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Van Schoors J.,Vrije Universiteit Brussel | Brouwer H.-J.,Antec | Maes K.,Vrije Universiteit Brussel | Michotte Y.,Vrije Universiteit Brussel | Van Eeckhaut A.,Vrije Universiteit Brussel
Journal of Chromatography A | Year: 2013

The use of ion-pair ultra-high performance liquid chromatography (UHPLC) coupled with electrochemical detection (ECD) is of great interest for the fast and sensitive determination of the monoamine neurotransmitters dopamine, noradrenaline and serotonin in microdialysis samples. However, when applying high flow rates in ion-pair UHPLC, other peaks than the initial compound peaks appear on the chromatogram. This peak-splitting phenomenon is caused by disturbed ion-pair retention mechanisms. The influence of several chromatographic parameters is investigated. Peak-splitting is delayed to higher flow rates when increasing the concentration of ion-pair reagent or buffering agent in the mobile phase, when decreasing the percentage of organic modifier in the mobile phase, when applying a stationary phase with a smaller amount of packing material or when increasing the separation temperature. One or a combination of these conditions can be applied to analyze the monoamine neurotransmitters using ion-pair UHPLC-ECD at high flow rates. © 2013 Elsevier B.V.

Oberacher H.,Innsbruck Medical University | Erb R.,Innsbruck Medical University | Plattner S.,Innsbruck Medical University | Chervet J.-P.,Antec
TrAC - Trends in Analytical Chemistry | Year: 2015

Oxidation reactions play a major role in the modification of nucleobases in DNA and RNA. Enzymatic oxidation reactions are involved in the control of epigenetic signaling as part of DNA-demethylation pathways. Oxidative stress gives rise to non-enzymatic oxidation. Many different oxidative DNA modifications have been identified. The cellular responses to such oxidative damage involve several processes, such as DNA repair, cell-cycle arrest and apoptosis. Persistent DNA damage may result in genomic instability, which is considered to play a role in the development of cardiovascular and neurological diseases, aging and cancer. Due to the involvement of nucleic-acid oxidation in many biological processes, understanding the underlying mechanisms is of the utmost importance. Herein, we demonstrate the vast potential of electrochemistry coupled to liquid chromatography-mass spectrometry as a tool for studying the oxidative stability of nucleic-acid species and identifying important oxidation products. © 2014 Elsevier B.V.

Plattner S.,Innsbruck Medical University | Erb R.,Innsbruck Medical University | Pitterl F.,Innsbruck Medical University | Brouwer H.-J.,Antec | Oberacher H.,Innsbruck Medical University
Journal of Chromatography B: Analytical Technologies in the Biomedical and Life Sciences | Year: 2012

Chemicals can interact with the genetic material giving rise to the formation of covalent adducts. These alterations can lead to adverse consequences, including cancer, reproductive impairment, development anomalies, or genetic diseases. In search for an assay allowing identification of hazardous compounds that might form covalent adducts with nucleic acids, electrochemistry (EC)/liquid chromatography (LC)/mass spectrometry (MS) is presented. EC/LC/MS is a purely instrumental approach. EC is used for oxidative activation, LC for the fractionation of the reaction mixture, and MS for the detection and characterization of the reaction products. To test the system capabilities, we investigated the formation of covalent adducts produced by guanosine and acetaminophen (APAP). Electrochemical activation of mixtures of guanosine and APAP gave rise to the formation of four isomers of (guanosine. +. APAP-2H). Mass voltammograms as well as dose-response-curves were used to obtain insights in the mechanism of adduct formation. These experiments revealed that a mechanism involving radical intermediates is favored. The initial step of adduct formation is the conversion of both APAP and guanosine into radicals via one-electron-one-proton reactions. Among different competing reaction pathways, the generated radical intermediates undergo intermolecular reactions to form covalent adducts between guanosine and APAP. © 2011 Elsevier B.V.

Plattner S.,Innsbruck Medical University | Erb R.,Innsbruck Medical University | Chervet J.-P.,Antec | Oberacher H.,Innsbruck Medical University
Analytical and Bioanalytical Chemistry | Year: 2012

Electrospray ionization (ESI) involves the dispersion of a liquid containing analytes of interest into a fine aerosol by applying a high potential difference to the sample solution with respect to a counter electrode. Thus, from the electrochemical point of view, the ESI source represents a two-electrode controlled-current electrochemical flow cell. The electroactive compounds part of the solvent sprayed may be altered by occurring electrolysis (oxidation in positive ion mode and reduction in negative ion mode). These reactions can be troublesome in the context of unknown identification and quantification. In the search for a simple, inexpensive, and efficient way to suppress electrochemical oxidation in positive ESI, the usability of ascorbic acid, hydroquinone, and glutathione for homogenous redox buffering was tested. Performance of the antioxidants was assessed by analyzing pharmaceutical compounds covering a broad range of functional groups prone to oxidation. Different emitter setups were applied for continuous infusion, flow injection, and liquid chromatography/mass spectrometry experiments. Best performance was obtained with ascorbic acid. In comparison to hydroquinone and glutathione, ascorbic acid offered superior antioxidant activity, a relatively inert oxidation product, and hardly any negative effect on the ionization efficiency of analytes. Furthermore, ascorbic acid suppressed the formation of sodiated forms and was able to induce charge state reduction. Only in the very special case of analyzing a compound isobaric to ascorbic acid, interference with the low-abundant [ascorbic acid+H]+ signal may become a point of attention. © 2012 The Author(s).

Jones R.E.,Antec
Plastics Engineering | Year: 2010

The conditions prevailing in the economy of the US after facing the challenges of economic recession are discussed. It has been observed that the economic recession has adverse impact on the overall GDP growth of the country and its plastics industry. The domestic manufacturing industry, including the plastics sector, is facing challenges of recovering from the adverse impacts of economic recession due to the implementation of stringent environmental regulations by several states in the country. The federal government is planning to increase its control over major sectors of the economy, ranging from banking, automobile companies, and healthcare within a year. The US Congress is planning to discontinue the tax discounts to companies after they expire in 2010, while increasing tax rates and adopting new taxes. These new taxes will include a value added tax similar to those used in Europe.

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