Current Organic Chemistry - Volume 14, Issue 19, 2010

This special issue of Current Organic Chemistry is devoted to “Recent advances in chemical analysis of organic compounds”. Organic compounds, synthetic semi-synthetic or natural are often associated with basic processes of life, such as carbohydrates, proteins,nucleic acids, lipids. They can be found in different matrices including environmental samples, food, human biological fluids,pharmaceuticals etc. Their determination is beyond any reasonable doubt of paramount importance. By a quick glance at the literature various techniques and numerous methods can be found. Recent advances in the chemical analysis of some selected compounds are presented in this thematic issue providing information from a cutting-edge research conducted by the most dynamic scientists, experts in their scientific field. Ten review articles are presented following the regular procedure of peer-review. The first review focuses on applications of specific chemical reactions for the development of novel instrumental analytical methods in chromatography-mass spectrometry. It covers the commercial instrumentation based on specific reactions of analytes in the gas phase such as the chemical reaction interface-mass spectrometry as a universal detector for (gas, liquid and size-exclusion) chromatographic separation, the ion-molecule reaction mass spectrometry for analysis of gases and proton-transfer reactions for volatile organic compounds. Recent development of a novel technique based on exclusive/selective reactions of chemical noise ions with chosen neutral reagents for the reduction of the chemical background interference in LC-MS has also been reviewed. A selection of examples of novel chemical derivatization such as inorganic fluoride analysis using GC or HPLC after conversion into organic species is also included together with a discussion on the contribution and the disadvantages of these techniques compared to other conventional instrumentations. Another contribution covers the advances in liquid chromatographic separation and the detection of underivatized amino acids. In this review the problems associated with the liquid chromatographic analysis of underivatized amino acids are identified and, through reviewing the recent literature, possible solutions are described. The advantages offered by preliminary voltammetric studies at microelectrodes (under mass transfer conditions similar to those of a flow cell detector) in optimising the operation of amperometric detectors are discussed and the use of environmentally friendly Bi electrode materials for the stripping voltammetric determination of aminoacids is also proposed. A broad outline of the potential of improvement of separation of underivatized amino acids by using multimode gradient elution and/or ionchromatography, provided that the relevant separation theory and optimization algorithms are available, is also discussed. Since the environment emerges as an important field for analytical methods, a review on the recent advances in modern extraction techniques for the determination of organic pollutants in environmental matrices remains of paramount importance. One or more pretreatment steps before instrumental analysis known as “sample preparation” is still mandatory in many applications, for enrichment, cleanup, and signal enhancement. Sample preparation is a very important and essential step in environmental analysis. Modern trends in sample preparation are towards faster, greener, solvent-less and inexpensive extraction techniques. Another contribution presents a brief overview of modern sample preparation such as solvent based methods, sorptive, membrane - assisted and instrumental methods which have been recently applied to extract and preconcentrate organic pollutants from different environmental matrices. The different requirements of each methodology (and its modes of implementation), especially the extraction phase, are discussed. There is also a presentation of selected examples involving novel analytical approaches for extraction of organic contaminants to evaluate the merits of the various techniques on the basis of published data for real-life analysis of environmental matrices. Analytical methods exploring the 5th base in DNA are presented in another contribution. Many technologies have been developed so as to evaluate DNA methylation, but the accurate and reproducible quantification of DNA methylation remains challenging. The ‘gold-standard’ for determining and quantifying the methylation state of a genomic region at single-nucleotide resolution is sequence analysis after bisulphite conversion. The main drawbacks in this approach are the fact that the conversion reaction is frequently incomplete and the clonal sequencing subsequently required is costly, time consuming and dependent on the heterogeneity of DNA methylation. Thus, a large number of clones must be sequenced for each PCR amplicon for accurate representation of the DNA methylation profile. In this review there is a presentation of novel approaches for high-throughput DNA methylation by application of analytical methods especially high pressure liquid chromatography (HPLC), liquid chromatography coupled with mass spectrometry (LC-MS) and matrix-assisted laser desorption/ionization time-of flight mass spectrometry (MALDI-TOF MS). Recent developments in sample pretreatment, separation and hyphenated atomic and mass spectrometric techniques for organoselenium speciation in biological liquids is the subject of another contribution. Since organoselenium species like selenoaminoacids, selenopeptides, alkylselenides etc. and also selenite (SeIV) and selenate (SeVI) ions are known to be present in biological liquids and tissues, some of which playing a very active role, there is a constant trend to develop or improve current analytical methodologies in order to enable species-specific detection and determination of these species in biological samples. Recent developments reported during the last decade and referring to the application of modern hyphenated techniques based on atomic or mass spectrometric detectors are reviewed. The available information is classified according to the sample pre-treatment procedures applied, the separation techniques and the detectors used. The research and development of electrochemical biosensors applied to life sciences during the past years were reviewed in another article. In the first part a brief introduction on nanomaterial based electrochemical DNA biosensors is given. In the second part DNA biosensors and transition metal complexes with biological interest are described. Finally, the development trends of electrochemical biosensors in genetic and epigenetic testing are discussed. The use of monolithic columns in the HPLC analysis of organic compounds was the subject of another review. The increasing demand for ultra-fast separations has motivated the development of new materials in the field of chromatographic stationary phases. Since High Performance Liquid Chromatography is a powerful and popular technique, the importance of improving existing supports, as well as the development of new types of columns is more than profound. The advent of monolithic columns offers new practical possibilities for decreasing retention times and/or increasing column efficiencies. The transfer of existing methods at similar or higher flow rates has been studied by various researchers. A considerable gain in time has been noticed compared with similar conditions on classic columns. Applications of monoliths as stationary phases include pharmaceuticals, biofluids, food matrices, environmental samples, biochemical species, proteomics etc. Several additional application modes of monolithic columns have been explored. Dental composites are tooth filling materials. Their chemical composition is complex since they are composed of synthetic polymers, ceramic reinforcing fillers, molecules which promote or modify the polymerization reaction that yields the cross-linked polymer matrix from the dimethacrylate resin monomers, and silane coupling agents which enable bonding of the reinforcing fillers to the polymer matrix. Each of these components is critical for a successful dental restoration. Residual monomers in the resin matrix such as triethylene glycol dimethacrylate (TEGDMA), bisphenol A glycerolate dimethacrylate (BisGMA), and urethane dimethacrylate (UDMA), additives and degradation products from resin-based dental restorative materials eluted into the oral cavity may influence the biocompatibility of these materials. The analysis of eluted compounds from dental materials requires reliable quantification methods useful for studies addressing cytotoxic, genotoxic and estrogenic potential of these substances. In this review recent chromatographic methods developed for the determination: i.e. Quantification and identification of components released from dental composites in saliva and other biological fluids have been presented critically. Differences in stereochemistry can influence the pharmacological, metabolic or toxicological activity of drug formulations. In other words isomer specific pharmaceuticals often exhibit increased potency, higher bioavailability and reduced side effects when compared to racemic pharmaceutical compounds. The development of new practical methods for the preparation of enantiomerically pure substances is thus vital and nowadays, pharmaceutical industry demand detailed investigations of chiral molecules, in compliance with the regulatory requirements. One contribution focuses on the most important methods developed for the enantiomeric resolution by high pressure liquid chromatography. The mechanisms of the different separation principles are briefly discussed. Also the major chiral stationary phases, commercially available, are presented, including a guide provided to help the readers select the appropriate chiral stationary phase. Last but not least, the analysis of organic impurities of active pharmaceutical ingredients and formulations is covered by an interesting review dedicated to the recent developments in the field of analytical chemistry concerning the determination of impurities which may arise during the manufacturing process or storage of a formulation including starting materials and excipients, by-products and degradation products, reagents and catalysts. The potentials and recent applications of a variety of analytical techniques on this area are described and discussed. Emphasis is given to separation techniques that are the most widely used under both academic and industrial environment (liquid chromatography, capillary electrophoresis, micellar electrokinetic chromatography, etc.) and mass spectrometry (including LC-MS). As guest editor of this special issue, I would like to express my appreciation to all contributors for their imperative work, as well as to the referees for their assistance to achieve review articles of high quality. I hope that the aim of this special thematic issue to point out the state-of-the-art of organic compounds analysis in various analytical fields has been fulfilled and that the readers will benefit from this issue, by enjoying it as well as by gathering significant information for their field of scientific interest and expertise

Taking the advantages of the chemical conversion of analytes through chemical reactions either in the solution or gas phase, very often an instrumental analytical problem can be addressed in a completely different way. This is at large due to the involvement of the chemical resolution in instrumental analysis. This review is focused specifically on contributions of chemical reactions to the development of novel instrumental analytical techniques in chromatography-mass spectrometry in the past two decades. It covers first the commercial instrumentations based on chemical reactions of analytes in the gas phase such as chemical ionization in gas chromatography- mass spectrometry (GC-MS), atmospheric pressure chemical ionization in liquid chromatography-mass spectrometry (LC-MS), proton- transfer reaction GC-MS for volatile organic compounds, and chemical reaction interface-mass spectrometry as a universal detector for GC, LC and size-exclusion chromatography (SEC) separation. Additionally, the recent development of a novel technique based on selective reactions of chemical noise ions with chosen neutral reagents for the reduction of chemical background noise in LC-MS trace analysis is also reviewed. The contribution of ion-molecule reactions to each instrumentation and their applications compared to other conventional techniques will be discussed.

The problems associated with liquid chromatographic analysis of underivatized amino acids are identified and, through reviewing the recent ten years literature, possible solutions are described. Emphasis has been placed on amperometric as well as on multi mode detection. The advantages offered by preliminary voltammetric studies at microelectrodes (under mass transfer conditions similar to those of a flow cell detector) in optimising the operation of amperometric detectors are discussed and the use of environmentally friendly Bi electrode materials for the stripping voltammetric determination of amino acids is also proposed. This review is also aimed at giving a broad outline of the potential for improvement of the separation of underivatized amino acids offered by multimode gradient elution and/or ion-chromatography provided that the relevant separation theory and optimization algorithms are available.

Sample preparation is a very important and essential step in environmental analysis. A brief overview of modern sample preparation such as solvent based methods, sorptive, membrane - assisted and instrumental methods which have been recently applied to extract and preconcentrate organic analytes from different environmental matrices, is presented. The different requirements of each methodology (and its modes of implementation), especially the extraction phase, are discussed. Instead of a comprehensive list of applications, the implementation of these techniques with selected examples covering mainly research published the last three years is highlighted.

Expression of genetic information is related to the presence of 5-methylcytosine in DNA. The distribution of 5-methylcytosine varies in different tissues and its frequency is drastically modified according to the developmental stage of the cell as well as under pathological conditions. Among other applications, the presence of &ldquoirregular&rdquo 5-methylcytosine distribution is currently used as a marker of carcinogenesis as well as of abnormal neurological and other pathological conditions. Analysis of the distribution and mostly the frequency of this modified base, applying an accurate and reproducible method, is a challenge, frequently met by the application of various methods involving the use of analytical techniques. In this review we present the high-throughput analysis of DNA methylation by High Performance Liquid Chromatography, Denaturing High Performance Liquid Chromatography and Gas Chromatography. Moreover, we discuss in detail the principles, as well as the advantages and disadvantages of the above methods, their application for analyzing either global or gene-specific methylation and the biological issues addressed in these studies. In addition, we discuss the detection, by the same methods, of other minor DNA bases, besides 5- methylcytosine, as well as the choice of base derivatives monitored in these studies. Finally, we present information regarding the evaluation of analytical data relative to those obtained by molecular techniques and discuss the particular clinical applications for which the use of analytical techniques can be particularly valuable.

Since organoselenium species like selenoaminoacids, selenopeptides, alkylselenides etc. and also the inorganic species selenite (Se (IV)) and selenate (Se (VI)) are known to be present in biological liquids and tissues, some of them playing an important role, there is a constant demand to develop or improve current analytical methodologies in order to enable species-specific detection and determination of these species in biological samples. The availability of various atomization techniques in atomic spectrometry and also of various ionization techniques in mass and tandem mass spectrometry have significantly increased the analytical armoury for organoselenium speciation. The literature in this field is abundant and fast growing, thus in this review only recent developments reported during the last decade and referring to the application of modern hyphenated techniques based on atomic or mass spectrometric detection are reviewed. The available information is classified according to the sample pretreatment procedures applied, the separation techniques and detectors used.

The research and development of electrochemical biosensors applied to life sciences during the past years were reviewed in the present article. In the first part of the article, a brief introduction on nanomaterial based electrochemical DNA biosensors is given. In the second part DNA biosensors and transition metal complexes with biological interest are described. Finally, the development trends of electrochemical biosensors in genetic and epigenetic testing are being discussed.

The increasing demand for ultra-fast separations has motivated the development of new materials in the field of chromatographic stationary phases. Since High Performance Liquid Chromatography is a powerful and popular technique, the importance of improving existing supports, as well as the development of new types of columns is more than profound. The advent of monolithic columns offered new practical possibilities for decreasing retention times and/or increasing column efficiencies, while pressure restriction was significantly eliminated. Monolithic columns are prepared by means of a polymerization process from either organic polymers, such as polymethacrylates, polystyrenes or from inorganic polymers, such as silica. Highly porous rods of silica with a bimodal pore structure consist of macropores and mesopores. The former consist of a dense network of pores, while the latter form contain fine porous structure of the column. This structure dictates the major chromatographic features of monolithic columns. Since many analytical methods employing conventional columns already exist, it is very challenging to study their transfer at similar or higher flow rates using monolithic rods with a considerable gain in time. Applications of analytical methods in organic analysis employing monoliths as stationary phase include pharmaceuticals, biofluids, food matrices, environmental samples, biochemical species, proteomics etc. Several additional application modes of monolithic columns have been explored. An emergence of applications is expected to continue as long as more experience is gained with monolithic column technology. Such an attempt has been prompted also by the need of reduction in organic solvent consumption, in the frame of environmental friendly methods.

Dental composites are tooth filling materials. Their chemical composition is complex since they are composed of synthetic polymers, ceramic reinforcing fillers, molecules, which promote or modify the polymerization reaction that yields the cross-linked polymer matrix from the dimethacrylate resin monomers, and silane coupling agents, which enable bonding of the reinforcing fillers to the polymer matrix. Each of these components is critical for a successful dental restoration. Residual monomers in the resin matrix such as triethylene glycol dimethacrylate (TEGDMA), Bis-phenol A glycidyl dimethacrylate (BIS-GMA), and urethane dimethacrylate (UDMA), additives and degradation products from resin-based dental restorative materials eluted into the oral cavity may influence the biocompatibility of these materials. The determination of compounds eluted from dental materials in biological fluids is of utmost importance and requires reliable quantification methods useful for studies addressing cytotoxic, genotoxic and estrogenic potential of these substances. In this review recent chromatographic methods developed for the determination: i.e. quantification and identification of components released from dental composites in saliva and other biological fluids will be presented.

In recent years there has been considerable interest in the synthesis and separation of enantiomers of organic compounds especially because of their importance in the biochemistry and pharmaceutical industry. Major differences in biological activity have been observed in chiral molecules. These differences in stereochemistry can influence the pharmacological, metabolic or toxicological activity of the finished drug formulations. In other words isomer specific pharmaceuticals often exhibit increased potency, higher bioavailability and reduced side effects when compared to racemic pharmaceutical compounds. The development of new practical methods for the preparation of enantiomerically pure substances is thus vital and nowadays, pharmaceutical industry demands detailed investigations of chiral molecules, in compliance with the regulatory requirements. In this review some of the most important methods developed for the enantiomeric resolution by high pressure liquid chromatography, from the last decade, are described. The mechanisms of the different separation principles are briefly discussed. Also the major chiral stationary phases, commercially available, are presented, including a guide provided to help the readers selecting the appropriate chiral stationary phase. Finally the most common chiral selectors used as additives in mobile phases are described, including their advantages and their limitations.

Impurity profiling of active pharmaceutical ingredients is a critical quality control parameter during all stages of the development, production and stability testing of pharmaceutical formulations. Literature on this is continuously increasing, it is therefore important to keep track on the latest achievements and applications. This review presents an overview of the most recently published results on the analysis of organic impurities in pharmaceutical samples and active ingredients. Special attention is given to the most widely used techniques, such as liquid chromatography, capillary electrophoresis and mass spectrometry.