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.     

Single drop microextraction—Development,applications and future trends

Single drop microextraction (SDME) has emerged over the last 10–15 years as one of the simplest and most easily implemented forms of micro-scale sample cleanup and preconcentration. In the most common arrangement, an ordinary chromatography syringe is used to suspend microliter quantities of extracting solvent either directly immersed in the sample, or in the headspace above the sample. The same syringe is then used to introduce the solvent and extracted analytes into the chromatography system for identification and/or quantitation. This review article summarizes the historical development and various modes of the technique, some theoretical and practical aspects, recent trends and selected applications.     

Critical evaluation of microextraction pretreatment techniques – Part 1: Single drop and sorbent‐based techniques

Sample pretreatment techniques or preconcentration constitute a very important step before the analysis of environmental, clinical, pharmaceutical, and other complex samples. Thanks to extraction techniques it is possible to achieve higher method sensitivities and selectivities. Miniaturization microextraction methods make them more environmentally friendly and only small amounts of samples are required. In the past 30 years, a number of microextraction methods have been developed and used and are documented in thousands of articles. Many reviews have been written focusing on their use in specified professional fields or on the latest trends. Unfortunately, no uniform nomenclature has been introduced for these methods. Therefore, this review attempts to classify all the essential microextraction techniques and describes their advantages, disadvantages, and the latest innovations. The methods are divided into two main groups: single drop and sorbent‐based techniques according to the type of extraction phase.     

Automation of static and dynamic non-dispersive liquid phase microextraction. Part 1: Approaches based on extractant drop-, plug-, film- and microflow-formation

Simplicity, effectiveness, swiftness, and environmental friendliness – these are the typical requirements for the state of the art development of green analytical techniques. Liquid phase microextraction (LPME) stands for a family of elegant sample pretreatment and analyte preconcentration techniques preserving these principles in numerous applications. By using only fractions of solvent and sample compared to classical liquid–liquid extraction, the extraction kinetics, the preconcentration factor, and the cost efficiency can be increased. Moreover, significant improvements can be made by automation, which is still a hot topic in analytical chemistry. This review surveys comprehensively and in two parts the developments of automation of non-dispersive LPME methodologies performed in static and dynamic modes. Their advantages and limitations and the reported analytical performances are discussed and put into perspective with the corresponding manual procedures. The automation strategies, techniques, and their operation advantages as well as their potentials are further described and discussed.     

用于化学毒剂检测的微萃取技术研究进展

对化学毒剂及其降解产物的分析检测是准确鉴别化学沾染的重要手段。由于化学毒剂及其降解产物的样品可能存在于各种基质中,且部分化学毒剂在水体等基质中降解速度过快,所以将痕量样品从复杂基质中快速高效的富集提取出来显得尤其重要。微萃取技术具有装置体积小、使用少量或不使用溶剂、绿色环保、易与色谱分析技术联用等突出优势受到广泛的关注,并且在含化学毒剂环境样品的前处理过程中得到大量的应用。本文介绍了基于固相和液相萃取剂的多种微萃取技术,并综述了固相微萃取和液相微萃取技术应用于化学毒剂及其降解产物检测方面的研究进展。     

微萃取技术在环境分析中的应用

微萃取技术是近年来出现的绿色样品前处理技术。它具有操作简便、环境友好等优点,并且在环境、医药及食品等领域得到广泛的应用。本文仅就固相微萃取和液相微萃取在环境分析中的应用作一简要综述。     

A glance at achievements in the coupling of headspace and direct immersion single‐drop microextraction with chromatographic techniques

The present article offers a glance at achievements in single‐drop microextraction(SDME), with a focus on the two most commonly used modes of this technique: headspace and direct immersion. Factors affecting SDME, such as the pH and ionic strength of the sample solution, the stirring rate, and the extraction time are briefly summarized. The requirements for the acceptor phase and the influence of the sampling temperature are presented. In addition, the potential of the application of microwave and ultrasonic energy in SDME is also discussed. Examples of the application of the headspace and direct immersion modes of SDME are given in a table as additional Supporting Information.     

Recent development in liquid phase microextraction for determination of trace level concentration of metals—A review

As the drive towards green extraction methods has gained momentum in recent years, it has not always been possible to eliminate organic solvents completely. However, the volumes employed have been reduced remarkably, so that a single microdrop is sufficient in some cases. This effort has led to the development of various liquid phase microextractions namely single drop microextraction (SDME), hollow fiber liquid phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME) and solidified floating organic drop microextraction (SFODME). In this review, the historical development and overview of these miniaturized liquid phase extraction methodologies have briefly been discussed and a comprehensive collection of application of the these methods in combination with different analytical techniques for preconcentration and determination of ultra trace amounts of metals and organometal ions in various matrices have been summarized.     

Automation of static and dynamic non-dispersive liquid phase microextraction. Part 2: Approaches based on impregnated membranes and porous supports

A critical overview on automation of modern liquid phase microextraction (LPME) approaches based on the liquid impregnation of porous sorbents and membranes is presented. It is the continuation of part 1, in which non-dispersive LPME techniques based on the use of the extraction phase (EP) in the form of drop, plug, film, or microflow have been surveyed.     

分散液液微萃取-气相色谱法测定水样中甲拌磷农药

建立了基于分散液液微萃取(DLLME)的新型样品前处理方法,并采用气相色谱/氢火焰离子化检测器对水样中痕量的甲拌磷农药进行了测定。考察了影响分散液液微萃取的因素包括萃取溶剂、分散剂、样品体积、萃取温度和离心速度等。在最佳实验条件下,对甲拌磷的富集倍数达到300倍;检出限为0.001μL/L;方法的线性范围为0.01~10μL/L,R2为0.9986;相对标准偏差为6.65%;回收率为104%。将分散液液微萃取法与单滴液相微萃取和离子液体-液相微萃取方法进行了对比,结果表明,分散液液微萃取技术具有操作简单、快捷(前处理时间小于5 min)、富集效果好、回收率高等优点。同时预言,将离子液体与分散液液微萃取结合,将会产生更加满意的结果。     

Application of new approaches to liquid-phase microextraction for the determination of emerging pollutants

Liquid-liquid extraction (LLE) has been widely used as a pre-treatment technique for separation and preconcentration of organic analytes from aqueous samples. Nevertheless, this technique has several drawbacks, mainly in the use of large volumes of solvents, making LLE an expensive, environmentally-unfriendly technique.Miniaturized methodologies [e.g., liquid-phase microextraction (LPME)] have arisen in the search for alternatives to conventional LLE, using negligible volumes of extracting solvents and reducing the number of steps in the procedure. Developments have led to different approaches to LPME, namely single-drop microextraction (SDME), hollow-fiber LPME (HF-LPME), dispersive liquid-liquid microextraction (DLLME) and solidified floating organic drop microextraction (SFODME).This overview focuses on the application of these microextraction techniques to the analysis of emerging pollutants.     

Recent trends in replacement of disperser solvent in dispersive liquid-liquid microextraction methods

Since its innovation in 2006, the dispersive liquid-liquid microextraction (DLLME) method has attracted the attention of analytical chemists in the field of sample preparation. This method has been successfully applied to determine trace amounts of pollutants in various matrices, but the restriction in the choice of suitable disperser and extraction solvents, and high disperser solvent consumption leading to decreased partition coefficients of the analytes between aqueous phase and extractant are its problems. To solve these drawbacks and develop environmentally friendly techniques, various alternatives for the conventional DLLME have been presented. The current review will begin with an introduction to the sample preparation, implementation of DLLME, and its advantages. Then, we focus on its drawbacks, which result mainly from the use of disperser solvent. Afterward, some of the most interesting approaches that have been employed and published until now are reviewed. Finally, an outlook on the future of these techniques will be given.     

Recent Applications of Molecularly Imprinted Polymers (MIPs) on Micro-extraction Techniques

Microextraction is considered as one of the most critical steps in the entire analytical process because it can effectively remove interference and pre-concentrate the target analytes. Molecularly imprinted polymers (MIPs) are synthetic polymers with a predetermined selectivity for a given analyte, or group of structurally related compounds, which are excellent materials for sample preparation in the process of microextraction owing to their high selectivity and ability. This review provides a critical overview of the synthesis and characterization of MIPs, with a focus on recent applications in the field of solid-phase microextraction (SPME) and liquid-phase microextraction (LPME). The advantages and drawbacks of the applications of MIPs used in SPME and LPME as well as the future expected trends are also discussed.     

Application of solid-phase microextraction in analytical toxicology

Solid-phase microextraction (SPME) is a miniaturized and solvent-free sample preparation technique for chromatographic–spectrometric analysis by which the analytes are extracted from a gaseous or liquid sample by absorption in, or adsorption on, a thin polymer coating fixed to the solid surface of a fiber, inside an injection needle or inside a capillary. In this paper, the present state of practical performance and of applications of SPME to the analysis of blood, urine, oral fluid and hair in clinical and forensic toxicology is reviewed. The commercial coatings for fibers or needles have not essentially changed for many years, but there are interesting laboratory developments, such as conductive polypyrrole coatings for electrochemically controlled SPME of anions or cations and coatings with restricted-access properties for direct extraction from whole blood or immunoaffinity SPME. In-tube SPME uses segments of commercial gas chromatography (GC) capillaries for highly efficient extraction by repeated aspiration–ejection cycles of the liquid sample. It can be easily automated in combination with liquid chromatography but, as it is very sensitive to capillary plugging, it requires completely homogeneous liquid samples. In contrast, fiber-based SPME has not yet been performed automatically in combination with high-performance liquid chromatography. The headspace extractions on fibers or needles (solid-phase dynamic extraction) combined with GC methods are the most advantageous versions of SPME because of very pure extracts and the availability of automatic samplers. Surprisingly, substances with quite high boiling points, such as tricyclic antidepressants or phenothiazines, can be measured by headspace SPME from aqueous samples. The applicability and sensitivity of SPME was essentially extended by in-sample or on-fiber derivatization. The different modes of SPME were applied to analysis of solvents and inhalation narcotics, amphetamines, cocaine and metabolites, cannabinoids, methadone and other opioids, fatty acid ethyl esters as alcohol markers, γ-hydroxybutyric acid, benzodiazepines, various other therapeutic drugs, pesticides, chemical warfare agents, cyanide, sulfide and metal ions. In general, SPME is routinely used in optimized methods for specific analytes. However, it was shown that it also has some capacity for a general screening by direct immersion into urine samples and for pesticides and other semivolatile substance in the headspace mode.     

Recent advances of green pretreatment techniques for quality control of natural products

A few advancing technologies for natural product analysis have been widely proposed, which focus on decreasing energy consumption and developing an environmentally sustainable manner. These green sample pretreatment and analysis methods following the green Analytical Chemistry (GAC) criteria have the advantage of improving the strategy of chemical analyses, promoting sustainable development to analytical laboratories, and reducing the negative effects of analysis experiments on the environment. A few minimized extraction methodologies have been proposed for replacing the traditional methods in the quality evaluation of natural products, mainly including solid-phase microextraction (SPME) and liquid phase microextraction (LPME). These procedures not only have no need for large numbers of samples and toxic reagent, but also spend a small amount of extraction and analytical time. This overview aims to list out the main green strategies on the application of quality evaluation and control for natural products in the past 3 years.     

Novel capsule phase microextraction in combination with high performance liquid chromatography with diode array detection for rapid monitoring of sulfonamide drugs in milk

Capsule phase microextraction is introduced herein for the first time to determine four sulfonamide residues in milk samples (sulfanilamide, sulfadiazine, sulfamethizole, and sulfathiazole). The technique eloquently integrates filtration and stirring mechanism into the extraction device, as such no filtration of the sample is needed prior to introducing the extraction device into the sample, and when placed on a magnetic stirrer, the device spins itself in order to diffuse the sample, resulting in faster extraction equilibrium. Microextraction capsules consist of three main parts; a magnet, a cellulose fiber substrate coated with high performance sol‐gel hybrid organic‐inorganic sorbent, and a porous membrane. Various encapsulated sol‐gel sorbents were tested in standard solutions prepared in deionized water and milk samples under different operational conditions. Analyte extraction time and elution time, type of sol‐gel sorbent, elution solvent, as well as the ratio of the sorbent to the elution solvent were among the optimized conditions. The protocols that yielded the best absolute recovery rates were subsequently tested in various milk samples. Method validation was performed in terms of linearity, accuracy and precision, reusability and ruggedness using the Youden test. The examined sulfonamides were subsequently analysed by reversed phase high performance liquid chromatography with diode array detection.     

Examination of n=2 reaction mechanisms that reproduce pH-dependent reduction potentials

This work describes a new sampling method termed directly suspended droplet microextraction (DSDME) was developed. In this technique a free microdroplet of solvent is delivered to the surface of an immiscible aqueous sample while being agitated by a stirring bar placed on the bottom of the sample cell. After some time, the microdroplet of solvent is withdrawn by a syringe and analyzed. Under the proper stirring conditions, the suspended droplet can remain in a top-center position of the aqueous sample. The droplet can become partly engulfed within the sample while maintaining a stable shape with mechanical equilibrium and the mass transfer could be effectively intensified. Using 1,8-dioxyanthraquinone as a model compound and 1-octanol as the solvent, the extraction performance was investigated using HPLC. Since DSDME is based on a self-stable single microdroplet system, there are no requirements for special equipment or other supporting material like hollow fibers. Other advantages include ease of operation, free from cross contamination, quick to reach extraction equilibrium, and the ability to be combined with various analysis instruments. In our experiments, good linearity (r² = 0.9992) and precision (R.S.D. < 1%, n = 5) were achieved. DSDME is a promising pre-treatment method for the fast analysis of trace components in complicated matrices.     

Comparison of solid-phase and single-drop microextractions for headspace analysis of herbal essential oils

The analytical microextraction methods of gas chromatography coupled with flame ionisation detector (GC-FID) for determination of selected essential oils in herbs were proposed. Two microextraction methods for the isolation of essential oils from plants such as Lavandula spica L., Melissa officinalis L., Mentha piperita L. and Salvia officinalis L. were used. The methods of solid-phase and single-drop microextractions, were optimised and compared. The obtained LOD values for all studied essential oils were found to be within 2.5–20.5 μg for SDME and 57.0–139.8 μg for SPME method per 100 g of dried sample leaves. The appropriate LOQ values were then 8.4–68.4 μg for SDME and 189.8–466.1 μg for SPME of target analytes per 100 g of dried sample leaves.      

Dispersive liquid-liquid microextraction versus single-drop microextraction for the determination of several endocrine-disrupting phenols from seawaters

Two liquid-phase microextraction procedures: single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), have been developed for the determination of several endocrine-disrupting phenols (EDPs) in seawaters, in combination with high-performance liquid chromatography (HPLC) with UV detection. The EDPs studied were bisphenol-A, 4-cumylphenol, 4-tertbutylphenol, 4-octylphenol and 4-n-nonylphenol. The optimized SDME method used 2.5 μL of decanol suspended at the tip of a micro-syringe immersed in 5 mL of seawater sample, and 60 min for the extraction time. The performance of the SDME is characterized for average relative recoveries of 102 ± 11%, precision values (RSD) < 9.4% (spiked level of 50 ng mL⁻¹), and detection limits between 4 and 9 ng mL⁻¹. The optimized DLLME method used 150 μL of a mixture acetonitrile:decanol (ratio 15.7, v/v), which is quickly added to 5 mL of seawater sample, then subjected to vortex during 4 min and centrifuged at 2000 rpm for another 5 min. The performance of the DLLME is characterized for average relative recoveries of 98.7 ± 3.7%, precision values (RSD) < 7.2% (spiked level of 20 ng mL⁻¹), and detection limits between 0.2 and 1.6 ng mL⁻¹. The efficiencies of both methods have also been compared with spiked real seawater samples. The DLLME method has shown to be a more efficient approach for the determination of EDPs in seawater matrices, presenting enrichment factors ranging from 123 to 275, average relative recoveries of 110 ± 11%, and precision values (RSD) < 14%, when using a real seawaters (spiked level of 3.5 ng mL⁻¹).     

New developments in microextraction techniques in bioanalysis. A review

In recent years, the interest in new extraction methods with lower sample volume requirements, simpler equipment and handling, and lower reagent consumption, has led to the development of a series of microextraction methods based on extraction phases in the microliter order. Nowadays, many references can be found for several of these methods, which imply a wide range of applications referred to both the analyte and the sample nature. In this paper, recent developments in both well-established microextraction techniques (solid phase microextraction, hollow-fiber liquid phase microextraction, dispersive liquid–liquid microextraction, etc.) and recently appeared microextraction procedures (nanoextraction systems, microchip devices, etc.) for the clinical analysis of biological samples will be reviewed and discussed.