A novel, environmentally friendly dispersive liquid-liquid microextraction procedure for the determination of copper

A novel, simple and environmentally friendly procedure for copper determination has been developed. The method is based on the formation of an ion associate of Cu(I) with 1,3,3-trimethyl-2-[5-(1,3,3-trimethyl-1,3-dihydroindol-2-ylidene)-penta-1,3-dienyl]-3H-indolium (DIDC) in the presence of chloride ions as ligand, followed by dispersive liquid-liquid microextraction (DLLME) of the formed ion associate into organic phase and UV-Vis spectrophotometric detection. The following experimental conditions were used: pH 3, 0.24 mol L^− 1 chloride ions, 0.06 mmol L^− 1 DIDC. The effect of the nature of the extraction solvent, auxiliary solvent and disperser solvent used was studied. A mixture of amyl acetate, tetrachloromethane, and methanol in a 1:1:3 v/v/v ratio was selected for the DLLME procedure. The absorbance of the coloured extracts at 640 nm wavelength obeys Beer's law in the range 0.020-0.090 mg L^− 1 of Cu. The limit of detection calculated from a blank test (n = 10) based on 3s is 0.005 mg L^− 1 of Cu. The developed procedure was applied to the analysis of water samples. The suggested DLLME is compared with two procedures previously reported from our laboratory based on (1) conventional liquid-liquid extraction, and (2) sequential injection extraction performed in a dual-valve sequential injection system. The advantages and disadvantages of each method are discussed.     

A novel approach in dispersive liquid-liquid microextraction based on the use of an auxiliary solvent for adjustment of density: UV-VIS spectrophotometric and graphite furnace atomic absorption spectrometric determination of gold based on ion pair formation

This paper presents a novel approach to dispersive liquid-liquid microextraction (DLLME), based on the use of an auxiliary solvent for the adjustment of density. The procedure utilises a solvent system consisting of a dispersive solvent, an extraction solvent and an auxiliary solvent, which allows for the use of solvents having a density lower than that of water as an extraction solvent while preserving simple phase separation by centrifugation. The suggested approach could be an alternative to procedures described in the literature in recent months and which have been devoted to solving the same problem. The efficiency of the suggested approach is demonstrated through the determination of gold based on the formation of the ion pair [Au(CN)₂]⁻ anion with Astra Phloxine (R) reagent and its extraction using the DLLME procedure with subsequent UV-VIS spectrophotometric and graphite furnace atomic absorption spectrometric detection. The optimum conditions were found to be: pH 3; 0.8 mmol L⁻¹ K₄[Fe(CN)₆]; 0.12 mmol L⁻¹ R; dispersive solvent, methanol; extraction solvent, toluene; auxiliary solvent, tetrachloromethane. The calibration plots were linear in the ranges 0.39-4.7 mg L⁻¹ and 0.5-39.4 μg L⁻¹ for UV-VIS and GFAAS detection, respectively; thus enables the application of the developed method in two ranges differing from one from another by three orders of magnitude. The presented approach can be applied to the development of DLLME procedures for the determination of other compounds extractable by organic solvents with a density lower than that of water.     

Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple,rapid and sensitive method for the determination of bisphenol A in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142 μL of chloroform, disperser solvent: 2.0 mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100 μg L⁻¹ with the detection limit of 0.07 μg L⁻¹ for BPA. The relative standard deviation (RSD, n = 5) for the extraction and determination of 100 μg L⁻¹ of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.     

Sequential injection dispersive liquid-liquid microextraction based on fatty alcohols and poly(etheretherketone)-turnings for metal determination by flame atomic absorption spectrometry

A novel, simple and efficient sequential injection (SI) on-line dispersive liquid-liquid microextraction (DLLME) procedure was described and was demonstrated for the assay of trace silver determination by flame atomic absorption spectrometry (FAAS). Fatty alcohols, such as 1-undecanol and 1-dodecanol, were examined as extraction solvents at microlitre volume, overcoming a major problem of the DLLME methods, the high toxicity of the extraction solvents used. Furthermore, the extractant fine droplets can be easily separated from the aqueous phase using a micro-column packed with a novel hydrophobic sorbent material, poly(etheretherketone)-turnings. In this method fine droplets of 1-dodecanol were on-line generated and dispersed into the stream of aqueous sample. By this continuous process, silver diethyldithiocarbamate (Ag-DDTC) complex was formed and extracted into the dispersed extraction solvent. No specific conditions such as ice bath for low temperature or special tools are required for extractant isolation. All significant parameters that influence the efficiency of the system such as sample acidity, concentration of complexing reagent and extraction solvent, flow-rate of disperser and sample solution as well as the preconcentration time were investigated and optimized by full factorial design. Under the optimized conditions a detection limit of 0.15 μg L⁻¹, a relative standard deviation (RSD) of 2.9% at 5.00 μg L⁻¹ Ag(I) concentration level and an enhancement factor of 186 were obtained. The developed method was evaluated by analyzing certified reference material and was applied successfully to the analysis of environmental water samples.     

Displacement-dispersive liquid-liquid microextraction coupled with graphite furnace atomic absorption spectrometry for the selective determination of trace silver in environmental and geological samples

A novel displacement-dispersive liquid-liquid microextraction method was developed for the selective determination of trace silver in complicated samples by graphite furnace atomic absorption spectrometry. This method involves two steps of dispersive liquid-liquid microextraction (DLLME). Firstly, copper ion reacted with diethyldithiocarbamate (DDTC) to form Cu-DDTC complex and extracted with DLLME procedure using carbon tetrachloride (extraction solvent) and methanol (dispersive solvent); then, the sedimented phase was dispersed into the sample solution containing silver ion with methanol and another DLLME procedure was carried out. Because the stability of Ag-DDTC is larger than that of Cu-DDTC, Ag⁺ can displace Cu²⁺ from the pre-extracted Cu-DDTC and thus the preconcentration of Ag⁺ was achieved. Potential interference from co-existing transition metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu²⁺ from Cu-DDTC complex. The tolerance limits for the co-existing ions were increased by a long way compared with conventional DLLME. Under the optimal conditions, the limit of detection was 20 ng L⁻¹ (3σ) for silver with a sample volume of 5.0 mL, and an enhancement factor of 72 was achieved. The proposed method was successfully applied to determine of trace silver in some environmental and geological samples with satisfactory results.     

Determination of priority pollutants in aqueous samples by dispersive liquid–liquid microextraction

A dispersive liquid–liquid microextraction (DLLME) method followed by high-performance liquid chromatography–triple quadrupole mass spectrometry has been developed for the simultaneous determination of linear alkylbenzene sulfonates (LAS C₁₀, C₁₁, C₁₂, and C₁₃), nonylphenol (NP), nonylphenol mono- and diethoxylates (NP₁EO and NP₂EO), and di-(2-ethylhexyl)phthalate (DEHP). The applicability of the method has been tested by the determination of the above mentioned organic pollutants in tap water and wastewater. Several parameters affecting DLLME, such as, the type and volume of the extraction and disperser solvents, sample pH, ionic strength and number of extractions, have been evaluated. Methanol (1.5 mL) was selected among the six disperser solvent tested. Dichlorobenzene (50 μL) was selected among the four extraction solvent tested. Enrichment factor achieved was 80. Linear ranges in samples were 0.01–3.42 μg L⁻¹ for LAS C₁₀–₁₃ and NP₂EO, 0.09–5.17 μg L⁻¹ for NP₁EO, 0.17–9.19 μg L⁻¹ for NP and 0.40–17.9 μg L⁻¹ for DEHP. Coefficients of correlation were higher than 0.997. Limits of quantitation in tap water and wastewater were in the ranges 0.009–0.019 μg L⁻¹ for LAS, 0.009–0.091 μg L⁻¹ for NP, NP₁EO and NP₂EO and 0.201–0.224 μg L⁻¹ for DEHP. Extraction recoveries were in the range from 57 to 80%, except for LAS C₁₀ (30–36%). The method was successfully applied to the determination of these pollutants in tap water and effluent wastewater from Seville (South of Spain). The DLLME method developed is fast, easy to perform, requires low solvent volumes and allows the determination of the priority hazardous substances NP and DEHP (Directive 2008/105/EC).     

Dispersive liquid–liquid microextraction applied to isolation and concentration of alkylphenols and their short-chained ethoxylates in water samples

Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography with fluorescence detector was applied for the determination of alkylphenols and their short-chained ethoxylates in water samples. Development of DLLME procedure included optimisation of some important parameters such as kind and volume of extracting and dispersing solvents. Under optimised conditions 50 μL of trichloroethylene in 1.5 mL of acetone were rapidly injected into 5 mL of a water sample. After centrifuging the organic phase containing the analytes was taken for evaporation with a gentle nitrogen purge and reconstituted to 50 μL of acetonitrile. The aliquot of this solution was analysed with the use of HPLC. For octylphenol (OP) and octylphenol ethoxylates (OPEOs) linearity was satisfactory in the range 8–1000 μg L⁻¹ and for nonylphenol (NP) and nonylphenol ethoxylates (NPEOs) linearity was in the range from 50 to about 3000 μg L⁻¹. Limit of quantitation was 0.1 μg L⁻¹ for OP and OPEOs and 0.3 μg L⁻¹ for NP and NPEOs. Satisfactory recoveries between 66 and 79% were obtained for environmental samples. The results showed that DLLME is a simple, rapid and sensitive analytical method for the preconcentration of trace amounts of alkylphenols and their ethoxylates in environmental water samples.     

Determination of octylphenol and nonylphenol in aqueous sample using simultaneous derivatization and dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

A simple and fast sample preparation method for the determination of nonylphenol (NP) and octylphenol (OP) in aqueous samples by simultaneous derivatization and dispersive liquid–liquid microextraction (DLLME) was investigated using gas chromatography–mass spectrometry (GC/MS). In this method, a combined dispersant/derivatization catalyst (methanol/pyridine mixture) was firstly added to an aqueous sample, following which a derivatization reagent/extraction solvent (methyl chloroformate/chloroform) was rapidly injected to combine in situ derivatization and extraction in a single step. After centrifuging, the sedimented phase containing the analytes was injected into the GC port by autosampler for analysis. Several parameters, such as extraction solvent, dispersant solvent, amount of derivatization reagent, derivatization and extraction time, pH, and ionic strength were optimized to obtain higher sensitivity for the detection of NP and OP. Under the optimized conditions, good linearity was observed in the range of 0.1–1000 μg L⁻¹ and 0.01–100 μg L⁻¹ with the limits of detection (LOD) of 0.03 μg L⁻¹ and 0.002 μg L⁻¹ for NP and OP, respectively. Water samples collected from the Pearl River were analyzed with the proposed method, the concentrations of NP and OP were found to be 2.40 ± 0.16 μg L⁻¹ and 0.037 ± 0.001 μg L⁻¹, respectively. The relative recoveries of the water samples spiked with different concentrations of NP and OP were in the range of 88.3–106.7%. Compared with SPME and SPE, the proposed method can be successfully applied to the rapid and convenient determination of NP and OP in aqueous samples.     

A procedure for determination of cobalt in water samples after dispersive liquid–liquid microextraction

In this work, a procedure for preconcentration of cobalt using dispersive liquid–liquid microextraction (DLLME) with the reagent Br-TAO as complexing reagent was developed. The procedure is based on a ternary system of solvents, where appropriate amounts of the extraction solvent, disperser solvent and the chelating agent Br-TAO are directly injected into an aqueous solution containing Co(II). A cloudy mixture is formed and the ions are extracted in the fine droplets of the extraction solvent. After extraction, the phase separation is performed with a rapid centrifugation, and cobalt is determined in the enriched phase by FAAS. Under the optimized conditions, the detection limit obtained was 0.9 µg L^{− 1}. The enrichment factor and the consumptive index were 16 and 0.31 mL, respectively. The accuracy of the method was tested by the determination of cobalt in certified reference material of spinach leaves, NIST 1570a. The proposed procedure was successfully applied to the determination of cobalt in water samples.     

Trace determination of dichlorodiphenyltrichloroethane and its main metabolites in environmental water samples with dispersive liquid–liquid microextraction in combination with high performance liquid chromatography and ultraviolet detector

Dichlorodiphenyltrichloroethane,1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its main metabolites have been paid much more attention, and present paper describes a new process for the rapid determination of such pollutants in environmental water samples based on dispersive liquid–liquid microextraction (DLLME) and high performance liquid chromatography with ultraviolet detector, which has merits such as high enrichment factor and sensitivity, low cost and easy to operate. Significant parameters such as extraction solvent and dispersive solvent type and volume, pH, extraction time and centrifuging time, which would have important impact on the enrichment of target pollutants, have been investigated in detail. The results exhibited that excellent performance could be achieved with carbon tetrachloride and acetonitrile as the extraction solvent and dispersive solvent, respectively. Under the optimal conditions, excellent linear relationship was gained in the range of 1.0–50 μg L⁻¹, and detection limits were in the range of 0.32–0.51 μg L⁻¹. The precisions of the proposed method were in the range of 2.80–7.50% (RSD). The proposed method was validated with real water samples, and the results indicated the spiked recoveries were in the range of 85.58–119.6% and the established method was very good and competitive in the determination of DDT and its metabolites.     

Preparation of a carbon ceramic electrode modified by 4-(2-pyridylazo)-resorcinol for determination of trace amounts of silver

A 4-(2-pyridylazo)-resorcinol (PAR)-modified carbon ceramic electrode (CCE) prepared by the sol-gel technique has been reported for the first time in this paper. By immersing the CCE in aqueous solution of PAR (0.001 mol L⁻¹), after a short period of time, a thin film of PAR was rapidly formed on the surface of the electrode due to its strong adsorption properties. A differential pulse anodic stripping voltammetric (DPASV) method was developed for determination of Ag(I) at the modified carbon ceramic electrode. The analysis procedure consisted of an open circuit accumulation step in a sample solution which was continuously stirred for 12 min. This was followed by replacing the medium with a clean solution where the accumulated Ag(I) was reduced for 15 s in −0.6 V. Then, the potential was scanned from −0.2 to +0.2 V to obtain the voltammetric peak. The detection limit of silver(I) was 0.123 μg L⁻¹, and for seven successive determinations of 10, 100 and 200 μg L⁻¹ Ag(I), the relative standard deviations were 2.1, 1.4 and 1.03%, respectively. The calibration curve was linear for 0.5-300 μg L⁻¹ silver(I). The procedure was applied to determine silver(I) in X-ray photographic films and super-alloy samples.     

In-syringe demulsified dispersive liquid–liquid microextraction and high performance liquid chromatography–mass spectrometry for the determination of trace fungicides in environmental water samples

An in-syringe demulsified dispersive liquid–liquid microextraction (ISD–DLLME) technique was developed using low-density extraction solvents for the highly sensitive determination of the three trace fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water samples by high performance liquid chromatography–mass spectrometry chromatography–diode array detector/electrospray ionisation mass spectrometry. In the proposed technique, a 5-mL syringe was used as an extraction, separation and preconcentration container. The emulsion was obtained after the mixture of toluene (extraction solvent) and methanol (dispersive solvent) was injected into the aqueous bulk of the syringe. The obtained emulsion cleared into two phases without centrifugation, when an aliquot of methanol was introduced as a demulsifier. The separated floating organic extraction solvent was impelled and collected into a pipette tip fitted to the tip of the syringe. Under the optimal conditions, the enrichment factors for azoxystrobin, diethofencarb and pyrimethanil were 239, 200, 195, respectively. The limits of detection, calculated as three times the signal-to-noise ratio (S N⁻¹), were 0.026 μg L⁻¹ for azoxystrobin, 0.071 μg L⁻¹ for diethofencarb and 0.040 μg L⁻¹ for pyrimethanil. The repeatability study was carried out by extracting the spiked water samples at concentration levels of 0.02 μg mL⁻¹ for all the three fungicides. The relative standard deviations varied between 4.9 and 8.2% (n = 5). The recoveries of all the three fungicides from tap, lake and rain water samples at spiking levels of 0.2, 1, 5 μg L⁻¹ were in the range of 90.0–105.0%, 86.0–114.0% and 88.6–110.0%, respectively. The proposed ISD–DLLME technique was demonstrated to be simple, practical and efficient for the determination of different kinds of fungicide residues in real water samples.     

A dispersive liquid-liquid microextraction procedure for determination of boron in water after ultrasound-assisted conversion to tetrafluoroborate

A novel, simple and green procedure is presented for the determination of boron. The method is based on ultrasound-assisted conversion of boron to tetrafluoroborate anion and the formation of an ion pair between BF₄⁻ and Astra Phloxine reagent (R), followed by dispersive liquid-liquid microextraction of the ion pair formed and subsequent UV-vis spectrophotometric detection. The conversion of boron to tetrafluoroborate anion is performed in an acidic medium of 0.9 mol L⁻¹ H₂SO₄ in the presence of 0.1 mol L⁻¹ F^- by means of 10 min of ultrasonication. The extraction of the ion pair formed between BF₄⁻ and R (1 × 10⁻⁴ mol L⁻¹ R) is carried out by dispersive liquid-liquid microextraction using 0.5 mL of amyl acetate (as extraction solvent), tetrachloromethane (as auxiliary solvent) and acetonitrile (as dispersive solvent) in a ratio of 1:1:2. The absorbance of the coloured extracts obeys Beer's law in the range 0.22-18.7 mg L⁻¹ of B(III) at 553 nm wavelength. The limit of detection calculated from a blank test (n = 10) based on 3 s is 0.015 mg L⁻¹ of B(III). The method was applied to the determination of boron in mineral waters.     

Optimization of dispersive liquid-liquid microextraction coupled with inductively coupled plasma-optical emission spectrometry with the aid of experimental design for simultaneous determination of heavy metals in natural waters

In this study, dispersive liquid-liquid microextraction (DLLME) combined with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed for simultaneous preconcentration and trace determination of chromium, copper, nickel and zinc in water samples. Sodium diethyldithiocarbamate (Na-DDTC), carbon tetrachloride and methanol were used as chelating agent, extraction solvent and disperser solvent, respectively. The effective parameters of DLLME such as volume of extraction and disperser solvents, pH, concentration of salt and concentration of the chelating agent were studied by a (2^f−1) fractional factorial design to identify the most important parameters and their interactions. The results showed that concentration of salt and volume of disperser solvent had no effect on the extraction efficiency. In the next step, central composite design was used to obtain optimum levels of effective parameters. The optimal conditions were: volume of extraction solvent, 113 μL; concentration of the chelating agent, 540 mg L⁻¹; and pH, 6.70. The linear dynamic range for Cu, Ni and Zn was 1-1000 μg L⁻¹ and for Cr was 1-750 μg L⁻¹. The correlation coefficient (R²) was higher than 0.993. The limits of detection were 0.23-0.55 μg L⁻¹. The relative standard deviations (RSDs, C = 200 μg L⁻¹, n = 7) were in the range of 2.1-3.8%. The method was successfully applied to determination of Cr, Cu, Ni and Zn in the real water samples and satisfactory relative recoveries (90-99%) were achieved.     

Determination of UV filters in both soluble and particulate fractions of seawaters by dispersive liquid–liquid microextraction followed by gas chromatography–mass spectrometry

An analytical method to determine the total content (i.e., not only in the soluble fraction but also in the particulate one) of eight commonly used UV filters in seawater samples is presented for the first time. Dispersive liquid–liquid microextraction (DLLME) is used as microextraction technique to pre-concentrate the target analytes before their determination by gas chromatography–mass spectrometry (GC–MS). In order to release the UV filters from the suspended particles an ultrasound treatment is performed before DLLME. The ultrasound treatment time was studied in order to achieve a quantitative lixiviation of the target analytes. The type and volume of both disperser and extraction solvent, the sample volume, the pH and the ionic strength involved in the DLLME have been optimized to provide the best enrichment factors. Under the optimized conditions, the method was successfully validated showing good linearity, enrichment factors between 112 and 263 depending on the analyte, limits of detection and quantification in the low ng L⁻¹ range (10–30 ng L⁻¹ and 33–99 ng L⁻¹, respectively) and good intra- and inter-day repeatability (RSD <15%). No significant matrix effects were found. Finally, the method was satisfactorily applied to the analysis of three seawater samples from different origin. Results showed significant amounts of UV filters in the particulate fraction that would have been ignored if only the soluble fraction had been considered. This fact shows that the UV filters are also accumulated in the suspended particles contained in water, what should be taken into account from an environmental standpoint.     

Adsorptive Stripping Voltammetric Determination of Phenol at an Electrochemically Pretreated Carbon-Paste Electrode with Solid Paraffin as a Binder

An adsorptive stripping voltammetric method for determination of phenol at an electrochemically pretreated carbon-paste electrode has been developed. Solid paraffin was used as the binder of the carbon-paste electrode. The carbon-paste electrode was pretreated in the solution of 0.001 mol L⁻¹NaOH by holding it at +1.8 V (versus an Ag/AgCl electrode) for 5 min. On the pretreated electrode, the adsorption of phenol was greatly enhanced. Phenol was accumulated in NH₃–NH₄Cl (pH 9.25) medium at the potential of +0.1 V (versus Ag/AgCl electrode) for a certain time and then determined by second order differential anodic stripping voltammetry. An oxidative peak was observed at about +0.66 V. The relationship between second order peak current and phenol concentration was linear in the range of 2.5 × 10⁻⁷–5.0 × 10⁻⁶mol L⁻¹phenol, and the detection limit was 5.0 × 10⁻⁸mol L⁻¹. The method has been applied to the determination of phenol in tap water and waste water. The relative standard deviation (six determinations) was less than 3.5%.     

Automated on-line dispersive liquid–liquid microextraction based on a sequential injection system

A novel approach for sequential injection-dispersive liquid–liquid microextraction (SI-DLLME) has been suggested. The method is based on the aspiration and mixing of a sample and all required aqueous reagents in the holding coil of an SIA system, delivering it into a conical tube and adding in a mixture of extraction solvent, auxiliary solvent and disperser solvent at high flow rate, resulting in the formation of a cloudy state and the extraction of an analyte. The mixture of extraction and auxiliary solvent is immiscible with water and has a density significantly higher than that of water; consequently, the resulting fine droplets in the mixture, which contain the extracted analyte, are self-sedimented in a short time at the bottom of conical tube. Thus, no centrifugation and no use of a microcolumn are required for separation of the extraction phase. Afterwards, the extracted analyte is aspirated and transferred to a micro-volume Z-flow cell, and the absorbance is measured.The performance of the suggested approach is demonstrated by the SI-DLLME of thiocyanate ions in the form of ion associate with dimethylindocarbocyanine reagent, followed by spectrophotometric detection. A mixture of amyl acetate (as extraction solvent), tetrachloromethane (as auxiliary solvent) and acetonitrile (as disperser solvent) was selected for the DLLME procedure. The appropriate experimental conditions for conventional DLLME and automated SI-DLLME were investigated. The analytical performance of both these procedures was compared. The absorbance of the colored extracts at wavelength 555 nm obeys Beer's law in the range of 3.13–28.2 for conventional DLLME and 0.29–5.81 mg L^? 1 of SCN for SI-DLLME, and the limit of detection, calculated from a blank test based on 3 s, is 0.110 for conventional DLLME and 0.017 mg L^? 1 for SI-DLLME.     

Analysis of urinary neurotransmitters by capillary electrophoresis: sensitivity enhancement using field-amplified sample injection and molecular imprinted polymer solid phase extraction

Capillary electrophoresis (CE) has been investigated for the analysis of some neurotransmitters, dopamine (DA), 3-methoxytyramine (3-MT) and serotonin (5-hydroxytryptamine, 5-HT) at nanomolar concentrations in urine. Field-amplified sample injection (FASI) has been used to improve the sensitivity through the online pre-concentration samples. The cationic analytes were stacked at the capillary inlet between a zone of low conductivity - sample and pre-injection plug - and a zone of high conductivity - running buffer. Several FASI parameters have been optimized (ionic strength of the running buffer, concentration of the sample protonation agent, composition of the sample solvent and nature of the pre-injection plug). Best results were obtained using H₃PO₄–LiOH (pH 4, ionic strength of 80 mmol L⁻¹) as running buffer, 100 μmol L⁻¹ of H₃PO₄ in methanol–water 90/10 (v/v) as sample solvent and 100 μmol L⁻¹ of H₃PO₄ in water for the pre-injection plug.In these conditions, the linearity was verified in the 50–300 nmol L⁻¹ concentration range for DA, 3-MT and 5-HT with a determination coefficient (r²) higher than 0.99. The limits of quantification (10 nmol L⁻¹ for DA and 3-MT, 5.9 nmol L⁻¹ for 5-HT) were 500 times lower than those obtained with hydrodynamic injection. However, if this method is applied to the analysis of neurotransmitters in urine, the presence of salts in the matrix greatly reduces the sensitivity of the FASI/CE–UV method.Therefore, a solid phase extraction (SPE) on a dedicated imprinted polymer (MIP) was developed to extract specific neurotransmitters, catecholamines, metanephrines and indolamines, from urine. Matrix salts were thus discarded after sample extraction on AFFINIMIP™ Catecholamine & Metanephrine (100 mg) cartridge.Therefore, lower limits of quantification were determined in artificial urine (46 nmol L⁻¹ for DA, 11 nmol L⁻¹ for 3-MT and 6 nmol L⁻¹ for 5-HT).The application of this protocol MIP-SPE/FASI–CE–UV analysis of neurotransmitters in human urine gave rise to electropherograms with a very good base line and signal to noise ratios above 15.     

Dispersive solid-phase extraction followed by dispersive liquid–liquid microextraction for the determination of some sulfonylurea herbicides in soil by high-performance liquid chromatography

Dispersive solid-phase extraction (DSPE) combined with dispersive liquid–liquid microextraction (DLLME) has been developed as a new approach for the extraction of four sulfonylurea herbicides (metsulfuron-methyl, chlorsulfuron, bensulfuron-methyl and chlorimuron-ethyl) in soil prior to high-performance liquid chromatography with diode array detection (HPLC-DAD). In the DSPE-DLLME, sulfonylurea herbicides were first extracted from soil sample into acetone–0.15 mol L⁻¹ NaHCO₃ (2:8, v/v). The clean-up of the extract by DSPE was carried out by directly adding C₁₈ sorbent into the extract solution, followed by shaking and filtration. After the pH of the filtrate was adjusted to 2.0 with 2 mol L⁻¹ HCl, 60.0 μL chlorobenzene (as extraction solvent) was added into 5.0 mL of it for DLLME procedure (the acetone contained in the solution also acted as dispersive solvent). Under the optimum conditions, the enrichment factors for the compounds were in the range between 102 and 216. The linearity of the method was in the range from 5.0 to 200 ng g⁻¹ with the correlation coefficients (r) ranging from 0.9967 to 0.9987. The method detection limits were 0.5–1.2 ng g⁻¹. The relative standard deviations varied from 5.2% to 7.2% (n = 5). The relative recoveries of the four sulfonylurea herbicides from soil samples at spiking levels of 6.0, 20.0 and 60.0 ng g⁻¹ were in the range between 76.3% and 92.5%. The proposed method has been successfully applied to the analysis of the four target sulfonylurea herbicides in soil samples, and a satisfactory result was obtained.     

Nano polypyrrole-coated magnetic solid phase extraction followed by dispersive liquid phase microextraction for trace determination of megestrol acetate and levonorgestrel

The aim of the present work is combination of the advantages of magnetic solid phase extraction (MSPE) and dispersive liquid phase microextraction (DLLME) followed by filtration-based phase separation. A new pretreatment method was developed for trace determination of megestrol acetate and levonorgestrel by liquid chromatography/ultraviolet detection in biological and wastewater samples. After magnetic solid phase extraction, the eluent of MSPE was used as the disperser solvent for DLLME. Emulsion resulted from DLLME procedure was passed through the in-line filter for phase separation. Finally the retained analytes in the filter was washed with mobile phase of liquid chromatography and transferred to the column for separation. This approach offers the preconcentration factors of 3680 and 3750 for megestrol acetate and levonorgestrel, respectively. This guarantees determination of the organic compounds at trace levels. The important parameters influencing the extraction efficiency were studied and optimized. Under the optimal extraction conditions, a linear range of 0.05–50 ng mL⁻¹ (R² > 0.998) and limit of detection of 0.03 ng mL⁻¹ were obtained for megestrol acetate and levonorgestrel. Under optimal conditions, the method was successfully applied for determination of target analytes in urine and wastewater samples and satisfactory results were obtained (RSDs < 6.8%).