Current Analytical Chemistry - Volume 8, Issue 1, 2012

Current Analytical Chemistry now enters in its 8th year of publication. It has become a leading journal in its field with a respectable impact factor. I would like to thank the Associate Editors, Guest Editors, Regional Editors as well as the Editorial Board Members for their constant efforts and guidance. I am also grateful to the authors for their valuable contributions.

Soon after the word “proteome” was firstly coined by Marc Wilkins in 1994 to describe the sum of proteins produced by an organism or a biological system, the term “proteomics” was coined to define the large scale study of the proteome. Ever since then, especially after the completion of the draft sequence of the human genome, various “omics (or-omes)” terms have been created to signify the study of respective “–omes” at an amazing pace, which reflects a new omics era. Among a number of omics terms, genomics, transcriptomics, proteomics, metabolomics, and interactomics (large scale analysis of all the interactions among various biological components) have gained more and more popularity than others and are even reviving and boosting a very promising discipline of systems biology, which is the study of systems of biological components. Characterized by common features and analytical challenges from the point of view of current analytical chemistry, all these omics studies require highly sensitive and high throughput analysis of a very large number of components from a very complicated biological system. From another point of view of biological systems, proteomics, metabolomics and interactomics analysis is much more complicated than genomics and transcriptomics, because genome and transcriptome are more or less constant and are made of less number of “chemical units (DNA or RNA molecule)”, which has been reflected in the recent technological advances now allowing genomes or transcriptomes to be sequenced at a breathtaking speed by means of a large-scale, high throughput DNA sequencing platform or microarray technologies. It is well known that the completion of the draft sequence of the human genome was achieved over ten years ago, while the human proteome or metabolome are still far beyond the reach due to the inherent complexity, even with tremendous technological advances in the past ten years, let alone the much more complicated interactome. However, proteomics and metabolomics, which focus on a large-scale analysis of proteins and metabolites, are among the highly pursued goals in biomedical research. This mini Hot Topic Issue mainly addresses analytical challenges and the most recent advances in these two omics fields. Since proteomics and metabolomics analysis are highly dependent on a similar set of analytical tools, the most powerful liquid chromatography (LC) and mass spectrometry (MS) in the current analytical sciences. This special issue is thus aimed to provide state-of-the-art LC-MS based strategies for proteomics and metabolomics analysis, with an emphasis on its success in the biomedical or pharmaceutical applications. The technological advances in liquid chromatography coupled to mass spectrometry (LC-MS) have expended tremendously to the proteomics analysis with the discovery of electrospray ionization (ESI) method in the late 1980s by John Fenn which provided a highly compatible interface between LC and MS and was recognized by the award of the Nobel Prize for Chemistry in 2002. By combining the physical separation capability of LC with the universal mass analysis power of MS, LC-MS has become increasingly important in both proteomics and metabolomics due to its unparalleled capability in the mixture analysis with a high sensitivity and selectivity since then and continues to be the key and leading technology in omics with the continuously incremented developments in both LC separation and MS based detection. Nowadays, biomarker discovery, biomedical studies and biopharmaceutical industries rely heavily on the valuable information extracted from LC-MS based omics analysis. For current proteomics research, it has been shifted from conventional 2-D Gel and MS based analysis to various stable isotope labeled quantitative gel-free methods and more recently to gel-free and label-free LC-MS based strategies. Meanwhile, more and more interests in the proteomics analysis have changed its theme from global qualitative identification of proteins as many as possible to quantitative analysis of targeted protein post-translational modifications (PTMs), such as protein phosphorylation and glycosylation. To reflect these updated trends in proteomics, this issue has put more weight on both LC-MS based quantitative proteomics and phosphoproteomics which is a large-scale study of phosphorylated proteins, representing one of the most important protein post-translational modifications. As for metabolomics research, because it is a much more complicated analysis as compared to that of proteomics, up to now, the metabolomics research advance is so far behind proteomics. This issue also covers the most recent LC-MS based metabolomics progress in Panax ginseng research, which has implied the powerfulness and great promise in the application of MS-based metabolomics strategies to reveal the chemical components and pharmacological activity of ginseng in this special field. This mini- Hot Topic Issue will include four chapters (topics). A brief introduction to each Chapter (topic) will be illustrated as below. Phosphoproteomics is the large-scale study of protein phosphorylation, which is one of the most important protein PTMs and plays a central role in regulating a wide array of cellular signaling pathways from prokaryotes to eukaryotes. Quantitative phosphoproteomics is a rapidly growing, while challenging subject in proteomics research expanding our understanding of biology and diseases, because it has exhibited great promise for the discovery of new drug targets and biomarkers. Chapter 1, reviews the most recent developments in LC-MS based phosphoproteomics with an emphasis on quantitative phosphoproteomics and details the most up-to-date popular strategies in quantitative phosphoproteomics and the advantages and limitations of each method. This intensified review will not only serve as a quick guideline for mass spectrometrists who strive to develop tailored quantitative phosphoproteomics strategies for various research subjects, but also an informative introduction to scientists in related field, like biologists who may have a lot of interest in this very promising topic in proteomics....

Reversible protein phosphorylation is among the most widespread and important protein modifications in nature, regulating a vast number of key cellular signaling pathways, and deregulation of phosphorylation-mediated processes is often implicated in many human diseases including cancers. Large-scale qualitative and quantitative analysis of protein phosphorylation is thus essential for understanding these important cellular signaling pathways and their underlying mechanisms. This challenging task has been enabled by exciting progress in both effective phosphopeptide enrichment strategies and powerful liquid chromatography coupled to with mass spectrometry (LC-MS). This review will detail some of the most recent developments in LC-MS based phosphoproteomics with an emphasis on quantitative analysis of protein phosphorylation or quantitative phosphoproteomics. We discuss a variety of LC-MS based in vivo and in vitro stableisotope labeling and label-free methods for global quantitative phosphoproteomics, and briefly introduce the progress in targeted quantitative phosphoproteomics while highlighting the application of some up-to-date popular techniques with corresponding representative workflows. For each strategy, the benefits and drawbacks are compared and highlighted in order to aid scientists in tailoring the most appropriate strategy under various circumstances for the global or targeted analysis of protein phosphorylation pertinent to any biological or biomedical questions in their own research.

A number of stable isotope labeling techniques have been developed and have become the most prospective approaches in the realm of shotgun differential proteomics, where mass spectrometry is often coupled with liquid chromatography for better sensitivity, efficiency and specificity. Among these stable isotope labeling techniques, 18O labeling has received growing interest in the research community due to its simplicity and applicability. This review focuses on recent advances on methodologies regarding 18O labeling, such as the use of ultrasonic energy for rapid labeling, non-enzyme mediated 18O labeling, isotope precursors other than 18O water, and new tools for data processing, etc. Recent biological applications of 18O labeling on quantitative proteomics, especially profiling and quantifying several types of posttranslational modifications, are also discussed.

Liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS) is the primary method for sample analysis used in proteomics. The high-resolution separation of liquid chromatography (LC), coupled with the sensitivity and specificity of mass spectrometry (MS) permits the identification of thousands of peptides in a single analysis of protease digested samples. Although numerous advances have been made in recent years, there is still a long way to go to achieve the ultimate goal of proteomics-----the comprehensive characterization of all proteins, including post-translational modifications (PTM), irrespective of sample type and complexity. Due to the importance of protein phosphorylation in biological processes, its identification and quantification have become an intensely studied subset of proteomics. Phosphorylated peptides exhibit increased acidity and high affinity towards metal ions in comparison to other peptides. Therefore, special considerations should be taken when developing an LC-MS technique for phosphorylated peptide analysis. While advancements in instrumentation continue to increase the sensitivity, speed, resolution, and dynamic range of current mass spectrometers, the development of complementary LC methods has received less attention. In this communication, we will review the advancements in LC technology in proteomics, with a focus on the analysis of phosphorylated peptides.

This review summarizes the current status of mass spectrometry (MS)-based techniques used in ginseng research. The review has been explored from two parts. The first part presents an overview of the chemical analysis of ginseng based on MS and liquid chromatography-mass spectrometry (LC-MS), including the application of MS/MS on systematic structural characterization of ginsenosides and the fragmentation patterns of different metal adducts with ginsenoside for structure analysis, the characterization of ginsenosides in the crude extracts by LC-MS, the investigation of hydrolysis and changes of ginsenosides in ginseng and related prescription formula by LC-MS to provide the material basis for Traditional Chinese Medicine (TCM), and pharmacokinetics and metabolism studies of ginsenosides by LC-MS. The second part focuses on the dynamically developing field of MS-based metabolomics and its potential applications in ginseng related research. This includes the strategy of ginseng quality control in terms of chemical changes for both original herbs and their processed products by plant metabolic profiling to ensure proper preparation and standardization, and the mechanism study and biomarker discovery for understanding the holistic effects and synergistic activities of ginseng.

Fluorescent silicon nanoparticles (silicon dots) are low-toxicity nanomaterials of utmost interest to analytical and bioanalytical chemistry. Silicon dots have proved to be excellent fluorescent tags for sensor development applications. This review focuses on silicon dots and their fluorescent properties and applications. Silicon dots can be produced via nine basic synthetic methods and their fluorescent properties differ considerably, according to how they are produced and functionalized. The photoluminescent mechanism depends on the particle size, surface defects and functionalization molecules. This review presents a synopsis of the most important recent analytical and bioanalytical applications, along with the toxicity assays performed with silicon dots.

Dispersive liquid-liquid microextraction (DLLME) is a novel microextraction technique with a great potential in sample pretreatment, which has been increasingly used for preconcentration of diverse analytes. This review updates the state of the art and discusses promising prospects of DLLME, especially focuses on its combined use with chromatographic techniques for organic compounds analysis in environmental water samples. General and specific concepts of the fundamental theory of DLLME are described, and examples of recent innovations and applications are provided to demonstrate its potential for the determination of a wide range of organic compounds in various water matrices. Moreover, some limitations related to DLLME are also discussed in detail, and an outlook on the future of the technique, specifically its coupling with other pretreatment approaches, separation and detection techniques, is also given.

The carbapenems are a group of β-lactam antibiotics. The analogs of carbapenem (imipenem, panipenem, meropenem, ertapenem, biapenem and doripenem) used in treatment have an exceptionally broad spectrum of antibacterial activity. Several carbapenems are in advanced clinical trials (tebipenem, lenapenem, sulopenem, tomopenem). The aim of this review is to present the development and applicability of the analytical methods for the determination of carbapenems in biological fluids and pharmaceutical preparations. Carbapenems are easily degraded in aqueous solutions and in solid state. The kind of degradation products of carbapenems depends on several factors (solvents, pH, concentration of drug, temperature). Therefore this paper also provides a comparative review of stability-indicating analytical techniques: spectrophotometry (derivative spectrophotometry, first derivative with or without subtraction technique, first derivative of ratio spectra, biavariate analysis), chromatography (high-performance liquid chromatography - HPLC, coupled TLCdensitometry) and capillaryelectrophoresis (capillary zone electrophoresis - CZE and micellarelectrokinetic capillary chromatography - MEKC) for the determination of carbapenems in the presence of their degradation products.

A quick, reliable micellar electrokinetic chromatography (MEKC) method was developed and validated for the analysis of sitagliptin phosphate in tablets. Separation was carried out in fused silica capillary (48.0 cm total length and 40.0 cm effective length, 50 μm i.d.) by applying a potential of 30 kV (positive polarity), hydrodynamic injection by 50 mbar for 5 s and the temperature of the capillary cartridge was 25 °C. The selected electrolyte consisted of 50 mM TRIS (pH 10.6) to which 75 mM SDS was added (direct UV/PDA detection at 207 nm). The method was validated in terms of specificity, linearity, precision, accuracy and robustness. The method was linear (r = 0.9990) at a concentration range of 50.0 to 150.0 μg mL-1, precise (intra-day relative standard deviation [RSD] and inter-day RSD values < 2.0%), accurate (mean recovery = 101.0%), specific and robust. Moreover, the Plackett-Burman experimental design was used to evaluate robustness, producing results within the acceptable range. The photodegradation kinetics of the drug was evaluated and could be best described as second order kinetics (R2= 0.9838). This proposed method was successfully applied to the quality control analysis of sitagliptin, emphasizing thus the advantages of the method: high efficiency and resolution, rapid analysis and low consumption of sample and reagents.

In this study the effect of the presence of some different additives on non-aqueous capillary electrophoresis (NACE) separations of some structurally related compounds belonging to beta-blockers, antidepressants or neuroleptics were examined. Presence of surfactant was found to have a strong effect on separations. The anionic surfactant sodium dodecyl sulfate (SDS) enhanced separation of neuroleptics and beta-blockers. Upon combination between SDS and toctyl- calix[4]arene-tetra-ethylester (TOCXTEE) separation of beta-blockers could be optimized. Use of cyanomethylcalix [4]arene (CMCX[4]) with buffer including SDS for separation of neuroleptics elongated the separation time and had some positive and negative effects on separation. The cationic surfactant tetrabutylammonium-bromide (TBAB) was found to be better than that of SDS for the separation of antidepressants. Structure of analytes and calixarenes played an effective role in separation.

The electrochemical study of varenicline (VAR) was done in a wide pH range (2-12), at boron doped diamond electrode (BDDE), glassy carbon electrode (GCE) and hanging mercury electrode (HMDE), using cyclic (CV), square wave (SW) and adsorptive stripping square wave (AdSSW) voltammetric techniques. Depending on the pH and the type of the working electrode the characteristic electrochemical behavior of varenicline was established. The mechanism of the reduction process was suggested. Based on the obtained results, the new electroanalytical method was developed for its determination in the buffer solutions and plasma samples. By applying a square wave voltammetry (SWV) on BDDE and GCE, at pH 3.5 and 4.0, the linear dependence in plasma samples was achieved within the concentration range from 2×10-6 - 1×10-5 M and 4×10-6 - 1×10-5 M, respectively. Limit of detection (LOD) and limit of quantification (LOQ) were obtained as 7.1×10-7 M and 2.4×10-6 M on BDDE, and 1.0×10-6 M and 3.5×10-6 M on GCE, respectively. The recovery and RSD values obtained for VAR in plasma suggested BDDE electrode to be preferable in comparison with GCE. The accuracy of the voltammetric method was confirmed by the determination of VAR in plasma spiked with Champix® tablets and the results were statistically compared with those obtained with Ultra Performance Liquid Chromatography (UPLC) method, as a reference one.

Advanced oxidation process (AOP) is a widely used technique in environmental remediation of pollutants. Photocatalytic oxidation processes using iron system with H2O2 involve OH radical formation, which aids the degradation of pollutants in the aqueous system. Detection of hydroxyl radical is generally done in ESR spectrometry using DMPO as the spin trapping agent. Here, Methylene Blue (MB) was chosen as the test dye and three iron(III)-complexes, namely iron(III)-salen ferrioxalate, iron(III)-salen and iron(III)-acetylacetonate with H2O2, were chosen as photo-Fenton agents. All the systems were effective on the degradation of MB dye. However, the iron(III)-salen complex with H2O2 did not show its corresponding DMPO-OH signal in ESR. Hence, the present work was initiated to develop an alternative methodology for the determination of hydroxyl radicals in any remediation process (classical and non-classical photo- Fenton systems). Benzoic acid, here used as a chemical probe, gets hydroxylated to salicylic acid (SA) by the hydroxyl radicals, and the complex formed by SA with Fe3+ ions was measured spectroscopically. The formation of SA had increased with increase in the irradiation time, which indicates the progress of OH radicals. Interference study reveals that the detection of SA is unaffected in the presence of different electrolytes (c = 5 × 10-5 M). Repeatability of the developed method was verified, and it has significant precision (≤ 1.4% RSD, n = 5). Hence, this methodology could be used as a semi-quantitative tool for the determination of OH radicals in the environmental remediation by AOP.

A solid-phase extraction method using mixed hemimicelles and high-performance liquid chromatographydiode array detection was proposed for the pre-concentration and determination of anthraquinones (AQs) in Radix et Rhizoma Rhei samples. The mixed hemimicelles were synthesized by coating cetyltrimethylammonium bromide (CTAB) on Fe3O4 nanoparticles. Based on the superparamagnetic character of Fe3O4 nanoparticles, the proposed method had some special advantages, including high surface area, facile dispersion, rapid separation, convenient utilization, and environmental benignity. Some important factors that influence extraction efficiency of AQs, including amounts of Fe3O4 nanoparticles and CTAB, solution pH, extraction time, and desorption solvent, were optimized. Under optimum conditions, the recoveries of analyses done on samples spiked with the target analytes were between 96.7% and 106.6%; relative standard deviations ranged from 0.4% to 6.6%. The correlation coefficients varied from 0.9993 to 0.9998. The limits of detection ranged from 2.57 to 6.58 ng mL–1 (at a signal-to-noise ratio of 3). The method developed in the present work is feasible for sample pretreatment of herbal medicines.

A simple and sensitive isocratic reverse-phase high performance liquid chromatography method coupled with charged aerosol detection (HPLC-CAD) was developed and validated for the determination of gabapentin concentrations in a pharmaceutical formulation and in biological samples (rat serum and urine). Biological samples were simply treated with acetonitrile and directly injected into the HPLC without any further extraction or derivatization procedures. The separation was achieved on a GraceSmart RP-C18 packed column (250 × 4.6 mm, 5 μm) using a methanol-water (55:45, v/v) mobile phase at a flow rate of 1.1 mL/min at 30 °C. The total run time was less than 8 min. The standard calibration curves were linear (r2 > 0.998) over the range of 2-300 μg/mL for the pharmaceutical formulation, 25-800 μg/mL for rat serum and 50-1600 μg/mL for rat urine. The limits of detection (signal/noise = 3) were 0.5 μg/mL, 10 μg/mL and 15 μg/mL for pharmaceutical formulation, serum and urine, respectively. The intra-day and inter-day precisions in the pharmaceutical formulation analysis ranged between 2.7-3.9% and 3.1-4.4%, respectively. In the rat serum analysis, the intra-day and inter-day precision ranges were 3.5-4.7% and 3.0-9.0%, respectively, while the rat urine analysis intra-day and inter-day precision ranges were 1.9-7.6% and 4.2-9.9%, respectively. The developed HPLC-CAD method successfully determined gabapentin concentrations in commercial gabapentin tablets, as well as in rat serum and urine samples after drug administration.

For a set of 178 volatile organic compounds with highly diverse chemical structures, including terpenes, oxygenated terpenes such as esters, aldehydes, ketones, acids and alcohols, oxygenated benzene compounds, alkanes and so forth, the gas chromatographic programmed-temperature retention indices (PTRIs) have been modeled quantitatively using topological indices. A prediction model constructed by a recently proposed method named modeling based on subspace orthogonal projection (MSOP) with Monte-Carlo cross-validation (MCCV) was developed. The correlation coefficient R = 0.9993 and the root mean square error of prediction RMSEP=36.0 i.u. A prediction dataset including 20 compounds collected from the NIST web-book was further used to verify the stability and accuracy of the constructed model, a low root mean square error of prediction (RMSEP =32.6 i.u.) was obtained. Consequently, the developed prediction model can support the identification of natural volatile compounds more unambiguously by GC-MS when the retention data for candidate structures are not available.

Angiotensin-I converting enzyme (ACE) has an important function in blood pressure regulation. ACEinhibitory peptides can lower blood pressure by inhibiting ACE activity. In this investigation, water-soluble proteins were extracted from yeast (Saccharomyces cerevisiae) and hydrolyzed by yeast protein extraction enzyme to isolate ACEinhibitory peptides. Peptides with ACE-inhibitory activity were further separated and purified by ultrafiltration and fast protein liquid chromatography (FPLC). A hexapeptide, Thr-Pro-Thr-Gln-Gln-Ser, with a calculated molecular weight of 660Da, was purified and identified by MALDI-TOF-MS. The hexapeptide showed remarkable ACE-inhibitory activity, with an IC50 of 73.25 μg/mL. The level of ACE-inhibitory activity of the hexapeptide indicated that it is a good candidate for development of a hypotension drug or functional food.