Determination of inorganic phosphate by electroanalytical methods: A review

Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.     

Analytical Chemistry on the Femtoliter Scale

The compartmentalization of reactions in femtoliter (fL) containers and integration of fL containers into arrays not only enhances and accelerates chemical and biochemical analysis but also leads to new scientific methods and insights. This review introduces various fL container and array formats and explores their applications for the detection and characterization of biologically relevant analytes. By loading analytes, sensing elements, or cells into fL arrays, one can perform thousands of analytical measurements in parallel. Confining single enzyme molecules in fL arrays enables one to analyze large numbers of individual enzyme molecules simultaneously in solution. New nanofabrication techniques and progressively more sensitive detection methods drive the field of fL analytical chemistry. This review focuses on the progress and challenges in the field of fL analytical chemistry with examples of both basic and applied research.     

Engineered cells as biosensing systems in biomedical analysis

Over the past two decades there have been great advances in biotechnology, including use of nucleic acids, proteins, and whole cells to develop a variety of molecular analytical tools for diagnostic, screening, and pharmaceutical applications. Through manipulation of bacterial plasmids and genomes, bacterial whole-cell sensing systems have been engineered that can serve as novel methods for analyte detection and characterization, and as more efficient and cost-effective alternatives to traditional analytical techniques. Bacterial cell-based sensing systems are typically sensitive, specific and selective, rapid, easy to use, low-cost, and amenable to multiplexing, high-throughput, and miniaturization for incorporation into portable devices. This critical review is intended to provide an overview of available bacterial whole-cell sensing systems for assessment of a variety of clinically relevant analytes. Specifically, we examine whole-cell sensing systems for detection of bacterial quorum sensing molecules, organic and inorganic toxic compounds, and drugs, and for screening of antibacterial compounds for identification of their mechanisms of action. Methods used in the design and development of whole-cell sensing systems are also reviewed.     

Miniaturized sample preparation combined with liquid phase separations

Miniaturized sample preparation methods designed as the sample pretreatment for liquid phase separations, such as liquid chromatography, capillary electrophoresis and capillary electrochromatography, have been reviewed especially for the on-line coupling of the sample preparation process and the separation process. The development of the desorption interfaces for the effective combining of the sample preparation and subsequent liquid phase separations is briefly described along with the applications of the combined analytical systems to the analysis of complex sample mixtures such as biological and environmental matrices. Novel use of fine polymeric filaments as the extraction medium for microscale liquid phase separation methods are investigated and a comparison is made with other sample preparation techniques. Polymer coating onto the fibrous material is also introduced to further develop microscale sample preparation methods with improved extraction performance. Several other microscale sample preparation methods having a potential compatibility to the liquid phase separations are also described for future applications of these techniques.     

High resolution magic angle spinning NMR in combinatorial chemistry

Solid phase organic chemistry coupled with combinatorial methods promises to increase dramatically the diversity and number of small molecules available for medical and biological applications. However, optimizing the reaction conditions can be a time consuming step, especially since analytical tools to monitor reaction progress and detect impurities for solid phase chemistry are less developed than for solution chemistry. The use of high resolution magic angle spinning (HRMAS) NMR is described here as such an analytical tool. Whereas initial applications of molecular identification using deuterated organic solvents to swell the resins presented a significant gain in time over the cleave-and-analysis methods, the introduction of a differential diffusion filter has made immediate recording of spectra possible without any sample treatment. The applications of HRMAS NMR to different solid supports that are used in combinatorial chemistry will be described in terms of rapidity, robustness and sensitivity.     

Supramolecular optical sensor arrays for on-site analytical devices

Supramolecular optical chemosensors are useful tools in analytical chemistry for the visualization of molecular recognition information. One advantage is that they can be utilized for array systems to detect multiple analytes. However, chemosensor arrays have been evaluated mainly in the solution phase, which limits a wide range of practical applications. Thus, appropriate solid support materials such as polymer gels and papers are required to broaden the scope of the application of chemosensors as on-site analytical tools. In this review, we summarize the actual approaches for the fabrication of solid-state chemosensor arrays combined with powerful data processing techniques and portable digital recorders for real-world applications.     

A review on the fabrication of substrates for surface enhanced Raman spectroscopy and their applications in analytical chemistry

This work reviews different types of substrates used for surface-enhanced Raman scattering (SERS) that have been developed in the last 10 years. The different techniques of self-assembly to immobilize metallic nanoparticles on solid support are covered. An overview of SERS platforms developed using nanolithography methods, including electron-beam (e-beam) lithography and focused ion beam (FIB) milling are also included, together with several examples of template-based methodologies to generate metallic nano-patterns. The potential of SERS to impact several aspects of analytical chemistry is demonstrated by selected examples of applications in electrochemistry, biosensing, environmental analysis, and remote sensing. This review shows that highly enhancing SERS substrates with a high degree of reliability and reproducibility can now be fabricated at relative low cost, indicating that SERS may finally realize its full potential as a very sensitive tool for routine analytical applications.     

Hydrodynamic modulation voltammetry

Highly efficient background-correction techniques applicable to voltammetric methods of trace analysis can be developed by modulating the convection rate of the solution at a solid electrode surface. The theoretical aspects, advantages, disadvantages, and analytical applications of the various batch and flow approaches to hydrodynamic modulation voltammetry are discussed, together with trends in future developments.     

微孔有机聚合物在样品前处理技术中应用的研究进展

微孔有机聚合物（microporous organic polymers,MOPs）是一类由轻元素组成的新型多孔材料,具有骨架密度低、比表面积大、孔尺寸可调控、表面可修饰、化学和物理性质稳定等优点。近年来,MOPs在样品前处理领域展现出巨大的应用潜力。本文综述了MOPs的结构类型及合成方法,以及MOPs在固相萃取、批处理吸附萃取、整体柱和传感膜等样品前处理技术中的应用。     

Extraction and stirring integrated techniques: examples and recent advances

Extraction techniques, which focus on selectivity and sensitivity enhancement by isolation and preconcentration of target analytes, are essential in many analytical methods. Because many extraction techniques occur under diffusion-controlled conditions, stirring of the sample solution is required to accelerate the extraction by favoring diffusion of the analytes from the bulk solution to the extractant phase. This stirring may be performed by use of an external device or by integrating extraction and stirring in the same device. This review focuses on the latter techniques, which are promising methods for sample treatment. First, stir-bar-sorptive extraction, the most widely used method, is considered, paying special attention to the development of new coatings. Finally, a general overview of novel integrated techniques in both solid-phase and liquid-phase microextraction is presented; their main characteristics and marked trends are reported.     

Microextraction sample preparation techniques in forensic analytical toxicology

Sample preparation is a critical step in forensic analytical toxicology. Different extraction techniques are employed with the goals of removing interferences from the biological samples, such as blood, tissues and hair, reducing matrix effects and concentrating the target analytes, among others. With the objective of developing faster and more ecological procedures, microextraction techniques have been expanding their applications in the recent years. This article reviews various microextraction methods, which include solid‐based microextraction, such as solid‐phase microextraction, microextraction by packed sorbent and stir‐bar sorptive extraction, and liquid‐based microextraction, such as single drop/hollow fiber‐based liquid‐phase microextraction and dispersive liquid–liquid microextraction, as well as their applications to forensic toxicology analysis. The development trend in future microextraction sample preparation is discussed.     

Studies of the interface of conducting polymers with inorganic surfaces

Many of the properties of multi-material systems and relevant devices depend on the interfaces between the different components. This review focuses on characterization of the interfaces between intrinsically conducting polymers and inorganic materials consisting of metals and metal oxides. These materials are chosen because of their importance in several analytical applications. Although use of conducting polymers and metals or metal oxides in analytical systems, specifically in sensing, is well established, the number of novel materials used for analytical purposes is continuously increasing. This further increases the possible number of effective combinations of different materials within multicomponent systems. As a consequence, innovative characterization techniques have become as important as more conventional techniques. On the other hand, sophisticated characterisation techniques are increasingly widespread and, consequently, also readily accessible. This critical review is not an exhaustive discussion of all possible analytical techniques suitable for characterization of interfaces. It is, instead, limited to an overview of the most effective, relatively widespread techniques, emphasising their most significant recent advances. Critical analysis of the individual techniques is complemented by a few selected examples.     

A fluorescent anion sensor that works in neutral aqueous solution for bioanalytical application

Anion recognition and anion sensing are of interest because anions play many important roles in living organisms. Most currently known anion sensors work only in organic solution, but sensors for biological applications are required to function in neutral aqueous solution. We have designed and synthesized a novel fluorescent sensor for anions. The sensor molecule 1-Cd(II) contains 7-amino-4-trifluoromethylcoumarin as a fluorescent reporter and Cd(II)-cyclen (1,4,7,10-tetraazacyclododecane) as an anion host. In neutral aqueous solution, Cd(II) of 1-Cd(II) is coordinated by the four nitrogen atoms of cyclen and the aromatic amino group of coumarin. When various anions are added to 100 mM HEPES buffer solution (pH 7.4) containing 1-Cd(II), the aromatic amino group of coumarin is displaced from Cd(II), causing a change of the excitation spectrum. While pyrophosphate and citrate were detected with high sensitivity, fluoride and perchlorate produced no response. Among organic anions, ATP and ADP gave strong signals, while cAMP showed little signal. By utilizing the different affinities of the sensor for AMP and cAMP, the activity of phosphodiesterase, which cleaves cyclic nucleotide, was monitored in real-time. The sensor should have many biochemical and analytical applications and the sensing principle should be widely applicable to the sensing of other molecules.     

Current status of modern analytical luminescence methods

Modern analytical luminescence methods and their recent applications are reviewed with emphasis on the most sensitive methods that can be expected to be useful in future microanalytical systems such as μ-TAS, lab-on-chip, point-of-care (POC) and high throughput screening (HTS) applications. Photoluminescence (PL) is presently the most important group of analytical techniques utilising luminescence. Because of the rapidly increasing popularity of electrochemiluminescence (ECL) and its applications, we have given particular attention to ECL mechanisms and techniques. Due to the present and future importance of capillary electrophoresis (CE) as a separation method, the CE detection methods based on luminescence are also considered in a relatively detailed way. For those researchers, designing novel experiments and assays, experimental set-ups, and apparatus we include web links to the manufacturers of some fairly rare reagents, as well as modern instrument components.     

High resolution magic angle spinning NMR for analyzing small molecules attached to solid support

Solid phase synthesis has become a routine technique in combinatorial chemistry. The need in analytical methods to characterize nondestructively resin bound molecules has been fulfilled by the introduction of High Resolution Magic Angle Spinning (HR MAS) NMR of solvent swollen beads. HR MAS NMR can give solution like proton NMR spectra and one- and two-dimensional NMR techniques are amenable, allowing detailed structure analysis. Recent developments are the application of a diffusion filter to suppress solvent signals and dipolar recoupling techniques to gain spatial information. HR MAS NMR has been applied to monitor reactions and elucidate reaction products.     

Comparison of ion chromatography and capillary electrophoresis for the determination of inorganic ions

The techniques of ion chromatography and capillary electrophoresis are compared as analytical methods for the determination of inorganic anions and cations. Comparison is made in the areas of stage of development, separation efficiency, separation selectivity, analytical performance parameters, method development procedures, applications, strenghts and weaknesses, and future directions. It is shown that the two techniques are complementary rather than competitive, especially with regard to their separation selectivities and the type of applications to which they are most suited.     

Biomolecules as promising ligands in the synthesis of metal nanoclusters: Sensing,bioimaging and catalytic applications

The use of metal nanoclusters as sensing probes has recently attracted considerable interest from researchers. In particular, metallic nanoclusters (e.g., Au, Ag, Cu, Pt) have been noticed a wide range of applications in the field of fluorescence sensing and bioimaging. The stabilization of metal nanoclusters with organic molecules, proteins, and amino acids enhances their optical properties and analytical applications. In this review, synthetic routes for the fabrication of metal nanoclusters are summarized. This review also describes the metal nanoclusters properties including aggregation-induced emission, optical absorption, non-linear optical, and chiral properties. We discussed the analytical applications of metal nanoclusters for sensing of wide variety of analytes including drugs, biomolecules, biomarkers. Further, the catalytic applications of metal nanoclusters are also briefly summarized. Finally, we summarize the challenges and future perspectives of metal nanoclusters in analytical chemistry.     

Classification and Principles of Planar Chromatography in Test Methods of Chemical Analysis

The test methods of chemical analysis with the use of various versions of planar chromatography are considered. Cellulose paper and thin silica gel layers on polymer supports are used as stationary-phase carriers. The test solution serves as a mobile phase. The length of a colored or decolorized zone in test strips (laminated in a transparent polymer film) obtained by contact with the test solution through a small orifice or slot in the film serves as an analytical signal. Planar chromatography in the test methods of chemical analysis is classified in accordance with the mechanism of interactions between the mobile and stationary phases: precipitation, acid-base (proton-exchange), chemisorption, complexation, redox (electron-exchange), catalytic, and adsorption chromatography. Examples of stationary phases and particular analytical applications are given.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 8, 2005, pp. 869–876.Original Russian Text Copyright © 2005 by Amelin.     

Piezoelectric transmission spectroelectrochemistry with a normal piezoelectric quartz crystal as an optically-transparent electrode

Piezoelectric transmission spectroelectrochemistry (PTSEC), i.e., the combination of electrochemistry and spectroelectrochemistry (SEC) with electrochemical quartz crystal microbalance (EQCM) technique is reported by using a normal piezoelectric quartz crystal (PQC) as an optically-transparent electrode (OTE). A theoretical relationship between the PQC response and the spectroelectrochemical response is derived and used to estimate the apparent molar absorptivity of the absorbing species deposited on the OTE on the PQC surface. The complex of copper with aspartic acid is used to test this new PQC-SEC technique. Results show that the combination of three such diverse techniques provides a very useful methodology for studying electrode processes and electrode surface characteristics in situ.     

In Situ Monitoring of Generation and Precipitation of Ferric Hydroxide Sol with a Piezoelectric Quartz Crystal Impedance Analyzer

The piezoelectric quartz crystal (PQC) impedance technique was applied to monitor in situ generation and precipitation of the ferric hydroxide sol in aqueous solutions at 90 degrees C. Equivalent circuit parameters and resonant frequencies as well as the half-peak width of the electroacoustic conductance spectrum deltaf(G1/2) for the PQC resonance were obtained and analyzed. Three stages, sol generation and simultaneous adsorption, adsorption equilibrium, and precipitation of ferric hydroxide sol could be identified in the process of adding the ferric nitrate solution into the hot water. A scheme of two consecutive reactions occurring at the electrode/solution interface was used to analyze the adsorption kinetics of ferric hydroxide sol onto the Au electrode. In addition, the electrolyte-induced precipitation of the colloid was monitored and discussed. Temperature effect on the PQC resonance behavior in liquid was also investigated. Since the PQC impedance technique provides multidimensional piezoelectric information in situ, it is highly recommended for studying the process of sol-gel generation and precipitation. Copyright 2001 Academic Press.