Methods for determination of polybrominated diphenyl ethers in environmental samples - review

Polybrominated diphenyl ethers (PBDEs) are a group of persistent organic pollutants. They are used as flame retardants in plastics, paints, varnishes and textile materials. PBDEs pose great risk to the environment because of their high persistence and ability to get into the environment easily due to the lack of chemical bonds with the matrix of materials, to which they are added. Global research studies confirmed the occurrence of those compounds in the majority of elements of water and land environment. Analysis of PBDEs in environmental samples is one of the specific analytical methods of criteria that comprise low detection limits and high selectivity. The analysis of PBDEs in environmental samples is one of the specific analytical methods, in which the main criteria are low detection limits and high selectivity. In this article, a literature review of methods for environmental sample preparation and analysis of the PBDE content was presented. The article discusses the potential of modern extraction techniques such as: solid-phase microextraction, single-drop microextraction, dispersive liquid-liquid microextraction, microwave-assisted extraction, cloud point extraction, hollow fibre-liquid phase microextraction and others for the separation of PBDEs from environmental samples with a complex matrix. Among the methods for qualitative and quantitative determination of PBDEs, a particular focus was put on gas chromatography/mass spectrometry with various injection techniques and different types of sample ionisation.     

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.     

一滴溶剂微萃取-毛细管气相色谱法分析水中的七种硝基苯类化合物

用一滴溶剂微萃取(SDME)-毛细管气相色谱联用技术测定水中的硝基苯、硝基甲苯类和硝基氯苯类化合物,对影响萃取的因素如萃取溶剂种类、液滴体积、搅拌速度、针尖入水深度、水样体积、萃取时间、萃取温度等进行了优化,结果表明:硝基苯和硝基甲苯类化合物在0.8～32 μg/L 范围内,硝基氯苯类化合物在0.04～3.2 μg/L 范围内均呈现良好的线性(r2>0.999),检出限可达0.01～0.3 μg/L。自来水加标样品测定的相对标准偏差和平均回收率(n=5)范围分别为3.1%～7.9%和101%～105%,废水加标样品测定的相对标准偏差和平均回收率(n=5)范围分别为3.3%～7.9%和92.5%～97.0%。优化后的SDME具有环保、灵敏、快速、简便等特点,适用于萃取水中的痕量硝基苯、硝基甲苯类和硝基氯苯类化合物。     

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.     

Griess micro-assay for the determination of nitrite by combining fibre optics-based cuvetteless UV-Vis micro-spectrophotometry with liquid-phase microextraction

A novel, simple and low cost method for the determination of nitrite using headspace single-drop microextraction and cuvetteless ultraviolet-visible micro-spectrophotometry is described. A Griess reagent-containing aqueous microdrop exposed to the headspace was used as extractant of the volatile nitrogen oxides generated from nitrite by direct acidification of the aqueous sample. Experimental parameters affecting the headspace single-drop microextraction performance such as composition and volume of the extractant phase, sample volume, concentration of acetic acid, ionic strength, sample agitation, temperature and microextraction time were systematically examined. Measurements were carried out at 540 nm under optimized conditions. A detection limit of 1.5 μg L⁻¹ and an enrichment factor of 193 were achieved. Intra-day repeatability and inter-day reproducibility, expressed as relative standard deviation, were 3.5% (n = 7) and 10.6% (three consecutive days), respectively. The proposed method, characterized by its enhanced sensitivity and selectivity in comparison with the standardized colorimetric assay, was successfully applied to the analysis of several environmental water samples.     

Combining gold nanoparticle-based headspace single-drop microextraction and a paper-based colorimetric assay for selenium determination

Analytical and Bioanalytical Chemistry - A novel method combining headspace single-drop microextraction with a paper-based colorimetric assay was developed. Headspace single-drop microextraction...     

Comparison of headspace and direct single-drop microextraction and headspace solid-phase microextraction for the measurement of volatile sulfur compounds in beer and beverage by gas chromatography with flame photometric detection

Three approaches based on headspace single-drop microextraction (HS-SDME), direct single-drop microextraction (Direct-SDME), and headspace solid-phase microextraction (HS-SPME), have been compared for analyzing volatile sulphur compounds (VSCs) in beer and beverage. Procedures and performance of the three methods have been contrasted through the determination of extraction efficiencies, precision, linearity and limits of detection. The overall process of HS-SDME and HS-SPME was applied to GC-FPD determination of five VSCs in beer and beverage.     

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.     

Headspace single-drop microextration for the detection of organotin compounds

The performance of single-drop microextraction (SDME), coupled with gas chromatography/mass spectrometry, was assessed for the determination of tributyltin compounds in water and solid samples. Experimental parameters impacting the performance of SDME, such as microextraction solvent and sampling and stirring time, were investigated. Analytical results obtained by SDME were compared with those generated by conventional solid phase microextraction (SPME) and liquid-liquid extraction (LLE) for the determination of TBT in PACS-2 sediment certified reference material (CRM).     

Fast analysis of volatile components of Achillea tenuifolia Lam with microwave distillation followed by headspace single-drop microextraction coupled to gas chromatography-mass spectrometry (GC–MS)

This article investigates the effect of microwaves on the amount of volatile compounds Achillea tenuifolia Lam with two methods, headspace single-drop microextraction and microwave-assisted headspace single-drop microextraction (MA-SDME), for the analysis of essential oil. Solvent selection, solvent volume, microwave power, irradiation time and sample mass were optimised by the simplex method.     

Miniaturized preconcentration methods based on liquid–liquid extraction and their application in inorganic ultratrace analysis and speciation: A review

Liquid–liquid extraction (LLE) is widely used as a pre-treatment technique for separation and preconcentration of both organic and inorganic analytes from aqueous samples. Nevertheless, it has several drawbacks, such as emulsion formation or the use of large volumes of solvents, which makes LLE expensive and labour intensive. Therefore, miniaturization of conventional liquid–liquid extraction is needed. The search for alternatives to the conventional LLE using negligible volumes of extractant and the minimum number of steps has driven the development of three new miniaturized methodologies, i.e. single-drop microextraction (SDME), hollow fibre liquid-phase microextraction (HF-LPME) and dispersive liquid–liquid microextraction (DLLME). The aim of this paper is to provide an overview of these novel preconcentration approaches and their potential use in analytical labs involved in inorganic (ultra)trace analysis and speciation. Relevant applications to the determination of metal ions, metalloids, organometals and non-metals are included.     

Critical review on recent developments in solventless techniques for extraction of analytes

The most recent contributions on solventless extraction techniques have been reviewed. This paper deals with those techniques that use solid phases, such as solid-phase microextraction, liquid phases, such as single-drop microextraction and hollow-fibre liquid-phase microextraction, and subcritical fluids, such as subcritical water extraction. In all cases, the most recent publications have been critically studied. Direct extraction and derivatization processes to facilitate the extraction of analytes in different areas have been included. Hyphenated approaches, if available, are also included in this review. Comparison of techniques organized by analytes and matrices also enhances this critical overview of solventless techniques.     

Dispersive liquid-liquid microextraction followed by reversed phase HPLC for the determination of decabrominated diphenyl ether in natural water

A simple, rapid, and efficient method, dispersive liquid-liquid microextraction (DLLME), has been developed for the extraction and preconcentration of decabrominated diphenyl ether (BDE-209) in environmental water samples. The factors relevant to the microextraction efficiency, such as the kind and volume of extraction and dispersive solvent, the extraction time, and the salt effect, were optimized. Under the optimum conditions (extraction solvent: tetrachloroethane, volume, 22.0 microL; dispersive solvent: THF, volume, 1.00 mL; extraction time: below 5 s and without salt addition), the most time-consuming step is the centrifugation of the sample solution in the extraction procedure, which is about 2 min. In this method, the enrichment factor could be as high as 153 in 5.00 mL water sample, and the linear range, correlation coefficient (r(2)), detection limit (S/N = 3), and precision (RSD, n = 6) were 0.001-0.5 microg/mL, 0.9999, 0.2 ng/mL, and 2.1%, respectively. This method was successfully applied to the extraction of BDE-209 from tap, East Lake, and Yangtse River water samples; the relative recoveries were 95.8, 92.9, and 89.9% and the RSD% (n = 3) were 1.9, 2.7, and 3.5%, respectively. Comparison of this method with other methods, such as solid-phase microextraction (SPME), and single-drop microextraction (SDME), indicates that DLLME is a simple, fast, and low-cost method for the determination of BDE-209, and thus has tremendous potential in polybrominated diphenyl ethers (PBDEs) residual analysis in environmental 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.     

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.     

On-line coupling of ionic liquid-based single-drop microextraction with capillary electrophoresis for sensitive detection of phenols

An ionic liquid-based single-drop microextraction (IL-SDME) procedure using IL as an extractant on-line coupled to capillary electrophoresis (CE) is proposed. The method is capable of quantifying trace amounts of phenols in environmental water samples. For the SDME of three phenols, a 2.40 nL IL microdrop was exposed for 10 min to the aqueous sample and then was directly injected into the capillary column for analysis. Extraction parameters such as the extraction time, the IL single-drop volume, pH of the sample solution, ionic strength, volume of the sample solution and the extraction temperature were systematically investigated. Detection limits to three phenols were less than 0.05 μg mL⁻¹, and their calibration curves were all linear (R² ≥ 0.9994) in the range from 0.05 to 50 μg mL⁻¹. And enrichment factors for three phenols were 156, 107 and 257 without agitation, respectively. This method was then utilized to analyze two real environmental samples from Yellow River and tap water, obtaining satisfactory results. Compared with the usual SDME for CE, IL-SDME–CE is a simple, low-cost, fast and environmentally friendly preconcentration technique.     

Basic principles,recent trends and future directions of microextraction techniques for the analysis of aqueous environmental samples

Microextraction-based sample preparation techniques have exhibited remarkable importance in analytical chemistry since they were first developed in the 1980s. The application of these techniques involves efficient and, at the same time, environmentally-friendly analytical methodologies. They are also generally faster when compared with classical sample preparation techniques, requiring low solvent and sample volumes, and also allowing for automated or semi-automated procedures. This paper provides an overview of the basic principles of sample preparation techniques and the important applications and developments that have taken place in this area over the past five years. These procedures include solid-phase microextraction (SPME), stir bar sorptive extraction (SBSE), bar adsorptive microextraction (BAμE), rotating disk sorptive extraction (RDSE), micro solid-phase extraction (μ-SPE) and liquid-phase microextraction (LPME). The main variations are discussed with a focus on recent applications in the analysis of environmental water samples. Lastly, some of the trends and perspectives associated with these outstanding microextraction sample preparation approaches are highlighted.     

Determination of trace Cd and Pb in natural waters by direct single drop microextraction combined with electrothermal atomic absorption spectrometry

A new method of direct single-drop microextraction combined with electrothermal atomic absorption spectrometry (ETAAS) is presented for the determination of trace Cd and Pb with dithizone (H₂DZ) as chelating reagent. Factors influencing the microextraction efficiency and determination, such as pH, microdrop volume, stirring rate, extraction time were evaluated. Under the optimized experimental conditions, the detection limits of the method are 2 and 90 pg mL⁻¹ for Cd and Pb, and the relative standards deviations for 0.5 ng mL⁻¹ Cd and 10 ng mL⁻¹ Pb are 11 and 12.8%. After 10 min of extraction, the enrichment factors for Cd and Pb are 118 and 90, respectively. The results for the determination of Cd and Pb in tap water, spring water, river water, pond water, lake water and spiked water samples demonstrate the accuracy, recovery and applicability of the method. An environmental water certified reference material (GSBZ 50009-88) was analyzed, and the determined values are in a good agreement with the certified values. Correspondence: Bin Hu, Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China     

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.     

Determination of Endocrine Disruptors in Environmental Water by Single-Drop Microextraction and High-Performance Liquid Chromatography

Using single-drop microextraction followed by high performance liquid chromatography, an effective method for the rapid extraction for endocrine disruptors, including estrogens and alkylphenols, was developed. Factors that influenced the extraction efficiency, such as hydrogen bonding, hydrophobic property, polarity, and van der Waals forces, were evaluated in detail. The results indicated that bisphenol A and estrogens were extracted effectively by the solvents with hydrogen bond acceptors and higher polarity; alkylphenols preferred solvents that could supply strong van der Waals forces or possessed π-π stacking structures and superior hydrophobicity. The optimum extraction conditions were determined, including extraction time, pH, and salt effects. Under the optimized conditions, high extraction factors (≥147) were achieved. Limits of detection for the endocrine disruptors were between 0.33 and 0.67 µg L^?1. The method strategy is well suited for the determination of trace levels of endocrine disruptors in environmental water.