid, lactic acid and pyruvic acid) by capillary electrophoresis is described. The method used phthalate as the UV-absorbing additive in carbonate buffer and the non-absorbing analytes were detected indirectly at 230 nm. The influences of buffer pH, ionic strenght, concentration of phthalate and organic modifier on indirect signal response and migration behavior of the organic acids were investigated. Comparisons of reproducibility on migration time, limit of detection and …

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Electrochemical Enzyme Immunoassay Using Sequential Saturation Technique In A 20-Μl Capillary: Digoxin As A Model Analyte, Noriaki Kaneki, Yan Xu, Anu Kumari, H. Brian Halsall, William R. Heineman, Peter T. Kissinger Mar 1994

Electrochemical Enzyme Immunoassay Using Sequential Saturation Technique In A 20-Μl Capillary: Digoxin As A Model Analyte, Noriaki Kaneki, Yan Xu, Anu Kumari, H. Brian Halsall, William R. Heineman, Peter T. Kissinger

Chemistry Faculty Publications

Capillary enzyme immunoassay with flow-injection analysis for digoxin using the sequential saturation technique has been developed. Glass capillary tubes (10 cm × 0.53 mm i.d.) with immobilized digoxin antibody were used as the immunoassay reactor. The product of enzymatic reaction. 4-aminophenol, was detected amperometrically. The digoxin and the labeled digoxin binding reaction with the immobilized digoxin antibody were completed in 2 and 10 min, respectively. Digoxin was determined in a 20-μl sample with a detection limit of 10 pg ml−1 (200 fg or 260 attomoles) and a 3 orders of magnitude range.

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Solid-Phase Electrochemical Enzyme Immunoassay With Attomole Detection Limit By Flow Injection Analysis, Yan Xu, H. Brian Halsall, William R. Heineman Jan 1989

Solid-Phase Electrochemical Enzyme Immunoassay With Attomole Detection Limit By Flow Injection Analysis, Yan Xu, H. Brian Halsall, William R. Heineman

Chemistry Faculty Publications

A sandwich electrochemical enzyme immunoassay with flow injection analysis for the model antigen mouse IgG has been developed with alkaline phosphatase as the enzyme label. The enzyme substrate, 4-aminophenyl phosphate and its enzymatic reaction product, 4-aminophenol have been studied by cyclic and hydrodynamic voltammetry. The determination of 4-aminophenol by flow injection analysis with electrochemical detection (FIAEC) has a linear range of 5.0 × 10−8 to 1.0 × 10−5 M, a detection limit of 2.4 × 10−8 M, and a sample throughput of 72 samples/h. The detection limit is set by a background capacitance response, which depends on the ionic strength …

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