Recent advances in applications of single-drop microextraction: a review

During the past fifteen years since its introduction, single-drop microextraction has witnessed incessant growth in the range of applications of samples preparation for trace organic and inorganic analysis. This was mainly due to the array of modes that are available to accomplish extraction in harmony with the nature of analytes, and to use the extract directly for analysis by diverse instrumental methods. Whilst engineering of novel sorbent materials has expanded the sample capabilities of rival method of solid-phase microextraction, the single-drop microextraction – irrespective of the mode of extraction – uses common equipment found in analytical laboratories sans any modification, and in a much economic way. The recent innovations made in the field, as highlighted in this review article in the backdrop of historical developments, are due to the freedom in operational conditions and practicability to exploit chemical principals for optimum extraction and sensitive determination of analytes. Literature published till July 2011 has been covered.     

Cyclic voltammetry of highly hydrophilic ions at a supported liquid membrane

Cyclic voltammetry has been used to study the coupling of ion transfer reactions at a liquid membrane. The liquids are either supported by a porous hydrophobic membrane (polyvinylidene difluoride, PVDF) when the organic solvent is non-volatile (o-nitrophenyloctylether) or are merely a free standing organic solvent layer such as 1,2-dichloroethane comprised between two hydrophilic dialysis membranes supporting the adjacent aqueous phases. The passage of current across the liquid membrane is associated with two ion transfer reactions across the two polarised liquid liquid interfaces in series. It is shown that it is possible to study the transfer of highly hydrophilic ions at one interface by limiting the mass transfer of the other ion transfer reaction at the other interface. Indeed, for systems comprising an ion M in one aqueous phase and a reference ion R partitioned between the membrane and the other aqueous phase, the observed and simulated cyclic voltammograms have a half-wave potential determined by the Gibbs energy of transfer of M transferring at one interface and by the limiting mass transfer of R at the other interface. This new methodology opens a way to measure the Gibbs energy of transfer of highly hydrophilic or hydrophobic ions, which usually limits the potential window at single liquid liquid interfaces (ITIES).     

Smart and green interfaces: From single bubbles/drops to industrial environmental and biomedical applications

Interfaces can be called Smart and Green (S&G) when tailored such that the required technologies can be implemented with high efficiency, adaptability and selectivity. At the same time they also have to be eco-friendly, i.e. products must be biodegradable, reusable or simply more durable. Bubble and drop interfaces are in many of these smart technologies the fundamental entities and help develop smart products of the everyday life.     

Determination of As(III) by anodic stripping voltammetry using a lateral gold electrode: experimental conditions, electron transfer and monitoring of electrode surface

The aim of this work is to evaluate the efficiency of the determination of As(III) by anodic stripping voltammetry (ASV) using a lateral gold electrode and to study the modifications of the electrode surface during use. Potential waveforms (differential pulse and square wave), potential scan parameters, deposition time, deposition potential and surface cleaning procedure were examined for they effect on arsenic peak intensity and shape. The best responses were obtained with differential pulse potential wave form and diluted 0.25 M HCl as supporting electrolyte. The repeatability, linearity, accuracy and detection limit of the procedure and the interferences of cations and anions in solution were evaluated. The applicability of the procedure for As(III) determination in drinking waters was tested. Cyclic voltammetry (CV) was used to study the electrochemical behaviour of As(III) and for the daily monitoring of electrode surface. Also scanning electron microscopy (SEM) analysis was used to control the electron surface. Finally we evaluated the possibility to apply the equations valid for flow systems also to a stirred system, in order to calculate the number of electrons transferred per molecule during the stripping step.     

Hydrodynamic voltammetry at the liquid|liquid interface: facilitated ion transfer and the rotating diffusion cell

A new approach to the voltammetric investigation of facilitated ion transfer processes is reported. The technique uses a rotating diffusion cell approach to induce laminar flow in the organic phase of a liquid|liquid electrochemical cell. The interface between two immiscible electrolyte solutions (ITIES) was stabilised against rotation with either γ-alumina or a track-etched polyester membrane. The resultant voltammetry is shown to be consistent with the Koutecký–Levich equation enabling kinetic parameters associated with facilitated transfer of sodium by dibenzo-18-crown-6 across the water|1,2-dichloroethane interface to be evaluated. In particular, the use of the more hydrophilic alumina membrane permits the uncertainties regarding the use of the membrane-stabilised ITIES, namely the interfacial position, to be eliminated.     

Responsive polymers for analytical applications: A review

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations. From this review, we hope to make clear that while the history of using stimuli-responsive polymers for analytical applications is rich, there are still a number of directions to explore and exciting advancements to be made in this flourishing field of research.     

薄层循环伏安法研究硝基苯/水界面上离子诱导的电子转移反应

应用薄层循环伏安法研究了硝基苯/水两相界面间,且有共同离子四丁基铵TBA+存在于两相中,在有机相中的四氰化二甲基苯醌(TCNQ)与水相中的K4Fe(CN)6之间发生的反向电子转移反应。在直径为0.64cm的裂解石墨电极上用2μL硝基苯溶液使之自然扩散在电极表面形成薄层的有机相,并以此作为工作电极。对电极为铂丝(0.5mm),参比电极为Ag/AgCl电极,均置于总体积为2mL的水相中。由于共同离子TBA+的诱导,在硝基苯/水界面间,在已氧化的TCNQ+阳离子(在有机相中)与[Fe(CN)6]4-阴离子(在水相中)之间发生了反向电子转移反应。试验证明:在一定条件下,通过改变两相中共同离子的浓度,可使一些不能发生的两相界面的电子转移反应得以发生;这类电子转移反应系受界面电位差所控制。此外,还测得了在恒定的共同离子浓度比值的条件下,此两相界面电子转移反应的表观速率常数(k)为0.135cm.s-1.mol-1。     

Stripping voltammetry at micro-interface arrays: A review

In this article, a comprehensive overview of the most recent developments in the field of stripping voltammetry at regular micro-interfaces (both solid–liquid and liquid–liquid interfaces) is presented. This review will report on the most conventional arrays of metallic micro-electrodes but also on the rapidly growing field of electrochemistry at arrays of micro-interfaces between two immiscible electrolyte solutions (μITIES). The main fabrication methods, together with some design considerations and diffusion phenomena at such interfaces are discussed. Main applications of micro-interface arrays are presented including heavy metals detection at micro-electrode arrays and detection of organic molecules (amino acids, vitamins, peptides and drugs) at the μITIES. Stripping analysis at micro-interface arrays is suitable for the detection of analytes in several real media including water, soil extracts and biological fluids (blood and saliva) with high specificity, sensitivity (detection limits of nM, ppb level) and reliability. Stripping analysis at μITIES and micro-electrode arrays are two complementary approaches that have the advantages of being cost effective, simple to use and easily adaptable to field measurement.     

Molecular modeling and photovoltaic applications of porphyrin-based dyes: A review

In this review, the introduction of solar cells is presented. Old and new generation solar cells are briefly described. Quantum dot solar cells (QDSCs), perovskite solar cells, and dye-sensitized solar cells (DSSCs) are concisely introduced. The sensitization mechanism in DSSCs is discussed in detail concerning the spectral and electron injection properties of different dyes. An analysis of the intramolecular charge transfer process in the excited dye molecule is also provided. The use of porphyrin-based dyes as sensitizers in DSSCs is then reviewed. The design, synthesis, and photovoltaic application of a wide variety of porphyrin-based dyes as well as porphyrin dyads are presented and discussed. Theoretical studies of the spectral and electronic properties of different porphyrin-based dyes using DFT and TD-DFT methods are described. The different possibilities for improving the light-to-electrical energy conversion performance are discussed, such as structural modifications through introducing push-pull moieties, which in turn tunes the HOMO-LUMO energy gap of the sensitizing dye used in the DSSC. Experimental, as well as theoretical calculations of adsorption energies of the sensitizing dyes, are crucial for predicting the relative performance and efficiency of the dyes.     

应用扫描电化学显微镜研究极化液/液界面上的电子转移反应

将含有氧化还原电对的水溶液滴涂在铂盘电极表面, 然后将该电极插入到1,2-二氯乙烷溶液中, 形成稳定的油/水界面. 液滴中的K3Fe(CN)6和K4Fe(CN)6氧化还原电对既可以作为水相中的参比电对参与控制液/液界面上的电势差, 同时又可以作为水相的电子授受体参与界面上的电子转移反应. 结合扫描电化学显微镜电化学系统的特点, 利用其双恒电位仪分别控制界面电势差和现场扫描的优点, 通过扫描电化学显微镜的渐进曲线得到了不同界面电势差控制的电子转移反应速率常数. 实验结果表明, 应用此方法获得的液/液界面可以被外加电位极化, 在一定的电势差范围内, 反应速率常数与界面电势差的关系遵守Butler-Volmer公式.     

Electrochemical oxidation of cisatracurium on carbon paste electrode and its analytical applications

The electrochemical oxidation of cisatracurium was investigated by cyclic voltammetry and differential pulse voltammetry at a carbon paste electrode and the experimental parameters have been optimized in order to obtain the optimum analytical signal. A differential pulse voltammetric method with carbon paste electrode is described for the determination of cisatracurium with detection limit of 0.38 μg/ml and quantitation limit of 1.26 μg/ml. The proposed method was applied to determine the content of cisatracurium in human urine and human serum, obtaining accurate and precise results.     

New materials: analytical and environmental applications in ion chromatography

This review details ion chromatography developments and related applications, mainly in the field of environmental analysis, gained by the evolution in the science and technology for new stationary phases. Unconventional approaches to ion chromatographic separations are also outlined.     

A Fullerene/Lipid Electrode Device: Reversible Electron Transfer Reaction of C60 Embedded in a Cast Film of an Artificial Ammonium Lipid on an Electrode in Aqueous Solution

Two reversible one-electron transfers are observed for an electrode device made from C₆₀ and an artificial lipid (see schematic drawing). Cyclic voltammetric studies reveal that the redox couples are unchanged even after 50 cycles, thus indicating that the C₆₀ radical monoanion and the C₆₀ dianion generated in aqueous solution are very stable.     

SOAS: A free program to analyze electrochemical data and other one-dimensional signals

This paper describes an open source program called SOAS, which we developed with the aim of analysing one-dimensional signals. It offers a large set of commands for handling voltammetric and chronoamperometric data, including smoothing signals, differentiation, subtracting baselines, fitting current responses, measuring limiting currents, and searching for peak positions. Although emphasis is on the analysis of electrochemical signals, particularly protein film voltammetry data, SOAS may also prove useful for processing spectra. This free program is available by download from the Internet, and can be installed on computers running any flavor of Unix or Linux, most easily on MacOS X.     

A thermodynamic study on the complexation between riboflavin and a diaminotriazine derivative mediated by triple hydrogen bonds at water/oil interfaces

The changes in Gibbs free energy (ΔG _int), enthalpy (ΔH _int) and entropy (TΔS _int) upon complexation between riboflavin (RF) and N,N-dioctadecyl-[1,3,5]triazine-2,4,6-triamine (DTT), mediated by triple hydrogen bonds at water/carbon tetrachloride, trichloroethylene and chloroform interfaces, were determined via temperature-controlled interfacial tension measurements. It was shown that hydrogen bonding interactions between RF and DTT were best characterized by large and negative ΔH _int values, unlike those predicted from either the polarity in each phase or the arithmetic average of the polarities in the two phases. Furthermore, the ΔH _int values became more positive as the dielectric constant of the oil phase was increased. These results strongly indicate that ΔH _int is governed by the dielectric properties of the oil phase. Adsorption of RF, DTT and the RF-DTT complex at the water/oil interface gave rise to restrictions on the translational and rotational motions of these species, as demonstrated by the ΔS _int values observed, which is another characteristic of interfacial complexation. The thermodynamic parameters evaluated in the present study revealed the characteristic complexation behavior that occurs at a water/oil interface, as mediated by hydrogen bonding.     

Ion chromatography coupled with fluorescence/UV detector: A comprehensive review of its applications in pesticides and pharmaceutical drug analysis

Ion chromatography (IC) is a well-known technique for trace determination of inorganic ions and small organic acids. Recently, it has also appeared as a promising alternative to reverse phase chromatography for the determination of polar pesticides and pharmaceutical drugs in various sample matrices. Therefore, this study aims to provide a comprehensive overview of the application of IC coupled to fluorescence (FLD) or UV detector for the determination of pesticides and pharmaceutical drugs in samples from all walks of life. Apart from advantages and limitations, a short comparison of IC-FLD/UV with other techniques especially reverse-phase chromatography was drawn to envision future research efforts in this direction. Finally, several related areas such as IC hyphenation with different detectors (spectroscopic and spectrometer), miniaturization, automation, green chemistry, mobile phase, column, sample preparation, etc., were discussed to highlight its application for the determination of a wide range of analytes in the complex sample matrix.     

Membrane-based microextraction techniques in analytical chemistry: A review

The use of membrane-based sample preparation techniques in analytical chemistry has gained growing attention from the scientific community since the development of miniaturized sample preparation procedures in the 1990s. The use of membranes makes the microextraction procedures more stable, allowing the determination of analytes in complex and “dirty” samples. This review describes some characteristics of classical membrane-based microextraction techniques (membrane-protected solid-phase microextraction, hollow-fiber liquid-phase microextraction and hollow-fiber renewal liquid membrane) as well as some alternative configurations (thin film and electromembrane extraction) used successfully for the determination of different analytes in a large variety of matrices, some critical points regarding each technique are highlighted.     

Electrochemistry Inside Microdroplets of Kerosene: Electroanalysis of (Methylcyclopentadienyl) Manganese(I) Tricarbonyl(I)

A novel electrochemical technique for the determination of (methycyclopentadienyl) manganese(I) tricarbonyl in kerosene is presented. The protocol involves creating an ensemble of microdroplets via spraying a fine mist of the sample under investigation onto an electrode substrate which is then immersed into an immiscible supported phase of either water or acetonitrile which can be used to voltammetrically interrogate the species of interest. In particular the kerosene|acetonitrile interface allows the study of the electrochemical oxidation of (methycyclopentadienyl) manganese(I) tricarbonyl, MMT which normally occurs at large overpotentials (E_1/2=+1.22 V vs. saturated calomel electrode).     

Mesoporous platinum hosts for electrodeliquidliquid – Triple phase boundary redox systems

Mesoporous metal hosts are attractive electrode materials for complex electrode reactions, for example those involving a system of two immiscible liquids. Here we show that a solution of tetraphenylporphyrianto manganese (MnTPP) in 4-(3-phenylpropyl)-pyridine (PPP) organic liquid can be immobilized into mesoporous platinum thin films electrodeposited from a liquid crystalline template. When immersed in an aqueous solution, the organic liquid remains immobilized inside the mesoporous platinum framework. Well-defined, stable, and reproducible ion transfer voltammograms are recorded. The effects of mesoporous platinum membrane thickness (volume), scan rate, and the type of aqueous electrolyte anion (for Cl⁻, , , CN⁻, SCN⁻ and ) are investigated. Mesoporous platinum is proposed as a very effective electrode material for liquidliquid anion sensing and for other applications of electrochemically driven liquidliquid redox systems.