Application of single-drop microextraction and comparison with solid-phase microextraction and solid-phase extraction for the determination of alpha- and beta-endosulfan in water samples by gas chromatography-electron-capture detection

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. The 98/83 European Directive requires the measurement of pesticides residues at a target concentration of 1.0 microg/l in surface water and 0.1 microg/l in drinking water. In order to reach the level of detection required, efficient extraction techniques are necessary. The application of a new extraction technique: single-drop microextraction (SDME), followed by gas chromatography with electron-capture detection, was assessed for determining alpha-endosulfan and beta-endosulfan in water samples. Experimental parameters which control the performance of SDME, such as selection of microextraction solvent and internal standard, optimization of organic drop volume, effects of sample stirring, temperature and salt addition, and sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity, precision, detection and quantitation limits, plus matrix effects were evaluated. The SDME method was compared with solid-phase microextraction and solid-phase extraction with the aim of selecting the most appropriate method for a certain application.     

Determination of carbamates and organophosphorus pesticides by SDME–GC in natural water

Water contamination due to the wide variety of pesticides used in agriculture practices is a global environmental pollution problem. Analytical methods with low quantification limits are necessary. The application of a new extraction technique, solvent drop microextraction (SDME), followed by gas chromatography with a nitrogen-phosphorus detector, was assessed for determining carbamates and organophosphorus pesticides in natural water. Experimental parameters which control the performance of SDME such as selection of microextraction solvent, optimization of organic drop volume, effects of sample stirring, salt addition, and, finally, sorption time profiles were studied. Once SDME was optimized, analytical parameters such as linearity (r ²>0.99), precision (<13%), and detection limits (0.2 to 5 μg/L), plus matrix effects were evaluated (no matrix effects were found). SDME is a dynamic technique able to extract pesticides from water in 14 min; the use of organic solvents and water samples for SDME is negligible compared to other extraction techniques.     

Optimization of a single-drop microextraction procedure for the determination of organophosphorus pesticides in water and fruit juice with gas chromatography-flame photometric detection

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus pesticides (OPPs) in water and fruit juice by gas chromatography (GC) with flame photometric detection (GC-FPD). The significant parameters affecting the SDME performance such as selection of microextraction solvent, solvent volume, extraction time, stirring rate, sample pH and temperature, and ionic strength were studied and optimized. Two types of SDME mode, static and cycle-flow SDME, were evaluated. The static SDME procedure provided more sensitive analysis of the target analytes. Therefore, static SDME with tributyl phosphate (TBP) as internal standard was selected for the real sample analysis. The limits of detection (LODs) in water for the six studied compounds were between 0.21 and 0.56 ng/mL with the relative standard deviations ranging from 1.7 to 10.0%. Linear response data was obtained in the concentration range of 0.5-50 ng/mL (except for dichlorvos 1.0-50 ng/mL) with correlation coefficients from 0.9995 to 0.9999. Environmental water sample collected from East Lake and fruit juice samples were successfully analyzed using the proposed method, but none of the analytes in both lake water and fruit juice were detected. The recoveries for the spiked water and juice samples were from 77.7 to 113.6%. Compared with the conventional methods, the proposed method enabled a rapid and simple determination of organophosphorus pesticides in water and fruit juice with minimal solvent consumption and a higher concentration capability.     

Multiple headspace single-drop microextraction-a new technique for quantitative determination of styrene in polystyrene

Single-drop microextraction (SDME), an emerging miniaturised extraction technique, was for the first time combined with multiple headspace extraction (MHE) to enable the quantitative determination of volatiles in solid matrixes by SDME technique. The concept of multiple headspace single-drop microextraction (MHS-SDME) was then applied for quantitative determination of styrene in polystyrene (PS) samples. Good linearity for the multiple headspace extraction was obtained when the migration of styrene was facilitated by grinding the samples and incubating them for 1 h at 150 degrees C prior the first extraction. Two microlitres of butyl acetate was used as the single-drop microextraction solvent and the extraction time was 5 min per cycle. The relative standard deviation (RSD) for single-drop microextraction of styrene standard at n=6 was 7.6%. Linearity was shown for styrene concentrations between 0.005 and 0.75 microg/ml (R2=0.999). This corresponds to total amount of styrene between 0.1 and 15 microg. The limit of quantitation for styrene standard at S/N 10 was 0.005 microg/ml. The developed method was validated against and showed good agreement with an earlier reported dissolution-precipitation method.     

Single drop microextraction or solid phase microextraction-gas chromatography-mass spectrometry for the determination of iodine in pharmaceuticals, iodized salt, milk powder and vegetables involving conversion into 4-iodo-N,N-dimethylaniline

A rapid sequence of oxidation and iodination using 2-iodosobenzoate as an oxidizing agent and N,N-dimethylaniline as an iodine scavenger at pH 6.4, when 4-iodo-N,N-dimethylaniline is formed, has been used for the determination of iodide by GC-MS. Solid phase microextraction (SPME) and single drop microextraction (SDME) have been used for the extraction of the iodo-derivative and their relative efficiencies compared. Pharmaceutical samples were subjected to solid phase extraction (SPE) for cleanup and the eluate analyzed for iodide. Iodate in salt samples was reduced to iodide with ascorbic acid. Milk powder and dried vegetables were wet combusted with peroxydisulfate to liberate covalently bound iodine as iodate which was reduced before derivatization. A rectilinear calibration graph was obtained for 0.1 microg-10 mg l(-1) iodide by both extraction methods, the correlation coefficient and limit of detection (LOD) were 0.9995 and 25 ng l(-1) iodide by SPME method, and 0.9998 and 10 ng l(-1) iodide by SDME method, respectively. SDME appeared to be more efficient technique than SPME for the present system. From the pooled data, the average recovery of spiked iodide to real samples was 100.7% (range 96.5-107.0%) with an average R.S.D. of 3.1% (range 2.6-4.5%).     

Solid-phase microextraction versus single-drop microextraction for the analysis of nitroaromatic explosives in water samples.

This paper compares solid-phase microextraction (SPME) with a recently developed extraction method called single-drop microextraction (SDME) for the analysis of nitroaromatic explosives in water samples. The two techniques are examined in terms of procedure, chromatographic analysis and method performance. All practical considerations for both techniques are also reviewed. SPME requires dedicated apparatus and is relatively expensive, as the fiber's lifetime is limited. However, it has the advantages over SDME that it can be easily used for headspace analysis and has lower detection limits for all the target analytes. SDME requires more elaborate manual operations, thus affecting linearity and precision.     

Determination of Six Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC-NPD

A single-drop microextraction (SDME) procedure with a modified microsyringe was developed for the analysis of six organophosphorus pesticides (OPPs) in water. Microsyringe was modified by attaching a 2-mm cone onto the needle tip end. The conditions affecting SDME performance including microextraction solvent, stirring speed, extraction time, ionic strength and sample pH were optimized. Under the optimized conditions, the linear ranges of the SDME with ethion as internal standard were 0.05–50 μg L^?1 (except for dimethoate 5–5,000 μg L^?1) and limits of detection (LOD) were 0.012–0.020 μg L^?1 (except for dimethoate 0.45 μg L^?1). Recoveries of six pesticides were in the range of 70.6–107.5 % with relative standard deviation lower than 6.0 %. The modified method is simple, rapid and sensitive, and acceptable in the analysis of OPPs pesticides in water samples.     

Comparison of Hollow Fiber and Single-Drop Liquid-Phase Microextraction Techniques for HPLC Determination of Aniline Derivatives in Water

The development of rapid, inexpensive, and environmentally friendly sample-preparation techniques is a serious issue in chemical analysis. This explains the success of two new miniaturized liquid-phase microextraction techniques used as sample-preconcentration techniques for liquid chromatography – hollow fiber and single-drop liquid-phase microextraction. In hollow-fiber-based microextraction (HFME) a hollow fiber is filled with an organic solvent to establish and protect micro volumes of acceptor solution. This attractive, simple, low cost method, which is highly selective and enables substantial enrichment, has been compared with single-drop microextraction (SDME), using four aniline derivatives (3-chloroaniline, 3-bromoaniline, 2-nitroaniline, and 4-nitroaniline) as model compounds. The most important conditions and practical considerations for method optimization are discussed. The results showed that enrichment factors varied from 91.0 to 180.1 for SDME and from 106.43 to 286.33 for HFME. Extraction times were approximately equal. Stirring speeds selected for SDME and HFME were 800 and 900 rev min^?1, respectively. Other quantitative data were almost identical.     

分散液相微萃取技术研究进展

分散液相微萃取是最近发展起来的一种新型样品前处理技术,该方法操作简单、成本低、富集效率高、所需有机溶剂用量极少,是一种环境友好的液相微萃取新技术.与悬滴液相微萃取和中空纤维液相微萃取相比,萃取时间大为缩短.分散液相微萃取可与气相色谱、液相色谱和原子吸收分光光度计等仪器联用,并已在环境样品、食品样品分析中得到了较广泛的应用.本文对分散液相微萃取的基本原理、影响富集效率的因素和目前的应用研究进展进行了评述.     

Simultaneous Analysis of Carbamate and Organophosphorus Pesticides in Water by Single-Drop Microextraction Coupled with GC–MS

Single-drop microextraction (SDME) has been coupled with gas chromatography–mass spectrometry to enable rapid and simple simultaneous analysis of carbamate and organophosphorus pesticides (OPP). The significant conditions affecting SDME performance (microextraction solvent, extraction time, solvent volume, sample pH, stirring speed, and ionic strength) were studied and optimized. Extraction was achieved by suspending a 1.5-μL drop of toluene from the tip of a microsyringe directly immersed in 5-mL aqueous donor solution at pH 5 stirred at 800 rpm. The dynamic linear range and detection limits of the method were evaluated by analysis of water samples spiked with carbamate pesticides and OPP. Under selected ion-storage mode, very low detection limits (0.02–0.50 ng mL^?1) and good linearity (0.5–200 ng mL^?1) were achieved. When SDME was applied to analysis of pesticides in natural water samples good recoveries (89.4–102.1%) were obtained. Inter-day and intra-day RSD of most results were below 5.4 and 6.1%, respectively. The method proved to be a rapid and simple tool for extraction and analysis of these pesticides in water samples.     

Recent developments in headspace microextraction techniques for the analysis of environmental contaminants in different matrices

Headspace microextraction procedures such as solid-phase microextraction (SPME) and single drop microextraction (SDME) or liquid-phase microextraction (LPME) are increasingly used for the extraction of environmental organic pollutants from a variety of aqueous, viscous, semisolid and solid environmental and biological matrices. In this article, recent analytical applications of these methodologies when used as an isolation and trace enrichment step prior to the analysis of organic pollutants (pesticides, polycyclic aromatic hydrocarbons, polychlorinated compounds, organotin compounds, phenolic derivatives, aromatic amines, phthalates, etc.) by gas and liquid chromatography are reviewed. The applicability and inherent limitations of headspace microextraction are also discussed. The future direction of research in this field and general trends toward commercial applications are considered.     

Development and applications of single-drop microextraction for pesticide residue analysis: A review

Single-drop microextraction (SDME) has become more popular than other microextraction techniques because it is simple, cost-effective, easy to operate and nearly solvent-free. The technique has been employed successfully for trace analysis in environmental, biomedical and food applications. In view of the increasingly stringent regulatory limits for many pesticides, which are below the LOD of the existing instruments, SDME may provide a cost-effective solution for reducing the LOD of pesticides. The present review focuses on recent development in SDME technique, and its application coupled with various analytical techniques, such as GC-MS, GC and HPLC for pesticide residue analysis in different matrices. The advantages, limitations and outlook on the future of SDME technique for its wider applications are also discussed.     

Liquid–Liquid Extraction of Organic Compounds into a Single Drop of the Extractant: Overview of Reviews

Single-drop microextraction (SDME) and hollow-fiber membrane microextraction (HFME) belong to methods of the liquid-phase microextraction preconcentration of organic compounds. These methods are characterized by the low consumption of organic solvents, high preconcentration factors, simplicity, low cost, ease of combination with various chromatographic methods; processes of preconcentration and sample injection are combined in a single device. Since the emergence of SDME (1996) and HFME (1999), a large number of versions have been developed that differ in the preconcentration technique, nature of the extractants used, and combinations with methods for the subsequent determination of the preconcentrated substances. The popularity of these methods among the analysts is evidenced by many reviews that we have summarized in this publication.

     

Single-drop microextraction as a powerful pretreatment tool for capillary electrophoresis: A review

Single drop microextraction (SDME) is a convenient and powerful preconcentration and sample cleanup method for capillary electrophoresis (CE). In SDME, analytes are typically extracted from a sample donor solution into an acceptor drop hanging at the inlet tip of a capillary. The enriched drop is then introduced to the capillary for CE analysis. Since the volume of the acceptor drop can be as small as a few nanoliters, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In addition, by covering the acceptor phase with an organic layer or by using an organic acceptor phase, inorganic ions such as salts in the sample solution can be blocked from entering the acceptor phase, providing desalting effects. Here, we describe the basic principles and instrumentation for SDME and its coupling with CE. We also review recent developments and applications of SDME-CE.     

Developments in single-drop microextraction

Single-drop microextraction (SDME) has become a very popular liquid-phase microextraction technique because it is inexpensive, easy to operate and nearly solvent-free. Essentially, SDME combines extraction (and conceivably, cleanup) and concentration in a minimum number of steps, and thereafter, direct extract introduction into an analytical system. In this review, in order to encourage further development of SDME, we focus on its recent developments in its various guises. Its applications when used in combination with different analytical techniques, such as gas chromatography, high-performance liquid chromatography, inductively-coupled plasma mass spectrometry, capillary electrophoresis, mass spectrometry and electrothermal atomic absorption spectrometry, are summarized. SDME does have some limitations, and these are also discussed as well. Finally, an outlook on the future of the technique is given.     

Characterization of pathogenic bacteria using ionic liquid via single drop microextraction combined with MALDI-TOF MS

The present research was based on the single drop microextraction (SDME) approach using an ionic liquid drop to extract bacteria from aqueous samples for characterization of pathogenic bacteria by MALDI-TOF MS. The SDME of bacteria from aqueous samples was successfully achieved by using platinum nanoparticles mixed in ionic liquid (IL, 1-butyl-3-methylimidazolium hexafluorophosphate) and IL alone as the extraction drops. The IL was used as liquid drops by SDME to obtain protein profiles from bacteria. Significant numbers of biomarker protein peaks of bacteria were identified from target biological samples. The IL also significantly improved the signal reproducibility of spectra using the SDME approach combined with MALDI-TOF MS. Thus, the present technique was successfully applied to detect pathogenic bacteria at low concentrations of 10(6) cfu mL(-1) from aqueous suspensions. The selected bacteria viz., Escherichia coli and Serratia marcescens were used as target biological sample.     

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.     

Immersed single-drop microextraction interfaced with sequential injection analysis for determination of Cr(VI) in natural waters by electrothermal-atomic absorption spectrometry

Single-drop microextraction (SDME) and sequential injection analysis have been hyphenated for ultratrace metal determination by Electrothermal-Atomic Absorption Spectrometry (ETAAS). The novel method was targeted on extraction of the Cr(VI)-APDC chelate and encompasses the potential of SDME as a miniaturized and virtually solvent-free preconcentration technique, the ability of sequential injection analysis to handle samples and the versatility of furnace autosamplers for introducing microliter samples in ETAAS.     

Simultaneous derivatization and extraction of primary amines in river water with dynamic hollow fiber liquid-phase microextraction followed by gas chromatography-mass spectrometric detection

A one-step derivatization and extraction technique for the determination of primary amines in river water by liquid-phase microextraction (LPME) is presented. In this method the primary amines are derivatized with pentafluorobenzaldehyde (PFBAY) in aqueous solution and extracted by dynamic hollow fiber-protected-LPME (HF-LPME) simultaneously. The effects of solvent selection, sample agitation, extraction time, extraction temperature and salt concentration on the extraction performance are investigated. High enrichments (172-244-fold) and good repeatabilities (RSD less than 7.2%) were obtained. Linearity in this developed method was ranging from 1 to 500 ng/ml, and the correlation coefficients (R2) were between 0.992 and 0.998. Comparisons of sensitivity and precision between dynamic HF-LPME and single-drop liquid-phase microextraction (SDME) were also made.     

Application of single-drop microextraction coupled with gas chromatography for the determination of multiclass pesticides in vegetables with nitrogen phosphorus and electron capture detection

In the present work the single-drop microextraction (SDME) technique coupled with GC-NPD and GC-ECD was evaluated for the determination of multi-class pesticides in vegetables. The donor sample solution preparation was optimized by testing different mixtures of solvents and dilutions with water. The SDME procedure was optimized by controlling drop organic solvent, drop volume, agitation, and exposure time. The optimum sample preparation was achieved with the use of a mixture of acetone/H(2)O (10/90, v/v) in donor sample solution preparation and the consequent SDME using a toluene drop under mild stirring for 25min. The efficiency of the extraction process was studied in fortified tomato and courgette samples and matrix effects were further estimated. The proposed method showed good linearity, limits of detection at the sub-microgkg(-1) level and high precision (RSD <15%) and was applied with success in real vegetable samples showing that SDME can be a promising way for sample preparation in pesticide residue analysis.