Microwave assisted micellar extraction coupled with solid phase microextraction for the determination of organochlorine pesticides in soil samples

Microwave assisted micellar extraction (MAME) coupled with solid phase microextraction (SPME) and HPLC-UV determination have been used for the determination of five organochlorine pesticides from agricultural soil samples. A non-ionic surfactant, Polyoxyethlylene 10 Lauryl Ether was used, and the different variables for the optimization of MAME and SPME procedures were studied. This method was applied successfully to the determination of these pesticides in several kinds of agricultural soil samples with different characteristics. Most of the compounds studied can be recovered in good yields with R.S.D. lower than 9% and detection limit ranged between 56-96 ng g⁻¹ for the pesticides studied.     

Recent trends in the use of organized molecular systems combined with chromatographic techniques in environmental analysis

The establishment of new analytical methods which improve quality and sensitivity in the determination of environmental pollutants in liquid and solid samples is demanded. The use of micellar systems have become an advantageous tool for the extraction of pollutant compounds, due to their easy handling, biodegradability, and the one-step procedure, and they are compatible with the hydroalcoholic mobile phases used in HPLC. The focus of this review is to present recently developed methods and the main trends in the use of micellar media combined with solid-phase microextraction and solid-phase extraction in the chromatographic analysis of organic compounds in different types of environmental matrix, including water, sediments, and biological samples. Selected samples illustrate the benefits of these systems in the whole of analytical process. The advantages of micellar media over conventional extractants are reduction of solvent usage, low cost, easy handling, and non-toxic procedure.     

Chromatographic determination of caffeine in pharmaceutical formulations using micellar mobile phases

Summary An HPLC procedure is described for the determination of caffeine in pharmaceutical preparations. A Spherisorb octadecylsilane ODS-2 C₁₈ analytical column and spectrophotometric detection at 273 nm were used. The chromatographic behaviour of caffeine with different micellar eluents containing sodium dodecyl sulphate (SDS) is described. The determination of caffeine in pharmaceutical preparations was performed by use of a mobile phase containing 0.05 M sodium dodecylsulphate (SDS) and 1.5% propanol at pH7. At a 6.0 g mL^–1 concentration level the peak area and peak height repeatability were 2.6 and 2.4%, respectively. The application of the proposed method to the analysis of five pharmaceutical formulations, using peak heights as the dependent variable, gave recoveries between 85 and 104% of the values declared by the manufacturers. The proposed procedure for the determination of caffeine is rapid (15 min per sample), reliable and free from interferences.     

Development of a micellar electrokinetic capillary chromatography method for the determination of four naphthalenediols in cosmetics and a comparison with a HPLC method

A micellar electrokinetic capillary chromatography (MEKC) method with ultraviolet visible (UV) detection was used for the determination of 1,7-naphthalenediol, 2,3-naphthalenediol, 1,5-naphthalenediol, and 2,7-naphthalenediol in cosmetics. The current method for their determination in various cosmetics is high-performance liquid chromatography (HPLC). Separation conditions affecting the MEKC method were optimized as 20 mM Na₂B₄O₇–50mM SDS, pH 9.8, with 22 kV applied voltage and UV detection at 230 nm. Under optimal conditions, electrophoretic analysis was completed in less than 6 min, with limit of detection (LOD) of 0.070–0.19 μg/mL and limit of quantitation (LOQ) of 0.23–0.63 μg/mL. A good linear relationship (r² > 0.99) was obtained at the range of 0.75–20 μg/mL. Recoveries for the four naphthalenediols in lotion, loose powder, and sun cream are between 91.2–107.2% with relative standard deviation (RSD) less than 4.04%. The method has been successfully applied to the determination of the four naphthalenediols in different kinds of cosmetics. A comparison with HPLC-UV method was also carried out according to the National Standards of the People's Republic of China. The results obtained by MEKC and HPLC methods are comparable, but the proposed MEKC method can help us obtain a much shorter detection time and low cost.     

Uptake monitoring of anilines and phenols using modified zeolites

Uptake monitoring of a group of environmentally important phenolic and aniline compounds including aniline, phenol, 4-methylaniline, 4-aminophenol, 2-aminophenol, 4-nitrophenol, 2-nitrophenol and 2-methyl-4-nitrophenol was carried out using micellar electrokinetic capillary chromatography. For the removal of tested pollutants, the natural zeolites natrolite and clinoptilolite were examined in which the latter showed better uptakes ranging from 45 to 64% of pollutants from aqueous solution in 4 h. Modification of zeolites with cyclodextrins (CDs), especially, α-CD, considerably improves the uptake efficiency to 65-74% for clinoptilolite. The effects of equilibrium time, type and concentration of CDs were also investigated. The versatility of micellar electrokinetic capillary chromatography was shown for this type of study owing to its speed, resolution ability, and simplicity.     

Application of microwave-assisted micellar extraction combined with solid-phase microextraction and high-performance liquid chromatography with UV detection for the determination of organochlorine pesticides in different mud samples

Abstract

A sequential injection analysis method for the simultaneous spectrophotometric determination of phosphate and silicate has been developed. The method is based on the different reaction rates of the heteropolymolybdate formation reactions. Concentrations within the range 0.026—0.485 mmol P l^?1 and 0.125—2.848 mmol Si l^?1 have been determined at a frequency of 30 samples per hour. An R.S.D. of 2.1% was obtained for 0.162 mmol P l^?1 and of 1.1% for 1.424 mmol Si l^?1. The method was found to be suitable for the determination of phosphate and silicate in wastewater.     

Efficient extraction of PAHs in aqueous organised media assisted by focused microwaves

Summary A novel method for the extraction into an aqueous medium of PAHs in soil is described, where sodium dodecyl sulphate (SDS) is used as micelle former. After optimisation of this step using a multivariate approach, recoveries of the target analytes from spiked soil ranging between 98.3%–99.7% were obtained when the samples were subjected to extraction with 25 mL of an aqueous SDS solution (2.9 10⁻² mol L⁻¹) while irradiated with focused microwaves at 240 W for 40 min. The overall method involving determination of the extracted compounds consists of three steps: 1) extraction of the analytes into the aqueous micellar medium assisted by focused microwaves; 2) trapping of the analytes on a C₁₈ cartridge for clean up and preconcentration and; 3) HPLC separation with fluorimetric detection. The method was validated using the certified reference material CRM 524 and the results found were in agreement with the certified values.     

Ionic liquid-based microwave-assisted extraction of rutin from Chinese medicinal plants

An ionic liquid-based microwave-assisted extraction (ILMAE) method has been developed for the effective extraction of rutin from Chinese medicinal plants including Saururus chinensis (Lour.) Bail. (S. chinensis) and Flos Sophorae. A series of 1-butyl-3-methylimidazolium ionic liquids with different anions were investigated. The results indicated that the characteristics of anions have remarkable effects on the extraction efficiency of rutin and among the investigated ionic liquids, 1-butyl-3-methylimidazolium bromide ([bmim]Br) aqueous solution was the best. In addition, the ILMAE procedures for the two kinds of medicinal herbs were also optimized by means of a series of single factor experiments and an L₉ (3⁴) orthogonal design. Compared with the optimal ionic liquid-based heating extraction (ILHE), marinated extraction (ILME), ultrasonic-assisted extraction (ILUAE), the optimized approach of ILMAE gained higher extraction efficiency which is 4.879 mg/g in S. chinensis with RSD 1.33% and 171.82 mg/g in Flos Sophorae with RSD 1.47% within the shortest extraction time. Reversed phase high performance liquid chromatography (RP-HPLC) with ultraviolet detection was employed for the analysis of rutin in Chinese medicinal plants. Under the optimum conditions, the average recoveries of rutin from S. chinensis and Flos Sophorae were 101.23% and 99.62% with RSD lower than 3%, respectively. The developed approach is linear at concentrations from 42 to 252 mg L⁻¹ of rutin solution, with the regression coefficient (r) at 0.99917. Moreover, the extraction mechanism of ILMAE and the microstructures and chemical structures of the two researched samples before and after extraction were also investigated. With the help of LC-MS, it was future demonstrated that the two researched herbs do contain active ingredient of rutin and ionic liquids would not influence the structure of rutin.     

用快速分离柱高效液相色谱法测定烟草中的几种酚

研究了用快速分离柱高效液相色谱法测定烟草样品中的苯酚、苯二酚和甲基苯酚. 烟草样品中的酚经水蒸汽蒸馏分离后用Waters Sep-Pak-C18固相萃取小柱富集, 以ZORBAX Stable Bound (4.6 mm i.d.×20 mm, 1.8 μm) 快速分离柱为固定相, 0.05 mol/L KH2PO4缓冲溶液-甲醇梯度为流动相, 几种主要酚在2.0 min 内可达到基线分离;该方法的相对标准偏差为2.1%～3.6%, 标准加入的回收率为88%～97%, 已用于几种烟草样品测定.     

Surfactant-assisted pressurized liquid extraction for determination of flavonoids from Costus speciosus by micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC), a mode of capillary electrophoresis (CE), is considered an efficient analytical technique allowing for the reduction of organic solvent consumption during the experimental procedure. However, during sample preparation of natural products, the usage of large amount of organic solvent is generally unavoidable. In this article, therefore, a fast, simple, efficient, highly automatic and organic solvent-free sample preparation method, namely surfactant-assisted pressurized liquid extraction (PLE), was developed for the extraction of flavonoids in Costus speciosus flowers before MEKC analysis. The various experimental parameters such as the type and concentration of surfactant, and extraction time were evaluated systematically. Under the optimized conditions, the extraction efficiencies of surfactant-assisted PLE methods were comparable with Soxhlet extraction using organic solvent. The combination of surfactant-assisted PLE and MEKC was shown to be a green, rapid and effective approach for extraction and analysis of flavonoids in C. speciosus flowers.     

Use of cloud point extraction methodology for the determination of PAHs priority pollutants in water samples by high-performance liquid chromatography with fluorescence detection and wavelength programming

The cloud point extraction methodology has been used to develop a new procedure for the preconcentration of polycyclic aromatic hydrocarbons in water samples (bottled and network supply). Triton X-114 was used as extractant agent. The procedure, consisting of three steps (preconcentration into the surfactant, clean-up and concentration of the eluate), allows good detection limits to be reached (from nanograms per liter to even sub-nanograms per liter in some cases). Determination was carried out by HPLC, with fluorimetric detection and wavelength programming.     

A cost effective,sensitive, and environmentally friendly sample preparation method for determination of polycyclic aromatic hydrocarbons in solid samples

A simple, cost effective, and yet sensitive sample preparation technique was investigated for determining Polycyclic Aromatic Hydrocarbons (PAHs) in solid samples. The method comprises ultrasonic extraction, Stir Bar Sorptive Extraction (SBSE), and thermal desorption–gas chromatography–mass spectrometry to increase analytical capacity in laboratories. This method required no clean-up, satisfied PAHs recovery, and significantly advances cost performance over conventional extraction methods, such as Soxhlet and Microwave Assisted Extraction (MAE). This study evaluated three operational parameters for ultrasonic extraction: solvent composition, extraction time, and sample load. A standard material, SRM 1649 a (urban dust), was used as the solid sample matrix, and 12 priority PAHs on the US Environmental Protection Agency (US EPA) list were analyzed. Combination of non-polar and polar solvents ameliorated extraction efficiency. Acetone/hexane mixtures of 2:3 and 1:1 (v/v) gave the most satisfactory results: recoveries ranged from 63.3% to 122%. Single composition solvents (methanol, hexane, and dichloromethane) showed fewer recoveries. Comparing 20 min with 60 min sonication, longer sonication diminished extraction efficiencies in general. Furthermore, sample load became a critical factor in certain solvent systems, particularly MeOH. MAE was also compared to the ultrasonic extraction, and results determined that the 20-min ultrasonic extraction using acetone/hexane (2:3, v/v) was as potent as MAE. The SBSE method using 20 mL of 30% alcohol-fortified solution rendered a limit of detection ranging from 1.7 to 32 ng L⁻¹ and a limit of quantitation ranging from 5.8 to 110 ng L⁻¹ for the 16 US EPA PAHs.     

SPME and SPE comparative study for coupling with microwave-assisted micellar extraction in the analysis of organochlorine pesticides residues in seaweed samples

Solid-phase microextraction (SPME) and solid-phase extraction (SPE) procedures were coupling with microwave-assisted micellar extraction for organochlorine pesticides residues determination in seaweed samples. They were optimized, compared and discussed.Preliminary experiments were performed in order to study experimental conditions for the extraction of pesticides from spiked seaweed samples with microwave-assisted micellar extraction (MAME) using a non-ionic surfactant (Polyoxyethylene 10 Lauryl Ether). After that, SPME and SPE were used to clean-up and preconcentrate MAME extract prior the analysis by liquid chromatography with photodiode array (PDA) detection.Excellent results were obtained for both procedures. Average pesticide recoveries between 80.5 and 104.3% for MAME-SPME and between 73.9 and 111.5% for MAME-SPE were obtained. Relative standard deviations (RSDs) were lower than 10.3% and 5.3% respectively for all recoveries tested, and LOD between 138–348 ng g^− 1 for MAME-SPME and 2–38 ng g^− 1 for MAME-SPE were obtained. The method was validated using Soxhlet extraction procedure.Both methods were applied to analyse target organochlorine pesticides in several seaweed samples and results were compared. These results show the great possibilities of combining MAME-SPE-HPLC-UV for the analysis of seaweed samples, improving the selectivity and sensitivity in the determination of organochlorine pesticides analysis for this kind of samples.     

Comparative study of robustness between micellar electrokinetic capillary chromatography and high-performance liquid chromatography using one-variable-at-a-time and a new multi-variable-at-a-time approach

Micellar electrokinetic capillary chromatography and reverse-phase liquid chromatography methods were developed in order to perform robustness testing to determine the caffeine content in beverages. Both methods were fully validated and two different robustness approaches were applied. One-variable-at-a-time (OVAT) approach at eleven levels (0; ±1; ±2; ±3; ±4; ±5 units) was carried out and compared with multi-variable-at-a-time (MVAT) approach at three levels (±1 unit per investigated parameter). Four analysts in two laboratories on two capillary electrophoresis and two RPLC equipments have tested the samples. Robustness was statistically analyzed using peak area, migration or retention time, symmetry, and resolution of caffeine and sulfacetamide as internal standard, and presented as R.S.D. values. The RPLC method was found to be more sensitive than the MEKC method. Both methods showed acceptable robustness level for OVAT approach, whilst MEKC method was more robust when the determination of real samples coming from different beverages was based on the MVAT approach.     

A micellar liquid chromatographic method for quality control of pharmaceutical preparations containing tricyclic antidepressants

Summary Micellar liquid chromatography methods for quality control of pharmaceutical preparations (capsules, pills, tablets, injections) containing the tricyclic antidepressants amineptine, amitriptiline, clomipramine, doxepin, imipramine, melitracen and nortriptyline alone or together with other CNS drugs like diazepam, medazepam and perphenazine are described. The methods using micellar solutions of cetyltrimethylammonium bromide as mobile phases and UV detection are rapid and reproducible. Due to the versatility of interactions in micellar liquid chromatography, it is possible determine highly hydrophobic compounds such as TCAs in a short time using mobile phases containing low organic solvent concentrations and usual flow rates, in contrast with the RP-HPLC methods proposed for these compounds. Samples preparation only requires solution and adequate dilution with the mobile phase before injection into the chromatographic system.     

Development of pressurized liquid extraction and cleanup procedures for determination of organochlorine pesticides in soils

The scope of this work is the development of a rapid, reliable and sensitive method for the analysis of organochlorine pesticides from soils by pressurized liquid extraction (PLE). The effect of four parameters (temperature, pressure, static time and cell volume) on the extraction efficiency was studied. The great extracting power of the PLE causes the extraction of numerous interfering substances, so a more efficient purification of this extract was necessary. In this work several sorbents have also been assayed to carry out the purification of soil samples: Florisil, silica, alumina, carbon, as well as combinations of them. Finally, the proposed analytical method was validated using a certified reference soil material (CRM804-050) and the results were compared with those obtained by other extraction techniques (Soxhlet and microwave-assisted extraction).     

Stability-indicating micellar liquid chromatography method for three novel derivatives of zidovudine in aqueous and simulated gastric and intestinal fluids matrices

This work studies the stability of three new anti-HIV agents which were obtained by the association of zidovudine (AZT) with different amino acids, such as leucine (AZT-Leu) and valine (AZT-Val), and one with an acid group (AZT-Ac). Before commercialisation, their stability in different matrices - simulated gastric fluid (SGF, pH 1.2) and simulated intestinal fluid (SIF, pH 6.8), both as the USP 32 Guideline indicates, and buffers (pH 1.2 and 6.8) - must be studied. To this end, a new stability-indicating micellar liquid chromatography (MLC) method has been optimised and validated. Measurements were based on the disappearance of reagents and the appearance of the only degradation product (AZT). This optimised and validated method used a C18 column and a mobile phase containing 0.05 M sodium dodecyl sulphate-1% (v/v)1-butanol-0.01 M NaH(2)PO(4) (pH 3.0) at 30°C, and a flow rate of 1 mL min(-1). Under these conditions, retention times were 1.4, 3.6, 6.3 and 9.5 min for AZT-Ac, AZT, AZT-Val and AZT-Leu, respectively. Calibrations better than 0.9995, intra- and inter-day precisions below 1.08% and good recoveries (94.47-116.52%) and robustness (RSD less that 1.08%) were obtained and were adequate to analyse the four compounds. Finally, this MLC method was applied to achieve stability studies which resulted in the evidence that all the compounds followed a pseudo-first-order kinetics, and in the determination of their kinetic constants and half-life time. A reference method, applied in the same studies, validated the MLC method reported herein.     

Chemometric approach in optimization of micellar liquid chromatographic separation of some halogenated phenols

Simultaneous optimization of separation quality and analysis time of the micellar liquid chromatography of nine chlorophenol isomers was investigated. The effect on retention of three experimental parameters was studied using multivariate analysis. The factors studied were the concentration of sodium dodecyl sulfate, propanol content and pH of the mobile phase. The experiments were performed according to the face-centred cube central composite design and the inverse form of the experimental retention times for analytes were fitted to the polynomial models. The results of the analysis of variance showed that the models obtained explain greater than 99% of the variance observed in the chromatograms. Good predictive ability of the models was verified as high values of the statistics R² and F were obtained for the linear relationship between predicted cross-validated and experimental values of the dependent variable. The study showed that the use of Pareto-optimality method, an approach from multi-criteria decision-making, allows the selection of the best possible combinations of separation and analysis time in micellar liquid chromatography of chlorophenols.     

胶束液相色谱法直接注射同时测定人血清中利凡诺和米非司酮

建立了一个简单、快速的胶束液相色谱方法,直接注射样品,同时测定人血清中利凡诺和米非司酮。分离于30℃反相C18柱上进行,流动相:含75 mmol/L的十二烷基硫酸钠和体积分数9%正丁醇的混合溶液(pH4.0),流速为1.2 mL/min。以苯为内标物。采用多波长模式检测,利凡诺、米非司酮、苯的检测波长分别为272、305、256 nm。直接注射的人血清样品体积为100μL。结果表明,利凡诺、米非司酮的校准曲线分别在20~1000、50~1000 ng/mL浓度范围内呈线性,检测限分别为4.9和13.8 ng/mL,精密度和准确度良好。该方法可直接注射样品同时测定人血清中两种药物,应用于评估同时使用两种药物的妇女的血药水平。     

Optimisation of stir bar sorptive extraction for the analysis of volatile phenols in wines

An easy, fast and reliable analytical method is proposed for the determination of the concentration of volatile phenols (ethyl- and vinylphenols) in wines. The novel stir bar sorptive extraction (SBSE) technique is employed, following a simple and fast procedure that allows 15 samples to be extracted simultaneously using very small sample volume. Extracts are desorbed in a thermodesorption system (TDS) coupled on-line to a gas chromatograph-mass spectrometry system. The SBSE offers better recovery and linear regression coefficient (r2) for the four volatile phenols than solid-phase extraction (SPE). The mass spectrometric detection in selected ion monitoring mode contributes to the lower detection limit and good sensibility obtained with this method.