Carbon molecular sieve based micro‐matrix‐solid‐phase dispersion for the extraction of polyphenols in pomegranate peel by UHPLC‐Q‐TOF/MS

A rapid, simple, and efficient sample extraction method based on micro‐matrix‐solid‐phase dispersion (micro‐MSPD) was applied to the extraction of polyphenols from pomegranate peel. Five target analytes were determined by ultra‐HPLC coupled with Q‐TOF/MS. Carbon molecular sieve (CMS) was firstly used as dispersant to improve extraction efficiency in micro‐MSPD. The major micro‐MSPD parameters, such as type of dispersant, amount of dispersant, grinding time, and the type and the volume of elution solvents, were studied and optimized. Under optimized conditions, 26 mg of pomegranate peel was dispersed with 32.5 mg of CMS, the grinding time was selected as 90 s, the dispersed sample was eluted with 100 μL of methanol. Results showed that the proposed method was of good linearity for concentrations of analytes against their peak areas (coefficient of determination r² > 0.990), the LOD was as low as 3.2 ng/mL, and the spiking recoveries were between 88.1 and 106%. Satisfactory results were obtained for the extraction of gallic acid, punicalagin A, punicalagin B, catechin, and ellagic acid from pomegranate peel sample, which demonstrated nice reliability and high sensitivity of this approach.     

Development of a matrix solid-phase dispersion method for the determination of polycyclic aromatic hydrocarbons in sewage sludge samples

A new, single-step extraction and purification method based on matrix solid-phase dispersion (MSPD) was developed to determine 17 polycyclic aromatic hydrocarbons (PAHs) in sewage sludge samples. The MSPD method consists of sample homogenisation, exhaustive extraction and clean-up by a single process. The different operational parameters of the method, such as the type of dispersant, type and amount of additives, clean-up co-sorbent and extractive solvent were evaluated. Reversed-phase (C18) and polymeric (Oasis HLB and Oasis MAX) materials, as well as normal phase sorbents (Florisil, silica, neutral alumina) and an inert support (sand) were tested to assess the sorbents effect on the yield and selectivity of the MSPD process. Analysis of extracts was performed by high performance liquid chromatography (HPLC) coupled with fluorescence detection.Quantification limits obtained for all of these considered compounds (between 0.0001 and 0.005 μg g⁻¹ dry mass) were well below of the limits recommended in the EU. The extraction yields for the different compounds obtained by MSPD ranged from 76.3% to 103.6%. On the other hand, the extraction efficiency of the optimised method is compared with that achieved by microwave-assisted extraction and the method was applied to the analysis of real sewage sludge samples. A certified reference material (sewage sludge (BCR 088)) and a reference material (sewage sludge (RTC-CNS312-04)) were used to validate the proposed method.     

Fast and selective extraction of chloramphenicol from soil by matrix solid‐phase dispersion using molecularly imprinted polymer as dispersant

The molecularly imprinted polymer (MIP) was synthesized and used as dispersant of matrix solid‐phase dispersion (MSPD) for the extraction of chloramphenicol (CAP) in soil samples. The satisfactory recovery of CAP was obtained by the optimized extraction conditions: 1:2 as the ratio of sample to MIPs; 5 min as the dispersion time; 30% aqueous methanol as washing solvent and methanol as elution solvent. The CAP extracted from soil was determined by LC‐MS/MS. The slight ion suppression phenomenon was observed for the CAP when the sample was cleaned up by MSPD with MIP as dispersant, when compared with C18 as MSPD dispersant, which caused significant ion suppression. LOD of CAP is 4.1 ng/g. RSDs of intra‐ and inter‐day tests ranging from 3.1 to 6.2% and from 3.9 to 8.3% are obtained. At all three fortified levels (20, 100 and 500 ng/g), recoveries of CAP are in the range of 86.9–92.6%. The effect of ageing time of spiked soil sample on the CAP recovery was examined. The CAP recovery decreased from 91.0 to 36.9% when the ageing time changed from 1 day to 4 wk.     

Miniaturized matrix solid‐phase dispersion combined with ultrasound‐assisted dispersive liquid–liquid microextraction for the determination of three pyrethroids in soil

A simple and miniaturized pretreatment procedure combining matrix solid‐phase dispersion (MSPD) with ultrasound‐assisted dispersive liquid–liquid microextraction (UA‐DLLME) technique was proposed in first time for simultaneous determination of three pyrethroids (fenpropathrin, cyhalothrin and fenvalerate) in soils. The solid samples were directly extracted using MSPD procedure, and the eluent of MSPD was used as the dispersive solvent of the followed DLLME procedure for further purification and enrichment of the analytes before GC‐ECD analysis. Good linear relationships were obtained for all the analytes in a range of 5.0–500.0 ng/g with LOQs (S/N=10) ranged from 1.51 to 3.77 ng/g. Average recoveries at three spiked levels were in a range of 83.6–98.5% with RSD≤7.3%. The present method combined the advantages of MSPD and DLLME, and was successfully applied for the determination of three pyrethroids in soil samples.     

Matrix Solid-Phase Dispersion Extraction and UPLC Determination of Sudan Dyes in Chili Powder

A new method involving matrix solid-phase dispersion (MSPD) extraction and UPLC in conjunction with photodiode array detection was developed for the rapid and simple determination of Sudan dyes in chili powder. Separation of Sudan I, Sudan II, Sudan III, and Sudan IV was achieved within 2 min on the 1.7 μm Acquity UPLC BEH C18 column by using gradient elution with a mobile phase consisting of acetonitrile–water at a flow rate of 0.5 mL min⁻¹. Optimization of MSPD extraction parameters, such as type of solid sorbent and elution solvent were carried out. Optimal conditions selected for MSPD extraction were 0.25 g of sample, 0.5 g of silica gel as solid sorbent, and 7 mL of acetonitrile–methanol (9:1, v/v) as eluting solvent. Limits of detection ranged between 0.25 and 0.30 mg kg⁻¹ depending on the dye involved. All analytes provided average recoveries from spiked (at 1, 1.5, and 2 mg kg⁻¹) chili powder samples ranging from 81 to 106%. The method was applied to the analysis of chili powder samples obtained from different countries.

     

Use of volatile organic solvents in headspace liquid‐phase microextraction by direct cooling of the organic drop using a simple cooling capsule

A low‐cost and simple cooling‐assisted headspace liquid‐phase microextraction device for the extraction and determination of 2,6,6‐trimethyl‐1,3 cyclohexadiene‐1‐carboxaldehyde (safranal) in Saffron samples, using volatile organic solvents, was fabricated and evaluated. The main part of the cooling‐assisted headspace liquid‐phase microextraction system was a cooling capsule, with a Teflon microcup to hold the extracting organic solvent, which is able to directly cool down the extraction phase while the sample matrix is simultaneously heated. Different experimental factors such as type of organic extraction solvent, sample temperature, extraction solvent temperature, and extraction time were optimized. The optimal conditions were obtained as: extraction solvent, methanol (10 μL); extraction temperature, 60°C; extraction solvent temperature, 0°C; and extraction time, 20 min. Good linearity of the calibration curve (R² = 0.995) was obtained in the concentration range of 0.01–50.0 μg/mL. The limit of detection was 0.001 μg/mL. The relative standard deviation for 1.0 μg/mL of safranal was 10.7% (n = 6). The proposed cooling‐assisted headspace liquid‐phase microextraction device was coupled (off‐line) to high‐performance liquid chromatography and used for the determination of safranal in Saffron samples. Reasonable agreement was observed between the results of the cooling‐assisted headspace liquid‐phase microextraction high‐performance liquid chromatography method and those obtained by a validated ultrasound‐assisted solvent extraction procedure.     

High‐density extraction solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction combined with MEKC for detection of chlorophenols in water samples

For the first time, the high‐density solvent‐based solvent de‐emulsification dispersive liquid–liquid microextraction (HSD‐DLLME) was developed for the fast, simple, and efficient determination of chlorophenols in water samples followed by field‐enhanced sample injection with reverse migrating micelles in CE. The extraction of chlorophenols in the aqueous sample solution was performed in the presence of extraction solvent (chloroform) and dispersive solvent (acetone). A de‐emulsification solvent (ACN) was then injected into the aqueous solution to break up the emulsion, the obtained emulsion cleared into two phases quickly. The lower layer (chloroform) was collected and analyzed by field‐enhanced sample injection with reverse migrating micelles in CE. Several important parameters influencing the extraction efficiency of HSD‐DLLME such as the type and volume of extraction solvent, disperser solvent and de‐emulsification solvent, sample pH, extraction time as well as salting‐out effects were optimized. Under the optimized conditions, the proposed method provided a good linearity in the range of 0.02–4 μg/mL, low LODs (4 ng/mL), and good repeatability of the extractions (RSDs below 9.3%, n = 5). And enrichment factors for three phenols were 684, 797, and 233, respectively. This method was then utilized to analyze two real environmental samples from wastewater and tap water and obtained satisfactory results. The obtained results indicated that the developed method is an excellent alternative for the routine analysis in the environmental field.     

Rapid monitoring of carvacrol in plants and herbal medicines using matrix solid-phase dispersion and gas chromatography flame ionisation detector

Matrix solid-phase dispersion (MSPD) method coupled with gas chromatography flame ionisation detector as a quick and easy extraction technique has been developed to extract carvacrol from plants and herbal medicines. Influence of important parameters on the MSPD method efficiency, such as the sorbent material, the ratio of sample to sorbent material, elution solvent and volume of the elution solvent has been evaluated and optimised. Carvacrol was successfully extracted by diatomaceous earth as sorbent with 350 μL of dichloromethane as elution solvent. The calibration curve showed good linearity (r² = 0.9965) and precision (RSD < 8.16%) in the concentration range of 0.5–100 μg mL^? 1 for carvacrol. The limit of detection and limit of quantification were 0.1 and 0.5 μg mL^? 1, respectively. The recoveries were in the range of 74.4–80.5% with relative standard deviation (RSD) values ranging from 8.4% to 9.8%. The reported MSPD extraction method revealed to be simpler and faster than conventional methods used to quantify carvacrol from plants and herbal medicines.     

Determination of parabens and endocrine-disrupting alkylphenols in soil by gas chromatography–mass spectrometry following matrix solid-phase dispersion or in-column microwave-assisted extraction: a comparative study

Two rapid methods were evaluated for the simultaneous extraction of seven parabens and two alkylphenols from soil based on matrix solid-phase dispersion (MSPD) and microwave-assisted extraction (MAE). Soil extracts were derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide and analyzed by gas chromatography with mass spectrometry. Extraction and clean-up of samples were carried out by both methods in a single step. A glass sample holder, inside the microwave cell, was used in MAE to allow the simultaneous extraction and clean-up of samples and shorten the MAE procedure. The detection limits achieved by MSPD were lower than those obtained by MAE because the presence of matrix interferences increased with this extraction method. The extraction yields obtained by MSPD and MAE for three different types of soils were compared. Both procedures showed good recoveries and sensitivity for the determination of parabens and alkylphenols in two of the soils assayed, however, only MSPD yielded good recoveries with the other soil. Finally, MSPD was applied to the analysis of soils collected in different sites of Spain. In most of the samples analyzed, methylparaben and butylparaben were detected at levels ranging from 1.21 to 8.04 ng g⁻¹ dry weight and 0.48 to 1.02 ng g⁻¹ dry weight, respectively.     

Determination of 3,5,6‐trichloro‐2‐pyridinol,phoxim and chlorpyrifos‐methyl in water samples using a new pretreatment method coupled with high‐performance liquid chromatography

A novel low‐density solvent‐based vortex‐assisted surfactant‐enhanced‐emulsification liquid–liquid microextraction with the solidification of floating organic droplet method coupled with high‐performance liquid chromatography was developed for the determination of 3,5,6‐trichloro‐2‐pyridinol, phoxim and chlorpyrifos‐methyl in water samples. In this method, the addition of a surfactant could enhance the speed of the mass transfer from the sample solution into the extraction solvent. The extraction solvent could be dispersed into the aqueous by the vortex process. The main parameters affecting the extraction efficiency were investigated and the optimum conditions were established as follows: 80 μL 1‐undecanol as extraction solvent, 0.2 mmol/L of Triton X‐114 selected as the surfactant, the vortex time was fixed at 60 s with the vortex agitator set at 3000 rpm, the concentration of acetic acid in sample solution was 0.4% v/v and 1.0 g addition of NaCl. Under the optimum conditions, the enrichment factors were from 172 to 186 for the three analytes. The linear ranges were from 0.5 to 500 μg/L with a coefficient of determination (r²) of between 0.9991 and 0.9995. Limits of detections were varied between 0.05 and 0.12 μg/L. The relative standard deviations (n = 6) ranged from 0.26 to 2.62%.     

Development of single‐drop microextraction and simultaneous derivatization followed by GC‐MS for the determination of aliphatic amines in tobacco

In this work, for the first time, headspace (HS) single‐drop microextraction and simultaneous derivatization followed by GC‐MS was developed to determine the aliphatic amines in tobacco samples. In the HS extraction procedure, the mixture of derivatization reagent and organic solvent was employed as the extraction solvent for HS single‐drop microextraction and in situ derivatization of aliphatic amine in the samples. Fast extraction and simultaneous derivatization of the analytes were performed in a single step, and the obtained derivatives in the microdrop extraction solvent were analyzed by GC‐MS. The optimized experiment conditions were: sample preparation temperature of 80°C and time of 30 min, HS extraction solvent (the mixture of benzyl alcohol and 2,3,4,5,6‐pentafluorobenzaldehyde) volume of 2.0 μL, extraction time of 90 s. With the optimal conditions, the method validations were also studied. The method has good linearity (R² more than 0.99), accepted precision (RSD less than 13%), good recovery (98–104%) and low limit of detection (0.11–0.97 μg/g). Finally, the proposed technique was successfully applied to the analyses of aliphatic amines in tobacco samples of seven different brands. It was further demonstrated that the proposed method offered a simple, low‐cost and reliable approach to determine aliphatic amines in tobacco samples.     

MSPD procedure for determining buprofezin,tetradifon, vinclozolin,and bifenthrin residues in propolis by gas chromatography–mass spectrometry

A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine bifenthrin, buprofezin, tetradifon, and vinclozolin in propolis using gas chromatography–mass spectrometry in selected ion monitoring mode (GC–MS, SIM). Different method conditions were evaluated, for example type of solid phase (C₁₈, alumina, silica, and Florisil), the amount of solid phase and eluent (n-hexane, dichloromethane, dichloromethane–n-hexane (8:2 and 1:1, v/v) and dichloromethane–ethyl acetate (9:1, 8:2 and 7:3, v/v)). The best results were obtained using 0.5 g propolis, 1.0 g silica as dispersant sorbent, 1.0 g Florisil as clean-up sorbent, and dichloromethane–ethyl acetate (9:1, v/v) as eluting solvent. The method was validated by analysis of propolis samples fortified at different concentration levels (0.25 to 1.0 mg kg⁻¹). Average recoveries (four replicates) ranged from 67% to 175% with relative standard deviation between 5.6% and 12.1%. Detection and quantification limits ranged from 0.05 to 0.10 mg kg⁻¹ and 0.15 to 0.25 mg kg⁻¹ propolis, respectively.     

Quantitative analysis of sesquiterpenes and comparison of three Curcuma wenyujin herbal medicines by micro matrix solid phase dispersion coupled with MEEKC

A simple, efficient and environmental friendly method was proposed for determining five sesquiterpenoids of Curcuma wenyujin by MSPD extraction coupled with MEEKC separation. Molecular sieve was applied as a solid support for extraction of sesquiterpenoids for the first time. Various parameters affecting extraction and separation efficiency were investigated. The optimized conditions involved dispersing sample (200 mg) with 200 mg of TS‐1 for 150 s and using 1000 μL of methanol to elute five target analytes. Finally, they were well separated by using a running buffer containing 1.3% SDS, 5.0% 1‐butanol, 0.5% ethyl acetate and 10% acetonitrile in 10 mM borate buffer at pH 9.0. Consequently, the developed method was fully validated and successfully applied to determine the five sesquiterpenoids including curdine, curcumenol, germacrone, furanodiene and β‐elemene in Curcuma wenyujin origin's Chinese herbal medicines. Furthermore, hierarchical cluster analysis was performed based on the contents of target compounds for distinguishing steamed and non‐steamed drugs. The present study provided a promising method for fast investigation and discrimination of chemical difference in steam & non‐steamed Chinese medicines from Curcuma wenyujin origin.     

Development of a novel hollow‐fiber liquid‐phase microextraction based on oil‐in‐salt and its comparison with conventional one

A novel hollow‐fiber liquid‐phase microextraction based on oil‐in‐salt was proposed and introduced for the simultaneous extraction and enrichment of the main active compounds of hesperidin, honokiol, shikonin, magnolol, emodin, and β,β′‐dimethylacrylshikonin in a formula of Zi‐Cao‐Cheng‐Qi decoction and the single herb, Fructus Aurantii Immaturus , Cortex Magnoliae Officinalis , Radix et Rhizoma , and Lithospermum erythrorhizon , composing the formula prior to their analysis by high‐performance liquid chromatography. The results obtained by the proposed procedure were compared with those obtained by conventional hollow‐fiber liquid‐phase microextraction, and the proposed procedure mechanism was described. In the procedure, a hollow‐fiber segment was first immersed in organic solvent to fill the solvent in the fiber lumen and wall pore, and then the fiber was again immersed into sodium chloride solution to cover a thin salt membrane on the fiber wall pore filling organic solvent. Under the optimum conditions, the enrichment factors of the analytes were 0.6–109.4, linearities were 0.002–12 μg/mL with r ² ≥ 0.9950, detection limits were 0.6–12 ng/mL, respectively. The results showed that oil‐in‐salt hollow‐fiber liquid‐phase microextraction is a simple and effective sample pretreatment procedure and suitable for the simultaneous extraction and concentration of trace‐level active compounds in traditional Chinese medicine.     

Low‐density‐solvent‐based air‐assisted liquid–liquid microextraction followed by gas chromatography with flame ionization detection for the determination of synthetic phenolic antioxidants in milk samples

A simple and rapid sample pretreatment technique termed low‐density‐solvent‐based air‐assisted liquid–liquid microextraction has been developed for the extraction and preconcentration of three synthetic phenolic antioxidants including butylated hydroxyanisole, butylated hydroxytoluene, and tert‐butyl hydroquinone from milk samples prior to their analysis by gas chromatography with flame ionization detection. In this method, initially trichloroacetic acid as a proteins precipitation agent is added to the sample, and then it is sonicated and centrifuged. The obtained aqueous phase is removed and the analytes extracted by the proposed method using a low‐density organic solvent. Some important parameters such as type and volume of extraction solvent, ionic strength, pH, and centrifugation rate and time were studied. Under the optimum conditions, enrichment factors were obtained in the range of 501–614. LODs and quantification were between 0.76–1.16 and 2.66–3.96 ng mL^–1, respectively. This method is rapid and requires less than 15 min for sample preparation.     

Matrix Solid-Phase Dispersion Extraction and UPLC Determination of Sudan Dyes in Chili Powder

A new method involving matrix solid-phase dispersion (MSPD) extraction and UPLC in conjunction with photodiode array detection was developed for the rapid and simple determination of Sudan dyes in chili powder. Separation of Sudan I, Sudan II, Sudan III, and Sudan IV was achieved within 2 min on the 1.7 μm Acquity UPLC BEH C18 column by using gradient elution with a mobile phase consisting of acetonitrile–water at a flow rate of 0.5 mL min^?1. Optimization of MSPD extraction parameters, such as type of solid sorbent and elution solvent were carried out. Optimal conditions selected for MSPD extraction were 0.25 g of sample, 0.5 g of silica gel as solid sorbent, and 7 mL of acetonitrile–methanol (9:1, v/v) as eluting solvent. Limits of detection ranged between 0.25 and 0.30 mg kg^?1 depending on the dye involved. All analytes provided average recoveries from spiked (at 1, 1.5, and 2 mg kg^?1) chili powder samples ranging from 81 to 106%. The method was applied to the analysis of chili powder samples obtained from different countries.     

Evaluation of a method for the simultaneous quantification of N‐nitrosamines in water samples based on stir bar sorptive extraction combined with high‐performance liquid chromatography and diode array detection

A simple, sensitive, and reliable procedure based on stir bar sorptive extraction coupled with high‐performance liquid chromatography was applied to simultaneously extract and determine three semipolar nitrosamines including N‐nitrosodibutylamine, N‐nitrosodiphenylamine, and N‐nitrosodicyclohexylamine. To achieve the optimum conditions, the effective parameters on the extraction efficiency including desorption solvent and time, ionic strength of sample, extraction time, and sample volume were systematically investigated. The optimized extraction procedure was carried out by stir bars coated with polydimethylsiloxane. Under optimum extraction conditions, the performance of the proposed method was studied. The linear dynamic range was obtained in the range of 0.95–1000 ng/mL (r = 0.9995), 0.26–1000 ng/mL (r = 0.9988) and both 0.32–100 ng/mL (r = 0.9999) and 100–1000 ng/mL (r = 0.9998) with limits of detection of 0.28, 0.08, and 0.09 ng/mL for N‐nitrosodibutylamine, N‐nitrosodiphenylamine, and N‐nitrosodicyclohexylamine, respectively. The average recoveries were obtained >81%, and the reproducibility of the proposed method presented as intra‐ and interday precision were also found with a relative standard deviation <6%. Finally, the proposed method was successfully applied to the determination of trace amounts of selected nitrosamines in various water and wastewater samples and the obtained results were confirmed using mass spectrometry.     

Three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase for extraction and preconcentration of main active compounds in a traditional Chinese medicinal formula

A three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase was developed and coupled with high‐performance capillary electrophoresis for the simultaneous extraction, enrichment, and determination of main active compounds (hesperidin, honokiol, shikonin, magnolol, emodin, and β,β′‐dimethylacrylshikonin) in a traditional Chinese medicinal formula. In this procedure, two hollow fibers, impregnated with n‐heptanol/n‐nonanol (7:3, v/v) mixture in wall pores as the extraction phase and a combination (9:1, v/v) of methyltrioctylammonium chloride/glycerol (1:3, n/n) and methanol in lumen as the acceptor phase, were immersed in the aqueous sample phase. The target analytes in the sample solution were first extracted through the organic phase, and further back‐extracted to the acceptor phase during the stirring process. Important extraction parameters such as types and composition of extraction solvent and deep eutectic solvent, sample phase pH, stirring rate, and extraction time were investigated and optimized. Under the optimal conditions, detection limits were 0.3–0.8 ng/mL with enrichment factors of 6–114 for the analytes and linearities of 0.001–13 μg/mL (r² ≥ 0.9901). The developed method was successfully applied to the simultaneous extraction and concentration of the main active compounds in a formula of Zi‐Cao‐Cheng‐Qi decoction with the major advantages of convenience, effectiveness, and environmentally friendliness.     

Preconcentration Ultra Trace of Cd(II) in Water Samples Using Dispersive Liquid‐Liquid Microextraction with Salen(N,N′‐Bis(Salicylidene)‐Ethylenediamine) and Determination Graphite Furnace Atomic Absorption Spectrometry

Dispersive liquid–liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g Salen(N,N′‐bis(salicylidene)ethylenediamine) (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with Salen(N,N′‐bis(salicylidene)‐ethylenediamine), and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 122 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the range of 2‐21 ng L^?1 with a detection limit of 0.5 ng L^?1. The relative standard deviation (R.S.D._s) for ten replicate measurements of 20 ng L^?1 of cadmium was 2.9%. The relative recoveries of cadmium in tap, sea and rain water samples at a spiking level of 5 and 10 ng L^?1 are 99, 94, 97 and 96%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on‐line liquid‐liquid extraction, single drop microextraction (SDME), on‐line solid phase extraction (SPE) and co‐precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).     

Ultrapreconcentration and determination of organophosphorus pesticides in water by solid‐phase extraction combined with dispersive liquid–liquid microextraction and high‐performance liquid chromatography

Solid‐phase extraction coupled with dispersive liquid–liquid microextraction was developed as an ultra‐preconcentration method for the determination of four organophosphorus pesticides (isocarbophos, parathion‐methyl, triazophos and fenitrothion) in water samples. The analytes considered in this study were rapidly extracted and concentrated from large volumes of aqueous solutions (100 mL) by solid‐phase extraction coupled with dispersive liquid–liquid microextraction and then analyzed using high performance liquid chromatography. Experimental variables including type and volume of elution solvent, volume and flow rate of sample solution, salt concentration, type and volume of extraction solvent and sample solution pH were investigated for the solid‐phase extraction coupled with dispersive liquid–liquid microextraction with these analytes, and the best results were obtained using methanol as eluent and ethylene chloride as extraction solvent. Under the optimal conditions, an exhaustive extraction for four analytes (recoveries >86.9%) and high enrichment factors were attained. The limits of detection were between 0.021 and 0.15 μg/L. The relative standard deviations for 0.5 μg/L of the pesticides in water were in the range of 1.9–6.8% (n = 5). The proposed strategy offered the advantages of simple operation, high enrichment factor and sensitivity and was successfully applied to the determination of four organophosphorus pesticides in water samples.