Showing papers in "Trends in Analytical Chemistry in 2010"

Graphene for electrochemical sensing and biosensing

Abstract: Graphene has proved to be an excellent nanomaterial for applications in electrochemistry. We review progress in constructing high-performance electrochemical sensors and biosensors. We also discuss: different routes for graphene fabrication; graphene-modified electrodes and graphene-composite electrodes for sensing, including those based on ionic liquids; incorporation of biorecognition elements into graphene-based electrodes; and, graphene-supported electrocatalytic nanoparticle-based electrochemical sensors and biosensors.

Liquid-phase microextraction

Abstract: The development of faster, simpler, inexpensive and more environmentally-friendly sample-preparation techniques is an important issue in chemical analysis. Recent research trends involve miniaturization of the traditional liquid-liquid-extraction principle by greatly reducing the acceptor-to-donor ratio. The current trend is towards simplification and miniaturization of sample preparation and decreasing the quantities of organic solvents used. We discuss liquid-phase microextraction with the focus on extraction principles, historical development and performance.

Critical review of chemometric indicators commonly used for assessing the quality of the prediction of soil attributes by NIR spectroscopy

Abstract: Near-infrared (NIR) and mid-IR spectroscopy applied to soil compositional analysis started to develop markedly in the 1990s, taking advantage of earlier advances in instrumentation and chemometrics for agricultural products. Today, NIR spectroscopy is envisioned as replacing laboratory analysis in certain applications (e.g., soil-carbon-credit assessment at the farm level). However, accuracy is still unsatisfactory compared with standard laboratory procedures, leading some authors to think that such a challenge will never be met. This article investigates the critical points to be aware of when accuracy of NIR-based measurements is assessed. First is the decomposition of the standard error of prediction into components of bias and variance, only the latter being reducible by averaging. This decomposition is not used routinely in the soil-science literature. Contrarily, a log-normal distribution of reference values is very often encountered with soil samples [e.g., elemental concentrations (e.g., carbon)] with numerous small or zero values. These very skewed distributions make us take precautions when using inverse regression methods (e.g., principal component regression or partial least squares), which force the predictions towards the centre of the calibration set, leading to negative effects on the standard error prediction – and therefore on prediction accuracy – especially when log-normal distributions are encountered. Such distributions, which are very common for soil components, also make the ratio of performance to deviation a useless, even hazardous, tool, leading to erroneous conclusions. We propose a new index based on the quartiles of the empirical distribution – ratio of performance to inter-quartile distance – to overcome this problem.

Fast screening methods to detect antibiotic residues in food samples

Abstract: Antibiotic residues in edible animal products are of great concern to regulatory agencies and consumers, so reliable screening methods for rapid, selective and sensitive detection of these residues are necessary to ensure food safety. In recent years, great efforts have been made to simplify the treatment of solid food samples and also to introduce high-throughput methods, so different screening methods have been developed. This review presents a general overview on the progress of the three most important screening approaches to detect antibiotic residues in food samples (i.e. immunoassays, microbiological tests and biosensors). Their main advantages are short analysis time, high sensitivity and selectivity for immunoassays, simplicity and low cost for microbiological tests, and automation and the possibility of in situ analysis for biosensors. Moreover, it is important to note a great increase in the number of commercial kits. Regarding the detection mode employed, the lowest limits of detection were achieved using microbiological inhibition tests and immunoassays with time-resolved fluorometry detection, so antibiotic residues at levels lower than the maximum residue limits established by legislation were detected.

Molecularly-imprinted polymers: useful sorbents for selective extractions

Abstract: We review and discuss the most common protocols for synthesizing molecularly-imprinted polymers (MIPs), highlighting their main advantages and drawbacks. We then evaluate the most recent applications of MIPs and focus on the strategies adopted most to overcome the drawbacks commonly encountered when applying MIPs in different matrices. We also highlight the different advantages that MIPs offer when they are used as sorbents in solid-phase extraction (SPE) to perform highly selective extractions, and the advantages that these sorbents have over the most commonly-used SPE sorbents by reviewing some of the latest studies reported in the literature.

Electrochemical sensing based on carbon nanotubes

Abstract: The singular chemical structure and the size of carbon nanotubes (CNTs) provide their extraordinary properties. Many researchers have used the electronic characteristics of CNTs to develop electrochemical analytical methods and sensing devices with improved characteristics. In this overview, we discuss the most significant innovations in electrochemical sensing based on CNTs, as reported in the past five years. We highlight the advantages of this type of nanostructured material and the main performance parameters achieved. We also discuss several problems that hinder the widespread use of these devices in practical applications and describe some possible future trends.

Greening analytical chromatography

Abstract: We review recent approaches for greening analytical separation technologies. Whereas conventional analytical separation technologies produce as much as 50 mL of waste per analysis, greener options considerably reduce the amount of waste generated per analysis, ranging from simply adoptable small-particle stationary-phase technologies and reduced column diameters to more specialized technologies [e.g., ultra-high-pressure liquid chromatography (UHPLC), supercritical-fluid chromatography (SFC) and microscale or nanoscale HPLC]. In addition, greener eluents and chromatography conditions can also be used, including substitution of ethanol for acetonitrile in reversed-phase HPLC and the use of water alone as an eluent at elevated temperatures. We describe the merits of these emerging technologies, and discuss the factors influencing the decision to move from conventional analytical separation methodologies to greener alternatives.

Dispersive liquid-liquid microextraction for determination of organic analytes

Abstract: One of the most important objectives of modern analytical chemistry is miniaturization, simplification and automation of the whole analytical procedure, especially to speed up sample treatment, which is currently the bottleneck of analysis. Introduction of dispersive liquid-liquid microextraction (DLLME) has greatly contributed to meeting this objective, due to its simplicity, rapidity of operation and low consumption of solvents and reagents. DLLME has attracted much interest from scientists working in separation science. Since its introduction in 2006 for preconcentration of organic analytes from water samples, a good number of works have reported efficient, quick extraction of organic or inorganic analytes. However, before using DLLME, there is a need to optimize carefully influential factors (e.g., types and volumes of extraction and disperser solvents, extraction time, sample amount, pH, and salt addition). The present review focuses on applications of DLLME for extracting organic analytes (e.g., pesticides, pharmaceuticals, polychlorinated biphenyls, and polybrominated diphenyl ethers) from the time that DLLME was introduced to the end of December 2009. We pay special attention to those works that represent an improvement in the technique and the most challenging applications.

Sum of ranking differences compares methods or models fairly

Abstract: This review covers a novel approach to comparing methods, based on the sum of ranking differences (SRD) Many method-comparison studies suffer from ambiguity or from comparisons not being quite fair This problem can be avoided if there are differences between ideal and actual rankings The absolute values of differences for the ideal and actual ranking are summed up and the procedure is repeated for each (actual) method The SRD values obtained such a way order the methods simply If the ideal ranking is not known, it can be replaced by the average (maximum or minimum of all methods or by a known sequence) SRD corresponds to the principle of parsimony and provides an easy tool to evaluate the methods: the smaller the sum the better the method Models and other items can be similarly ranked Validation can be carried out using simulated random numbers for comparison: an empirical histogram (bootstrap-like) shows whether the SRD values are far from random Two case studies (clustering of HPLC columns and prediction of retention data) illustrate and validate the applicability of this novel approach to comparing methods The technique is entirely general; it can be used in different fields (eg, for stationary-phase (column) selection in chromatography, model and descriptor selection, comparing analytical and chemometric techniques, determination of panel consistency, etc) The only prerequisite is that the data can be arranged in matrix form without empty cells

Review of analytical figures of merit of sensors and biosensors in clinical applications

Abstract: Although the development of clinical sensors and biosensors has increased in recent years, improvements in sensitivity, selectivity, limits of detection, fast response and miniaturization are yet to be attained Health care appears to provide the best opportunity for sensor development Among the wide range of different sensors and biosensors, electrochemical biosensors are the most common in the clinical field, due to their high sensitivity and selectivity, portability, rapid response time and low cost This article provides an up-to-date overview of the analytical performance of sensors and biosensors in clinical applications by discussing recent improvements, particularly due to the impact of nanotechnology

Vibrational spectroscopy provides a green tool for multi-component analysis

Abstract: Based on the literature published in the past decade, we focus on the possibilities offered by vibrational-spectroscopy-based techniques to make multi-component analysis of samples independently of their physical state. We discuss the main chemometric tools proposed for developing calibration models and solving problems derived from spectroscopic non-idealities (e.g., highly overlapped spectral bands or the presence of spectral non-linearity), and the benefits provided by vibrational-spectroscopy-based multi-component analysis in industry. Our main objective is to show that vibrational spectroscopy provides fast analytical methods that enable non-destructive analysis and permits, in a green way, the simultaneous analysis of multiple components from the same sample in a single instrumental measurement without environmental side effects.

An analytical overview of processes for removing organic dyes from wastewater effluents

Abstract: Organic dyes are used in a wide range of industrial applications (e.g., textiles, food products, cosmetics and pharmaceuticals), so they are frequently found in wastewaters and are increasingly becoming an environmental problem. This critical overview covers the most frequently used strategies for dye removal and the most common analytical techniques for monitoring these processes and identifying any intermediates generated. We also analyze experimental design strategies for optimizing removal processes. Finally, our concluding remarks include a future outlook for dye-removal processes and the analytical techniques employed.

Application of chemometrics to analysis of soil pollutants

Abstract: This overview focuses on the application of chemometrics techniques to the investigation of soils contaminated by polycyclic aromatic hydrocarbons (PAHs) and metals, because these two important and very diverse groups of pollutants are ubiquitous in soils. We highlight the salient features of studies carried out in the microenvironments and recreational environments of humans in the context of the multivariate statistical techniques available across the boundaries of disciplines used in soil studies. We pay particular attention to techniques employed in the geosciences that may be effectively utilized for environmental soil studies. We also discuss classical multivariate approaches that may be used in isolation or as complementary methods to these. Chemometrics techniques widely applied in atmospheric studies for identifying sources of pollutants or for determining the importance of contributions of contaminant sources to a particular site have seen little use in soil studies, but they may be employed effectively in such investigations. Suitable programs are also available for suggesting measures of mitigation in cases of soil contamination, and we also consider these. Specific techniques reviewed include: • pattern-recognition techniques [e.g., Principal Components Analysis (PCA), Fuzzy Clustering (FC) and Cluster Analysis (CA); • geostatistical tools [e.g., variograms, Geographical Information Systems (GISs), contour mapping and kriging]; and, • source-identification and contribution-estimation methods [e.g., Positive Matrix Factorization (PMF), and PCA on Absolute Principal Component Scores (PCA/APCS)]. Mitigating measures to limit or to eliminate pollutant sources may be suggested through the use of ranking analysis and multi-criteria decision-making methods (MCDMs), mainly represented in this review by studies employing the Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE) and its associated graphic output, Geometrical Analysis for Interactive Aid (GAIA).

Environmental biodegradation of synthetic polymers II. Biodegradation of different polymer groups

Abstract: We summarize the results of investigations into the biodegradation of different groups of synthetic polymers in various environmental compartments. Most research focused on soil and compost, with polyesters the main object of biodegradation tests. Recognizing the importance of biodegradation in the context of the environment, we summarize the variety of data established by many researchers. We show that some areas have been closely covered, but that aqueous biodegradation especially has been neglected.

Liquid-phase microextraction techniques within the framework of green chemistry

Abstract: This overview deals with the evolution of liquid-phase microextraction (LPME) techniques from their inception in mid-to-late 1990s. We describe and evaluate the most important developments towards implementing greener analytical methodologies focused on the use of less toxic extractant phases, clean energies combined with LPME techniques, new materials (e.g., monolithic silica and nanoparticles), automation of LPME methodologies and recent developments in hyphenation of LPME with a broad variety of analytical techniques.

Ionic liquid-based aqueous two-phase systems and their applications in green separation processes

Abstract: As a new separation technology, ionic liquid (IL)-based aqueous two-phase systems (ATPSs) are attracting the attention of a growing number of scientists and engineers. This article reviews the significant progress that has been made in the field and highlights the possible directions of future developments. We focus on the effects of inorganic salts and ILs on the phase equilibrium of ATPSs, the microstructure of the ATPSs, and their applications in extraction and separation (e.g., small organic molecules, biochemicals, and radiological isotopes). We also address the recovery and the reuse of ILs and the work needed in future.

Molecular fluorescent probes for monitoring pH changes in living cells

Abstract: The availability of synthetic fluorescent probes and the development of powerful new approaches to microscopy have made fluorescence microscopy an essential tool for biomedical science and biology. Intracellular pH plays vital roles in physiological and pathological processes (e.g., receptor-mediated signal transduction, cell growth and apoptosis, ion transport, and homeostasis). Due to the presence of an H+ acceptor linked to the fluorophore, some small molecular fluorescent probes display pH-sensitive absorption and fluorescence emission. Such behavior has been employed to engineer pH indicators for studies of pH regulation in vivo. The review summarizes advances in the creation of novel molecular fluorescent pH probes and their applications in biomedicine and cell biology, especially focusing on the design and the synthesis of small molecular probes for monitoring pH changes in living cells. (C) 2010 Elsevier Ltd. All rights reserved.

Coupling ultra-high-pressure liquid chromatography with mass spectrometry

Abstract: In recent years, different approaches have been taken to improve chromatographic performance in terms of analysis time and/or resolution. The use of columns packed with sub-2μm particles in ultra-high-pressure liquid chromatography (UHPLC) has become a technique of choice in many laboratories. Furthermore, for the analysis of complex matrices (e.g., biological fluids, plant extracts, and food and environmental samples), coupling UHPLC with mass spectrometry (MS) or tandem MS (MS 2 ) provides a powerful analytical tool. This review describes major advances in the field of UHPLC-MS and UHPLC-MS 2 . We strongly emphasize the possibility of speeding up bioanalysis, drug metabolism, and multi-residue screening assays, while maintaining qualitative and quantitative performance equivalent to HPLC-MS and HPLC-MS 2 . We also report the possibility of gaining additional information in metabolomics, using high-resolution UHPLC with a time-of-flight analyzer. The studies summarized are discussed in this review in terms of throughput increases and resolution enhancements afforded by UHPLC. In addition, we highlight the impact of UHPLC conditions on MS detection capabilities (e.g., acquisition rate, limits of detection and matrix effects).

Pressurized liquid extraction: A useful technique to extract pharmaceuticals and personal-care products from sewage sludge

Abstract: We review the determination of pharmaceuticals and personal-care products (PPCPs) in sewage-sludge samples using pressurized liquid extraction (PLE). PLE is a sample-preparation technique that is increasingly used to extract moderately volatile and non-volatile organic contaminants from solid samples. We discuss the principal parameters to be optimized in PLE (e.g., solvent extraction, temperature, pressure and extraction time). We also examine the occurrence of PPCPs in studies where PLE is applied to sewage sludge.

Determination of organophosphorus and organonitrogen pesticides in water samples

Abstract: Pesticides are among the most dangerous environmental pollutants because of their stability, mobility and long-term effects on living organisms. Their presence in sources of drinking water, essential to life, is a particular danger. In water, these compounds can undergo transformations that lead to production of substances of even greater toxicity. Legal regulations in force stipulate the highest permissible level of pesticides and their residues in water samples, so sensitive, selective analytical techniques have to be applied, appropriate to the low levels of the target analytes. One problem associated with the application of organophosphorus and organonitrogen pesticides (OPPs and ONPs) is the need to monitor their levels in the environment, especially in water, in view of their ability to accumulate. The analysis of water samples for the presence of pesticides is fraught with difficulties, since preparation of samples is an arduous, time-consuming process, which can itself give rise to additional contamination and errors. The generally low levels of target analytes and often the complexity of the matrix are further problems with which the analyst has to contend. This article examines the techniques most commonly used for extracting and determining OPPs and ONPs, and discusses the analytical problems arising at each stage of the analytical procedure.

Analytical methods and recent developments in the detection of melamine

Abstract: Melamine (MEL) is an emerging contaminant in milk, infant formula and pet food, and is the subject of much recent research. This review focuses on analytical methods for detecting MEL residue. We present and discuss the advantages, the disadvantages and the applicability of methods, including common techniques [e.g., capillary electrophoresis, high-performance liquid chromatography (HPLC), LC with mass spectrometry (LC-MS), LC with tandem (LC-MS2), gas chromatography with MS (GC-MS), matrix-assisted laser desorption/ionization MS (MALDI-MS), nuclear magnetic resonance spectroscopy, vibrational spectroscopy, chemiluminescence analysis and immunoassay] and several novel detection methods. We propose that the new generation of analytical methods for detecting MEL requires development of powerful analytical devices, combination of multiple techniques, and application of new materials.

The roles of ionic liquids in sorptive microextraction techniques

Abstract: The roles that ionic liquids (ILs) can play as extractants, intermediate solvents, mediators and desorption solvents in liquid-phase and solid-phase microextraction (SPME) provide the topic of this review. We emphasize the added value of using ILs in single-drop microextraction, hollow-fiber-based liquid-phase microextraction, dispersive liquid-liquid microextraction, and in-fiber and in-tube SPME, the most relevant being greater simplicity, greater selectivity, greater extractability and lower consumption of organic solvents. We also give systematic consideration to the requirements of detection as the next step. Further, we outline the unique properties of ILs that are exploited in each extraction procedure. The growing importance of microextraction techniques in sample preparation justifies this approach.

Advances in surface plasmon resonance biosensor technology towards high-throughput food safety analysis

Abstract: Built on the principle of specific biological-recognition measurements coupled with a signal transducer, surface-plasmon-resonance (SPR)-biosensor technology has developed over the past several decades, resulting in commercial production of versatile tools for many applications that greatly impact disciplines from the life sciences to the medical, pharmaceutical, biotechnology and agri-food industries. We review the recent development of SPR optical biosensors towards multiplexing and the coupling of this technology with other emerging ‘-omics’ for high-throughput, food-safety and quality analysis.

Manipulation of droplets in microfluidic systems

Abstract: Since the start of micro total analysis systems, manipulation of droplets in a microfluidic channel has been one of the most important branches of microfluidics The scale of the droplet is remarkably small so that its mixing and reaction are rapid With an array of channels and reliable programming, droplet microfluidics provides a high-throughput platform for applications in chemistry and biology The droplet in a microfluidics system can be seen as an isolated reactor, with low consumption of samples and reagents, minimal dispersion and flexible control We review progress in manipulation of droplets in microfluidic systems and their applications We also discuss future perspectives

Bismuth-modified electrodes for lead detection

Abstract: This review describes the use of electrochemical sensors for lead detection, focusing on sensors modified with bismuth (Bi) that are more “environment friendly” than mercury electrodes. We report and discuss the experimental variables that affect lead measurement using Bi-modified electrodes. We highlight the practical problems of lead contamination encountered during sample treatment and lead detection, in order to give a valid, rounded picture. In addition, we report and discuss different treatments needed for lead detection in natural samples (food, clinical and environmental) using Bi sensors.

Coupling of planar chromatography to mass spectrometry

Abstract: Coupling of planar chromatography to mass spectrometry (MS) and especially ambient MS is a relatively new field of great interest. The direct sample access at ambient conditions and the feasibility to obtain mass spectra free of contamination within a minute or even within seconds greatly contributes to the progress of planar chromatography. Targeted recording of mass spectra on zones of interest is performed after evaluation of the chromatogram, thus providing high efficiency. Reported approaches for coupling are divided into elution-based and desorption-based techniques. Devices of both categories are commercially available. As a consequence of increasing importance, a rethink of the terminology of liquid chromatography with MS has to be considered.

Metabolomics analysis II. Preparation of biological samples prior to detection

Abstract: After discussing the significance of preliminary operations, such as selection or storage of biological samples, we critically review the other steps of the analytical process prior to metabolite detection. First comes interruption of metabolism or quenching, which is of crucial importance in the analysis of biological samples. Then, we consider quantitative extraction of metabolites (selective or total for targeted or global metabolomics analysis, respectively) as a function of sample characteristics: solid or liquid samples and cell culture. Finally, we comment on additional steps, such as preconcentration of metabolites, clean up of extracts and fractionation for metabolite separation, and discuss their inclusion in analytical methods.

Carbon nanostructures for separation, preconcentration and speciation of metal ions

Abstract: Novel carbon-based nanomaterials with unique properties find increasing use in analytical science. This article presents an up-to-date overview of recent applications of carbon nanotubes (CNTs), metal oxide-CNT nanocomposites and carbon-encapsulated magnetic nanoparticles for enrichment and separation of metal ions, and speciation. The sorption mechanism appears to be mainly attributable to chemical interactions between metal ions and the functional groups on the surface. I address the effects of surface oxidation and chemical functionalization, sorption capacities and process parameters, and discuss the application of these new nanomaterials to metal speciation.

Phosphopeptide enrichment using metal oxide affinity chromatography

Abstract: The demand for effective sample preparation strategies that enable the in-depth study of protein phosphorylation has spawned a number of selective affinity techniques that allow enrichment of phosphopeptides from highly complex peptide mixtures. Among those, metal oxide affinity (MOA) materials have seen a strong increase in popularity in recent years, and MOA chromatography is now one of the most widely used strategies in phosphoproteomics. This review gives an overview of the mechanisms of metal oxide–phosphate interaction, discusses strategies to improve enrichment protocols and highlights achievements in characterizing the phosphoproteome with the help of MOA materials.

Metabolomics analysis I. Selection of biological samples and practical aspects preceding sample preparation

Abstract: Metabolomics is one of the most recently emerged “-omics” sciences. Its significance in systems biology is gaining interest to levels similar to proteomics, transcriptomics and genomics. One of the main limitations in metabolomics analysis is the lack of totally comprehensive approaches and in-depth studies, as individuals or laboratories with different skill sets usually develop these. This variability particularly affects sample preparation due to the extensive heterogeneity of biological samples. This two-part review aims to offer a practical guide to preparing biological samples in metabolomics in order to reach the current level in genomics and proteomics. The first part focuses on analytical criteria for sample selection and operations that precede sample preparation.