Application of surfactant assisted dispersive liquid-liquid microextraction for sample preparation of chlorophenols in water samples

A simple, rapid, and efficient method, based on surfactant assisted dispersive liquid-liquid microextraction (SA-DLLME), followed by high performance liquid chromatography (HPLC) has been developed for the extraction and determination of chlorophenols as model compounds in environmental water samples. A conventional cationic surfactant called cethyltrimethyl ammonium bromide (CTAB) was used as a disperser agent in the proposed approach. Thirty-five microliter of 1-octanol as an extraction solvent was injected rapidly into 11 mL aqueous sample containing 0.09 mmol L⁻¹ of CTAB, the mixture was then shaken for 3 min to disperse the organic phase. Having the extraction procedure been completed, the mixture was centrifuged and 20 μL of collected phase was injected into HPLC for subsequent analysis. Some parameters such as the type and volume of the extraction solvent, the type and concentration of surfactant, pH, ionic strength, shaking time, extraction temperature and centrifugation time were optimized. The preconcentration factors (PFs) in a range of 187-353 were obtained under the optimum conditions. The linear range, detection limit (S/N = 3), and precision (n = 5) were 0.2-200, 0.1 μg L⁻¹, and 4.7-6.9%, respectively. Tap water, sea water and mineral water samples were successfully analyzed for the existence of chlorophenols using the proposed method.     

Novel polyamide-based nanofibers prepared by electrospinning technique for headspace solid-phase microextraction of phenol and chlorophenols from environmental samples

A novel solid phase microextraction (SPME) fiber was fabricated by electrospinning method in which a polymeric solution was converted to nanofibers using high voltages. A thin stainless steel wire was coated by the network of polymeric nanofibers. The polymeric nanofiber coating on the wire was mechanically stable due to the fine and continuous nanofibers formation around the wire with a three dimensional structure. Polyamide (nylon 6), due to its suitable characteristics was used to prepare the unbreakable SPME nanofiber. The scanning electron microscopy (SEM) images of this new coating showed a diameter range of 100–200 nm for polyamide nanofibers with a homogeneous and porous surface structure. The extraction efficiency of new coating was investigated for headspace solid-phase microextraction (HS-SPME) of some environmentally important chlorophenols from aqueous samples followed by gas chromatography–mass spectrometry (GC–MS) analysis. Effect of different parameters influencing the extraction efficiency including extraction temperature, extraction time, ionic strength and polyamide amount were investigated and optimized. In order to improve the chromatographic behavior of phenolic compounds, all the analytes were derivatized prior to the extraction process using basic acetic anhydride. The detection limits of the method under optimized conditions were in the range of 2–10 ng L⁻¹. The relative standard deviations (RSD) (n = 3) at the concentration level of 1.7–6.7 ng mL⁻¹ were obtained between 1 and 7.4%. The calibration curves of chlorophenols showed linearity in the range of 27–1330 ng L⁻¹ for phenol and monochlorophenols and 7–1000 ng L⁻¹ for dichloro and trichlorophenols. Also, the proposed method was successfully applied to the extraction of phenol and chlorophenols from real water samples and relative recoveries were between 84 and 98% for all the selected analytes except for 2,4,6 tricholophenol which was between 72 and 74%.     

One-step extraction and derivatization liquid-phase microextraction for the determination of chlorophenols by gas chromatography–mass spectrometry

A sample pretreatment method for the determination of 18 chlorophenols (CPs) in aqueous samples by derivatization liquid-phase microextraction (LPME) was investigated using gas chromatography–mass spectrometry. Derivatization reagent was spiked into the extraction solvent to combine derivatization and extraction into one step. High sensitivity of 18 CPs derivatives could be achieved after optimization of several parameters such as extraction solvent, percentage of derivatization reagent, extraction time, pH, and ionic strength. The results from the optimal method showed that calibration ranging from 0.5 to 500 μg L⁻¹ could be achieved with the RSDs between 1.75% and 9.39%, and the limits of detection (LOD) are ranging from 0.01 to 0.12 μg L⁻¹ for the CPs. Moreover, the proposed LPME method was compared with solid-phase microextraction (SPME) coupled with on-fiber derivatization technique. The results suggested that using both methods are quite agreeable. Furthermore, the recoveries of LPME evaluated by spiked environmental samples ranged from 87.9% (3,5-DCP) to 114.7% (2,3,5,6-TeCP), and environmental water samples collected from the Pearl River were analyzed with the optimized LPME method, the concentrations of 18 CPs ranged from 0.0237 μg L⁻¹ (3,5-DCP) to 0.3623 μg L⁻¹ (2,3,6-TCP).     

Determination of the alkyl- and methoxy-phenolic content in wood extractives by micellar solid-phase microextraction and gas chromatography-mass spectrometry

This work combines the utilization of the micellar media during the extraction step and the focused microwave-assisted extraction followed by the solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) to determine the alkyl- and methoxy-phenolic content in wood extractives. The proposed environmental-friendly method is mainly characterized by short analysis times (5 min for the microwaves extraction step) and for avoiding the use of organic solvents. Different surfactants were tried for the extraction process: the cationic surfactant CTAB and the non-ionic surfactants Triton X-100 and POLE, with similar extraction efficiencies (85.5-99.7%). The overall method presents limits of detection in the ng g⁻¹ region for the alkylphenols (from 7 to 150 ng g⁻¹) and in the μg g⁻¹ region for the methoxyphenols (from 0.80 to 22.9 μg g⁻¹). The vanillin was the compound most abundant in the wood extractives studied, with concentrations up to 116.2 mg kg⁻¹.     

Stir bar sorptive extraction with in situ derivatization and thermal desorption-gas chromatography-mass spectrometry for determination of chlorophenols in water and body fluid samples

A new method, stir bar sorptive extraction (SBSE) with in situ derivatization and thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of chlorophenols, such as 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP) and pentachlorophenol (PCP), in tap water, river water and human urine samples, is described. The derivatization conditions with acetic acid anhydride and the SBSE conditions such as extraction time are investigated. Then, the stir bar is subjected to TD followed by GC-MS. The detection limits of the chlorophenols in tap water, river water and human urine samples are 1-2, 1-2, and 10-20 pg ml⁻¹ (ppt), respectively. The calibration curves for the chlorophenols are linear and have correlation coefficients higher than 0.99. The average recoveries of the chlorophenols in all the samples are higher than 95% (R.S.D. < 10%) with correction using added surrogate standards, 2,4-dichlorophenol-d₅, 2,4,6-trichlorophenol-¹³C₆, 2,3,4,6-tetrachlorophenol-¹³C₆ and pentachlorophenol-¹³C₆. This simple, accurate, sensitive and selective analytical method may be applicable to the determination of trace amounts of chlorophenols in liquid samples.     

Determination of chlorophenols in landfill leachate using headspace sampling with ionic liquid-coated solid-phase microextraction fibers combined with gas chromatography–mass spectrometry

A new microextraction technique based on ionic liquid solid-phase microextraction (IL-SPME) was developed for determination of trace chlorophenols (CPs) in landfill leachate. The synthesized ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]), was coated onto the spent fiber of SPME for extraction of trace CPs. After extraction, the absorbed analytes were desorbed and quantified using gas chromatography–mass spectrometry (GC/MS). The term of the proposed method is as ionic liquid-coated of solid-phase microextraction combined with gas chromatography–mass spectrometry (IL-SPME-GC/MS). No carryover effect was found, and every laboratory-made ionic liquids-coated-fiber could be used for extraction at least eighty times without degradation of efficiency. The chlorophenols studied were 2,4-dichlorophenol (2,4-DP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP). The best results of chlorophenols analysis were obtained with landfill leachate at pH 2, headspace extraction for 4 min, and thermal desorption with the gas chromatograph injector at 240 °C for 4 min. Linearity was observed from 0.1 to 1000 μg L⁻¹ with relative standard deviations (RSD) less than 7% and recoveries were over 87%. The limit of detection (LOD) for pentachlorophenol was 0.008 μg L⁻¹. The proposed method was tested by analyzing landfill leachate from a sewage farm. The concentrations of chlorophenols were detected to range from 1.1 to 1.4 μg L⁻¹. The results demonstrate that the IL-SPME-GC/MS method is highly effective in analyzing trace chlorophenols in landfill leachate.     

On-line trace enrichment of phenolic compounds from water using a pyrrole-based polymer as the solid-phase extraction sorbent coupled with high-performance liquid chromatography

A pyrrole-based conductive polymer was prepared and applied as new sorbent for on-line solid-phase extraction (SPE) of phenol and chlorophenols from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in non-aqueous solution. The efficiency of this polymer for extraction of phenol and chlorophenols was evaluated using 35 mg of PPy as the sorbent in an on-line SPE system coupled to reversed-phase liquid chromatography with UV detection. The mobile phase were mixture of phosphate buffer-acetonitrile and compounds were eluted by the mobile phase using a six-port switching valve. High volumes of water, up to 160 ml, could be preconcentrated without the loss of phenols, except for the more polar ones. The R.S.D. for a river water sample spiked with phenol and chlorophenols at sub-ppb level was lower than 7% (n=5) and detection limits of 15-100 and 35-150 ng l⁻¹ for tap and river water were obtained, respectively.     

Taguchi OA16 orthogonal array design for the optimization of cloud point extraction for selenium determination in environmental and biological samples by tungsten-modified tube electrothermal atomic absorption spectrometry

Orthogonal array design (OAD) was applied for the first time to optimize cloud point extraction (CPE) conditions for Se(IV) determination by electrothermal atomic absorption spectrometry (ETAAS) in environmental and biological samples. Selenium was reacted with o-phenylenediamine to form piazselenol in an acidic medium (pH 2). Using Triton X-114, as surfactant, piazselenol was quantitatively extracted into small volume (about 30 μL) of the surfactant-rich phase after centrifugation. Five relevant factors, i.e. surfactant concentration, pH, ionic strength, equilibrium time and temperature were selected and the effects of each factor were studied at four levels on the extraction efficiency of Se(IV) and optimized. The statistical analysis revealed that the most important factors contributing to the extraction efficiency are ionic strength, pH and percent of surfactant. Based on the results obtained from the analysis of variance (ANOVA), the optimum conditions for extraction were established as: pH 6; vial temperature = 50 °C; extraction time = 7 min and 0.3% (w/v) of Triton X-114. The method was permitted to obtain a detection limit of 0.09 ng mL⁻¹ and two linear calibration ranges from 0.6 to 1.0 and 1.0 to 80.0 ng mL⁻¹ Se. The precision (%RSD) of the extraction and determination for the six replicates of Se at 20 ng mL⁻¹ was better than 3.6% and the enrichment factor of 63.5 was achieved. The studied analyte was successfully extracted and determined with high efficiency using cloud point extraction method in water and biological matrices.     

Magnetic solid-phase extraction of sulfonylurea herbicides in environmental water samples by Fe3O4@dioctadecyl dimethyl ammonium chloride@silica magnetic particles

A magnetic solid phase extraction (MSPE) method coupled with high-performance liquid chromatography (HPLC) was proposed for the determination of five sulfonylurea herbicides (bensulfuron-methyl, prosulfuron, pyrazosulfuron-ethyl, chlorimuron-ethyl and triflusulfuron-methyl) in environmental water samples. The magnetic adsorbent was prepared by incorporating Fe₃O₄ nanoparticles and surfactant into a silica matrix according to a sol–gel procedure, which can provide surfactant free extracts during the eluting step to avoid chromatographic interference. The prepared adsorbent was used to extract the sulfonylurea herbicides in several kinds of water samples. The main factors affecting the extraction efficiency, including desorption conditions, extraction time, sample volume, and sample solution pH were optimized. Under the optimum conditions, good linearity was obtained within the range of 0.2–50.0 μg L⁻¹ for all analytes, with correlation coefficients ranging from 0.9993 to 0.9999. The enrichment factors were between 1200 and 1410, and the limits of detection were between 0.078 and 0.10 μg L⁻¹. The proposed method was successfully applied in the analysis of sulfonylurea herbicides in environmental samples (tap, reservoir, river, and rice field). The recoveries of the method ranged between 80.4% and 107.1%. This study reported for the first time the use of MSPE procedure in the preconcentration of sulfonylurea herbicides in environmental samples. The procedure proved to be efficient, environmentally friendly, and fast.     

Analysis of chlorophenols,bisphenol-A, 4-tert-octylphenol and 4-nonylphenols in soil by means of ultrasonic solvent extraction and stir bar sorptive extraction with in situ derivatisation

A novel method based on ultrasonic solvent extraction and stir bar sorptive extraction for the analysis of phenolic organic pollutants including chlorophenols, bisphenol-A, 4-tert-octylphenol and 4-nonylphenol in soil samples was developed. The different parameters that affect both the extraction of analytes from the soil samples, such as solvent selection, extraction time, and the partitioning from the solvent/water mix to poly(dimethylsiloxane) (PDMS) were studied. The final selected conditions consisted of the extraction of 1 g of soil with 15 mL methanol by sonication for 30 min. The methanol extract was mixed with 85 mL of Milli-Q water and extracted by means of stir bar sorptive extraction with in situ derivatisation. The stir bars were analyzed by thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). The effects of the matrix on the recovery of the various pollutants under the developed method were studied using two soils with very different physicochemical properties. Method sensitivity, linearity, repeatability, and reproducibility were also studied. Validation and accuracy of the method were conducted by analyzing two commercial certified reference materials and by comparing the analysis of real samples with the proposed method and a classical method using pressurized solvent extraction (PSE)–GC–MS. The main advantage of this method is a substantial solvent reduction. For the extraction of only 1 g of solid sample allowing limits of detection ranging from 0.2 to 1.7 μg kg⁻¹ dw. Repeatability and reproducibility variation were lower than 20% for all investigated compounds. Results of the certified reference materials and the real samples verify the high accuracy of this method.     

Species selective preconcentration and quantification of gold nanoparticles using cloud point extraction and electrothermal atomic absorption spectrometry

The determination of metallic nanoparticles in environmental samples requires sample pretreatment that ideally combines pre-concentration and species selectivity. With cloud point extraction (CPE) using the surfactant Triton X-114 we present a simple and cost effective separation technique that meets both criteria. Effective separation of ionic gold species and Au nanoparticles (Au-NPs) is achieved by using sodium thiosulphate as a complexing agent. The extraction efficiency for Au-NP ranged from 1.01 ± 0.06 (particle size 2 nm) to 0.52 ± 0.16 (particle size 150 nm). An enrichment factor of 80 and a low limit of detection of 5 ng L⁻¹ is achieved using electrothermal atomic absorption spectrometry (ET-AAS) for quantification. TEM measurements showed that the particle size is not affected by the CPE process. Natural organic matter (NOM) is tolerated up to a concentration of 10 mg L⁻¹. The precision of the method expressed as the standard deviation of 12 replicates at an Au-NP concentration of 100 ng L⁻¹ is 9.5%. A relation between particle concentration and the extraction efficiency was not observed. Spiking experiments showed a recovery higher than 91% for environmental water samples.     

Evaluation of a magnetic polysulfone microcapsule containing organic modified montmorillonite as a novel solid-phase extraction sorbent with chlorophenols as model compounds

A porous polysulfone microcapsule containing organic modified montmorillonite and magnetic nanoparticles (OMMT-Fe₃O₄@PSF) has been successfully prepared by a phase-inversion method and evaluated as a magnetic solid-phase extraction (MSPE) sorbent for clean-up and enrichment of 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) in aqueous samples. Compared with a microcapsule containing the conventional extraction sorbent C18 (C18-Fe₃O₄@PSF), OMMT-Fe₃O₄@PSF had much lower cost, a faster adsorption rate, and superior uptake amounts for the investigated analytes. The proposed microcapsule has been developed for the extraction of 4-CP and 2-CP from environmental water samples and their analysis by high-performance liquid chromatography with UV detection (HPLC-UV). Various parameters, such as pH, extraction time, the mass of sorbent, and the desorption conditions, have been evaluated and the calibration curves of the chlorophenols were linear (R² ≥ 0.9985) in the range from 1.01 to 104.5 ng mL⁻¹. The limits of detection at a signal-to-noise (S/N) ratio of 3 were 0.22 and 0.17 ng mL⁻¹ and the limits of quantification calculated at S/N = 10 were 1.52 and 1.07 ng mL⁻¹ for 2-CP and 4-CP, respectively. The recoveries of 2-CP and 4-CP from natural water and the treated wastewater samples were in the range of 84.4-115% with relative standard deviations (RSDs) lower than 7.0%. The results have demonstrated the suitability of the MSPE approach for the analysis of trace chlorophenols in aqueous samples.     

Carboxyl modified multi-walled carbon nanotubes as solid-phase extraction adsorbents combined with high-performance liquid chromatography for analysis of linear alkylbenzene sulfonates

Recently, multi-wall carbon nanotubes (MWCNTs) as adsorbents of solid-phase extraction are attractive because they can be used for enrichment of organic compounds and metal ions at trace levels. In this study, we use the carboxyl modified multi-wall carbon nanotubes (CMMWCNTs) as adsorbents of solid-phase extraction for extraction of linear alkylbenzene sulfonates (LAS), which are widely used anion surfactant with different homologues, and detected by HPLC-UV. The effect of eluent and its volume, sample pH and flow rate, sample volume and the ultrasonic time of sample, the content of the electrolyte (NaCl) were investigated and optimized. The detection limit for LAS homologues was 0.02-0.03 μg L⁻¹ with R.S.D. (n = 6) ranging from 2.04 to 10.03%. The recoveries of LAS homologues in the spiked environmental water samples ranged from 84.8 to 106.1%. The proposed method has been applied successfully to the analysis of LAS in aqueous environmental samples, which demonstrates that CMMWCNTs-based solid-phase extraction is a precision and convenient enrichment method and can be used for analysis of LAS homologues in water samples.     

A green method using micellar system for determination of sulfonamides in soil

A green and simple method was developed for determination of sulfonamides (SAs) in soil samples. The procedure was based on the microwave-assisted extraction (MAE) of SAs from soil using non-ionic surfactant Triton X-114 as the extraction medium. Then sodium chloride was added into the MAE extract and the mixture was equilibrated for some time at high temperature. The analytes in the surfactant-rich phase were concentrated with the help of centrifugation and directly analyzed by high performance liquid chromatography with UV detection. None of potentially hazardous organic solvents was used in the whole sample preparation procedure. The significant variables for the performance of extraction and concentration were studied. The limits of detection of SAs obtained are in the range of 3.2-5.7 ng g⁻¹. The relative standard deviations of intra- and inter-day tests ranging from 3.5% to 7.7% and from 4.6% to 9.5% are obtained, respectively. This method was applied to the determination of SAs in some soil samples with different characteristics. The SAs recoveries obtained at fortified level of 100 ng g⁻¹ for these samples are in the range of 81.2-93.7%. The effect of ageing time of spiked soil samples on the SAs recoveries was examined by the proposed method and a method reported in the literature. The recoveries of SAs decreased when the ageing time changed from 1 day to 4 weeks.     

Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamate pesticides in water samples by high performance liquid chromatography

A novel ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) coupled with high performance liquid chromatography-diode array detection has been developed for the extraction and determination of six carbamate pesticides (metolcarb, carbofuran, carbaryl, pirimicarb, isoprocarb and diethofencarb) in water samples. In the UASEME technique, Tween 20 was used as emulsifier, and chlorobenzene and chloroform were used as dual extraction solvent without using any organic dispersive solvent that is normally required in the previously described common dispersive liquid–liquid microextraction method. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 170 and 246. The limits of detection of the method were 0.1–0.3 ng mL⁻¹ and the limits of quantification were between 0.3 and 0.9 ng mL⁻¹, depending on the compounds. The linearity of the method was obtained in the range of 0.3–200 ng mL⁻¹ for metolcarb, carbaryl, pirimicarb, and diethofencarb, 0.6–200 ng mL⁻¹ for carbofuran, and 0.9–200 ng mL⁻¹ for isoprocarb, with the correlation coefficients (r) ranging from 0.9982 to 0.9998. The relative standard deviations varied from 3.2 to 4.8% (n = 5). The recoveries of the method for the six carbamates from water samples at spiking levels of 1.0, 10.0, 50.0 and 100.0 ng mL⁻¹ were ranged from 81.0 to 97.5%. The proposed UASEME technique has demonstrated to be simple, practical and environmentally friendly for the determination of carbamates residues in river, reservoir and well water samples.     

Evaluation of carbon nanocones/disks as sorbent material for solid-phase extraction

The potential of carbon nanocones/disks as sorbent material in solid-phase extraction (SPE) procedures has been evaluated. For this aim, a model analytical problem, the determination of chlorophenols in water samples, was selected. An accurately weighed amount of 20 mg of purified carbon nanocones/disks was packed in 3 mL commercial SPE cartridges. Once conditioned, up to 8 mL of water samples can be preconcentrated without analyte losses. The chlorophenols were eluted by using 200 μL of hexane. Aliquots of 2 μL of the organic extract were injected in the gas chromatograph–mass spectrometer for separation and quantification. The purification of the commercial nanocones/disks to reduce the presence of amorphous carbon has been successfully achieved by heating the carbon nanocones/disks at 450 °C for 20 min. Detection limits of chlorophenols were in the range 0.3–8 ng mL⁻¹ by using 2 mL of sample. Moreover, excellent average recovery values (98.8–100.9%) have been obtained after the analysis of water samples from different nature. Finally, the performance of the carbon nanocones/disks as sorbent material has been compared with that of multiwalled carbon nanotubes, providing the former better results under the experimental conditions assayed.     

Solid-phase extraction combined with headspace single-drop microextraction of chlorophenols as their methyl ethers and analysis by high-performance liquid chromatography-diode array detection

Solid-phase extraction (SPE) of phenol and chlorophenols, their derivatization to methyl ethers, headspace single-drop microextraction (HS-SDME) of methyl ethers using 1-butanol as extraction solvent, and direct transfer of the drop into the injector for high performance liquid chromatography with diode array detection (HPLC-DAD) have been reported. A flanged-end polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, placed at the tip of the syringe needle, allowed the use of 10 μL solvent drop for extraction. The procedure has been optimized for variables involved in SPE and HS-SDME. A rectilinear relationship was obtained between the amount of chlorophenols and peak area ratio of their methyl ethers/internal standard (4-methoxyacetophenone) in the range 0.01-10 mg L⁻¹, correlation coefficient in the range 0.9956-0.9996, and limit of detection in the range 1.5-3.9 μg L⁻¹ when HS-SDME alone was used for sample preparation. When using coupled SPE and HS-SDME, the linear range obtained was 0.1-500 μg L⁻¹, correlation coefficient in the range 0.9974-0.9998, and the limit of detection in the range 0.04-0.08 μg L⁻¹. Spiked real samples have been analyzed with adequate accuracy, and application of the method has been demonstrated for the analysis of chlorophenols formed upon bamboo pulp bleaching.     

Cold column trapping-cloud point extraction coupled to high performance liquid chromatography for preconcentration and determination of curcumin in human urine

A cold column trapping-cloud point extraction (CCT-CPE) method coupled to high performance liquid chromatography (HPLC) was developed for preconcentration and determination of curcumin in human urine. A nonionic surfactant, Triton X-100, was used as the extraction medium. In the proposed method, a low surfactant concentration of 0.4% v/v and a short heating time of only 2 min at 70 °C were sufficient for quantitative extraction of the analyte. For the separation of the extraction phase, the resulted cloudy solution was passed through a packed trapping column that was cooled to 0 °C. The temperature of the CCT column was then increased to 25 °C and the surfactant rich phase was desorbed with 400 μL ethanol to be directly injected into HPLC for the analysis. The effects of different variables such as pH, surfactant concentration, cloud point temperature and time were investigated and optimum conditions were established by a central composite design (response surface) method. A limit of detection of 0.066 mg L⁻¹ curcumin and a linear range of 0.22–100 mg L⁻¹ with a determination coefficient of 0.9998 were obtained for the method. The average recovery and relative standard deviation for six replicated analysis were 101.0% and 2.77%, respectively. The CCT-CPE technique was faster than a conventional CPE method requiring a lower concentration of the surfactant and lower temperatures with no need for the centrifugation. The proposed method was successfully applied to the analysis of curcumin in human urine samples.     

Determination of osthole in rat plasma by high-performance liquid chromatograph using cloud-point extraction

A new straightforward method based on cloud-point extraction (CPE) was developed to determine osthole in rat plasma by reversed phase high-performance liquid chromatography with ultraviolet detection using a photodiode array detector. The non-ionic surfactant Triton X-114 was chosen as the extract solvent. Variable parameters affecting the CPE efficiency were evaluated and optimized. A Zorbax SB-C₁₈ column was used for elution separation at 25 °C with detection wavelength at 322 nm. Under the optimum conditions, the method was shown to be reproducible and reliable with intra-day precision below 7.62%, inter-day precision below 6.37%, and accuracy within ±5.02% and mean extraction recovery more than 90.4%, which were all calculated using a range of spiked samples at three concentrations of 0.5, 5.0 and 15.0 μg mL⁻¹ for osthole in plasma. The calibration curve for the analyte was linear in the range from 0.1 to 20 μg mL⁻¹ with the correlation coefficients greater than 0.9981. Limit of detection (S/N = 3) was less than 0.03 μg mL⁻¹and limit of quantification (S/N = 10) was less than 0.1 μg mL⁻¹. After strict validation, the method was successfully applied to the pharmacokinetic study of osthole in rats after oral and intravenous administration, respectively.     

Solid phase extractive preconcentration coupled to gas chromatography-atomic emission detection for the determination of chlorophenols in water samples

Solid-phase extraction (SPE) followed by derivatization and gas chromatography-atomic emission detection (GC-AED) was evaluated for the determination of five chlorophenols (CPs) in water samples. The derivatization was based on the esterification of phenolic compounds with ferrocenecarboxylic acid. The determination of the derivatized phenols was performed by GC-AED in the iron selective detection mode at 302 nm. The described method was tested on spiked water samples.The overall method gave detection limits of 1.6-3.7 ng L⁻¹ and recoveries of 90.9-104.5% for the examined mono- to trichlorophenols in 10 mL water samples. The CPs extracted from a 10 mL water sample with SPE were concentrated into 100 μL of organic solvent, a preconcentration factor of 100. The method was applied to lake and tap water samples, and CP contents between 6 and 51 ng L⁻¹ in lake water and between below the detection limit and 8 ng L⁻¹ in tap water were found for different CPs. The method is quick, simple and gives excellent recoveries, limits of detection and standard deviations.