Frank-Michael Matysik

Voltammetric and sonovoltammetric studies on the oxidation of thymine and cytosine at a glassy carbon electrode

Abstract The voltammetric behaviour of the pyrimidine bases thymine and cytosine is studied using a glassy carbon electrode. In contrast to previous reports that assume electroinactivity at carbon electrodes, it is demonstrated that both compounds undergo well-defined oxidation at a glassy carbon electrode. The experimental conditions that influence the electrode reaction, in particular the pH of the electrolyte solution, are varied systematically and optimized for voltammetric determinations. The application of ultrasound in combination with differential pulse voltammetry results in a reliable analytical procedure for thymine and cytosine measurements avoiding electrode fouling and maintaining the electrode characteristics. The effect of ultrasound is mainly to enhance transport of electroactive species and to clean the electrode in situ. Besides studying the sonovoltammetric behaviour of cytosine and thymine separately, simultaneous determinations are also performed and extended to the analysis of adenine, guanine, thymine and cytosine in the same solution.

Recent advances in high resolution scanning electrochemical microscopy of living cells – A review

This review discusses advances in the field of high resolution scanning electrochemical microscopy (HR-SECM) and scanning ion conductance microscopy (SICM) to study living cells. Relevant references from the advent of this technique in the late 1980s to most recent contributions in 2012 are presented with special discussion on high resolution images. A clear progress especially within the last 5 years can be seen in the field of HR-SECM. Furthermore, we also concentrate on the intrinsic properties of SECM imaging techniques e.g. different modes of image acquisition, their advantages and disadvantages in imaging living cells and strategies for further enhancement of image resolution, etc. Some of the recent advances of SECM in nanoimaging have also been discussed which may have potential applications in high resolution imaging of cellular processes.

Sonoelectrochemical studies of guanine and guanosine

Abstract The voltammetric behaviour of the purine base guanine and the corresponding nucleoside guanosine at a glassy carbon electrode was investigated with the help of ultrasound. The adsorption of guanine and guanosine as well as the adsorption of their oxidation products affects the overall voltammetric characteristics dramatically. In particular, the effect of ultrasound on the simultaneous adsorption of guanine and guanosine was studied in detail. Quantitative sonovoltammetric experiments show the number of electrons involved in the electro-oxidation of guanosine to be two. Sonovoltammetry, i.e. the combination of voltammetry and ultrasonic irradiation, is demonstrated to be a useful approach to control the extent of adsorption of the relevant species and to avoid electrode fouling. This allows the development of reliable analytical procedures for the determination of guanine and guanosine, which are described in detail.

Improved end-column amperometric detection for capillary electrophoresis

Abstract An amperometric detector for end-column detection in capillary electrophoresis is described. The influence of the high voltage on the detection performance is studied. As a consequence of these studies it is shown that the end-column detection strategy operates up to capillary dimensions of 50 μm I.D. without using any electrical-field decoupler desig. The shift of the working electrode potential resulting from the presence of the high voltage electrical field is compensated by selecting a more positive potential setting via the potentiostat. The detector performance is characterized in terms of attainable separation efficiencies (300 000 theoretical plates for homovanillic acid), limits of detection (5·10 −8 mol/l for serotonin) and coulometric efficiencies (8.9% for homovanillic acid). Practical aspects associated with the use of microdisk electrodes instead of carbon fiber electrodes are addressed.

Nafion-coated mercury thin film electrodes for batch-injection analysis with anodic stripping voltammetry.

Batch-injection analysis exhibits the advantages of rapid and simple electroanalysis of microlitre samples. Nafion-coated mercury thin film electrodes have been evaluated for use in batch-injection analysis with anodic stripping voltammetry (BIA-ASV). The advantages of Nafion-coated electrodes in reducing electrode contamination by components of complex matrices are combined with the analysis of small microlitre sample volumes. The measurement of traces of lead and cadmium is used to illustrate the approach. An optimised procedure for formation of Nafion-coated mercury thin film electrodes is evolved. The relative sensitivity for BIA-ASV at electrodes with and without Nafion coatings is 0.9 and 0.8 for cadmium and lead respectively; detection limits are 2 x 10(-9) M and 4 x 10(-9) M. Studies were done concerning the influence of surfactants and their effect was found to be much less with the Nafion film coating. Applications to real environmental samples are demonstrated.

Detection of arsenic-containing hydrocarbons in canned cod liver tissue

Arsenic is a metalloid well known to be potentially toxic depending of its species. Lipid-soluble arsenicals (arsenolipids) are present in a wide range of biological samples in which they could play a role in the biosynthesis of organoarsenic compounds from inorganic arsenic compounds. Arsenolipids have recently attracted considerable interest. In order to gain deeper insights into the impact of arsenolipids new analytical approaches for reliable determination of this class of arsenic-containing hydrocarbons in various matrices are needed. High concentrations of arsenolipids were found in seafood which served as sample material in this study. We report the investigation of three arsenolipids found in canned cod liver from which they were extracted and purified by solid phase extraction (SPE) using a silica gel column and ethyl acetate/methanol as eluent. Analytical studies were conducted by means of gas chromatography coupled with ICP-MS, MIP-AES and EI-qMS and by TOF-MS. The results obtained by GC-ICP-MS and GC-MIP-AES showed the existence of numerous arsenic compounds in the SPE fractions collected. Three major peaks were found within a retention time window between 10 and 25 min. The presence of arsenic compounds in the fish tissue could be confirmed using GC-EI-qMS analysis. Corresponding information of the molecular weights of the major arsenic species were provided by TOF-MS which allows highly accurate mass determinations. The results showed the presence of the arsenic-containing hydrocarbons with the following molecular formulas: C(17)H(37)AsO (calculated for [M+H](+) 333.2133; found 333.2136; Deltam=0.90 ppm); C(19)H(41)AsO (calculated for [M+H](+) 361.2446; found 361.2446; Deltam=0.00 ppm); C(23)H(37)AsO (calculated for [M+H](+) 405.2133; found 405.2145; Deltam=2.96 ppm). Suggestions for the corresponding structures are discussed.

Application of non-aqueous capillary electrophoresis with electrochemical detection to the determination of nicotine in tobacco.

Non-aqueous capillary electrophoresis with electrochemical detection (NACE-ED) was applied to the determination of nicotine. The measurements were performed using an acetonitrile-based buffer. Nicotine was shown to yield well defined voltammetric signals suitable for oxidative detection. The precision of NACE-ED regarding migration time and peak height for samples containing 8 micrograms/ml nicotine is expressed by relative standard deviations of 0.1% and 1.6%, respectively (n = 8). The limit of detection for nicotine was 13 ng/ml (286 fg). For nicotine determination in tobacco samples various solutions were studied regarding the extraction efficiency in an ultrasonic bath. The highest extraction efficiency was obtained using a solvent mixture consisting of acetonitrile-acetic acid-water (20:5:75, v/v). The results for nicotine determination in tobacco were evaluated using tobacco reference material with certified nicotine content. Analytical aspects such as accuracy, reproducibility and selectivity were addressed in this work. The measurements were based on the use of a newly developed electrochemical detector cell which was found to enable user-friendly operation of NACE-ED measurements.

Non-aqueous capillary electrophoresis with electrochemical detection

Abstract The application of electrochemical detection (ED) in conjunction with non-aqueous capillary electrophoresis (CE) is described. Using an acetonitrile-based buffer system only minor effects of the high voltage on the electrochemical detection circuit occur during CE experiments. Thus, for the first time CE–ED measurements are performed employing 75-μm I.D. capillaries without a special capillary modification or interruption. Capillaries from various sources are evaluated regarding their suitability for non-aqueous CE–ED. All fused-silica capillaries tested allow reproducible measurements. However, there are differences in separation efficiency depending on the fused-silica material used. The analytical characteristics of non-aqueous CE–ED are explored using ferrocene and (ferrocenylmethyl)trimethylammonium perchlorate ([FcMTMA]ClO4) as model analytes. The reproducibility of migration time and signal height is expressed by relative standard deviations of 0.18 and 1%, respectively (n=10). The limit of detection for [FcMTMA]ClO4 is 6×10−8 M. Practical applications concerning the determination of dye compounds such as malachite green, crystal violet and rhodamine B are discussed. A remarkably good stability of electrode response is observed for extended measuring periods owing to the well-defined surface characteristics of the platinum electrode in the acetonitrile-based medium.

Analytical methods for the determination of arsenosugars—A review of recent trends and developments

Arsenic-containing carbohydrates, generally termed arsenosugars, have been the subject of increasing analytical interest in arsenic speciation analysis. The present review gives an overview concerning achievements and trends in the field of instrumental analysis of arsenosugars. The typical experimental approaches for sample pre-treatment, extraction, separation and detection are discussed. Current possibilities and limitations of modern instrumental techniques are pointed out.

Electrochemical methods in conjunction with capillary and microchip electrophoresis

Electromigrative techniques such as capillary and microchip electrophoresis (CE and MCE) are inherently associated with various electrochemical phenomena. The electrolytic processes occurring in the buffer reservoirs have to be considered for a proper design of miniaturized electrophoretic systems and a suitable selection of buffer composition. In addition, the control of the electroosmotic flow plays a crucial role for the optimization of CE/MCE separations. Electroanalytical methods have significant importance in the field of detection in conjunction with CE/MCE. At present, amperometric detection and contactless conductivity detection are the predominating electrochemical detection methods for CE/MCE. This paper reviews the most recent trends in the field of electrochemical detection coupled to CE/MCE. The emphasis is on methodical developments and new applications that have been published over the past five years. A rather new way for the implementation of electrochemical methods into CE systems is the concept of electrochemically assisted injection which involves the electrochemical conversions of analytes during the injection step. This approach is particularly attractive in hyphenation to mass spectrometry (MS) as it widens the range of CE-MS applications. An overview of recent developments of electrochemically assisted injection coupled to CE is presented.