Sulfhydryl-functionalised magnetic nanoparticles as sorbent in dispersive solid-phase extraction for the rapid enrichment of mercury species from natural water samples

The sulfhydryl-functionalised core-shell Fe₃O₄@SiO₂ magnetic nanoparticles (Fe₃O₄@SiO₂–RSH MNPs)-based dispersive solid-phase extraction method was developed. The goal of this method is the extraction of mercury species from natural water samples. An interesting aspect of the method is that, thanks to the spontaneously aggregate, the MNPs with a sub-30-nm-size range could be fast and efficiently extracted by 0.45 μm pore size mixed cellulose esters membrane filter. Thus, the elution step can be conducted by passing small amounts eluent through the MNPs on the membrane. It is also found that addition of Ag⁺ to water sample could improve the elution efficiency, and furthermore, minimises the matrix effects during the extraction of mercury species from natural water samples. The feasibility of the method was studied, and extraction efficiency was evaluated. The results showed that, calculated at 5 ng/L spiked concentration levels, absolute recoveries were 89.4%, 91.9% and 64.2%, and enrichment factors (EFs) were 596, 613 and 428, for inorganic mercury, methylmercury and ethylmercury, respectively. The high EFs were achieved in 5 min of overall extraction time. The method was applied to groundwater and river water samples. The results showed that its suitability for use in fast extracting trace levels of mercury species from natural water samples.     

Determination of various inorganic anions and organic acids in the atmospheric particulate matter using capillary zone electrophoresis with indirect UV detection

Capillary zone electrophoresis with indirect UV detection was developed for the simultaneous analysis of inorganic anions and organic acids using a mixed solution of 2,6-pyridinedicarboxylic acid and cetyltrimethylammonium hydroxide as the background electrolyte (BGE). The parameters which influence the separation, such as indirect UV detection wavelength, BGE conditions, applied voltage and extraction conditions were investigated. Thirteen inorganic anions and organic acids were detected within 20 min. The calibration curves of each analyte were linear with correlation coefficients greater than 0.991. The relative standard deviations (n = 10) of the peak areas ranged from 0.6% to 3.3%. The detection limits for these species ranged from 0.4 to 1.4 mg/L at a signal-to-noise ratio of 3. The recovery rate of each analyte was more than 80% under optimised extraction conditions, except for nitrite. The proposed method was applied towards the analysis of inorganic anions and organic acids in the atmospheric particulate matter using an Andersen sampler. The particle size of the particulate matter was determined, but not the size of the anions.     

Determination of inorganic anions in ethyl acetate by ion chromatography with an electromembrane extraction method

In this work, the determination of inorganic anions in slightly water-soluble organic solvents (ethyl acetate) was realized by ion chromatography (IC) with a novel-efficient electromembrane extraction method. From an 8 mL ethyl acetate sample, three inorganic anions migrated through the pores of a polypropylene hollow fiber membrane, and into deionized water inside the lumen of the hollow fiber by the application of 600 V. The transport was forced by an electrical potential difference sustained over the liquid membrane, resulting in electrokinetic migration of inorganic anions from the donor compartment to the acceptor solution. After the electromembrane extraction, the acceptor solution was analyzed by IC with a sodium carbonate-sodium bicarbonate eluent. The applied voltage, stirring speed, and extraction time for controlling the extraction efficiency were optimized. Within 10 min of operation at 600 V, chloride, bromide, and sulfate were extracted with recoveries in the range 76-110%, which corresponded to a linear range of 0.01-1 mg/L. The procedure was applied to the analysis of inorganic anions in a real ethyl acetate sample and expands onto other slightly water-soluble organic solvents.     

An MSFIA system for mercury speciation based on an anion-exchange membrane

A new methodology for the in-line preconcentration, clean-up and speciation of mercury by use of an anion-exchange membrane is proposed. The speciation of mercury is based on retention of its tetrachloro complex onto the membrane while organic mercury flows freely through it. A multisyringe is used as a liquid driver and a cold vapour atomic fluorescence detector is employed to ensure a high sensitivity. Organic mercury is decomposed into to inorganic mercury by using a UV lamp. The carrier and reductant streams consist of 1.5% (m/v) hydrochloric acid and 2% (m/v) tin chloride, respectively. Certified reference material DORM-2 was digested with 37% hydrochloric acid and analysed directly without the need for extraction. The proposed system is more environmental friendly than the classical liquid-liquid extraction procedure. Mercury recoveries from spiked samples and the reference material were all close to 100%. An LOD of 14 and 16 ng/L was obtained for total and organic mercury, respectively, both with an RSD less than 1.3%.     

Determination of very low levels of dissolved mercury(II) and methylmercury in river waters by continuous flow with on-line UV decomposition and cold-vapor atomic fluorescence spectrometry after pre-concentration on a silica gel-2-mercaptobenzimidazol sorbent

A new, simple and sensitive method for the simultaneous determination of mercury(II) and methylmercury chloride at sub-ng l⁻¹ levels in river waters is described. Inorganic and organic mercury were preconcentrated from fresh water samples simultaneously on a laboratory-made column containing 2-mercaptobenzimidazol loaded on silica gel and then quantitatively eluted with 0.05 M KCN solution and 2.0 M HCl to desorp inorganic and methylmercury species, respectively. After irradiation with an intensive UV source, MeHg⁺ was decomposed and mercury vapours were generated from inorganic and organic mercury using an acidic SnCl₂ solution in a continuous flow system and were subsequently determined with a cold vapour atomic fluorescence (CV-AFS) spectrometer. Detection limits (3σ) were 0.07 and 0.05 ng l⁻¹ (as Hg) for mercury(II) chloride and methylmercury chloride, respectively. Relative standard deviations of method (%R.S.D.) were 8.8 and 10 for inorganic and organomercuric species in the river water, respectively. The analysis of real samples, taken from different rivers, showed that inorganic mercury levels ranged from 4.0±0.6 to 12±1 ng l⁻¹ (as Hg and 95% confidence limit) and methylmercury levels at 0.2±0.02 ng l⁻¹(as Hg).     

Determination of estrogens in wastewater using three-phase hollow fiber-mediated liquid-phase microextraction followed by HPLC

Three-phase hollow fiber-mediated liquid-phase microextraction followed by HPLC was used for the determination of three synthetic estrogens, namely diethylstilbestrol, dienestrol, and hexestrol, in wastewater. Extraction conditions including organic solvent, volume ratio between donor solution and acceptor phase, extraction time, stirring rate, donor phase and acceptor phase were optimized. The target compounds were extracted from a 10 mL aqueous sample at pH 1.5 (donor solution) through a 45 mm in length hollow polypropylene fiber that was immersed in 1-octanol in advance, and then the hollow fiber was filled with 10 microL 0.5 mol/L sodium hydroxide solution (acceptor phase). After a 40 min extraction, the acceptor phase was directly injected into an HPLC system for detection. Under the optimized extraction conditions, a large enrichment factor (more than 300-fold) was achieved for the three estrogens. The determination limit at an S/N of 3 ranged from 0.25 to 0.5 microg/L for the estrogens. The recovery ratio was more than 86% in the determination of these estrogens in wastewater.     

Dual-cloud point extraction as a preconcentration and clean-up technique for capillary electrophoresis speciation analysis of mercury

A novel dual-cloud point extraction (dCPE) technique is proposed in this paper for the sample pretreatment of capillary electrophoresis (CE) speciation analysis of mercury. In dCPE, cloud point was carried out twice in a sample pretreatment. First, four mercury species, methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) formed hydrophobic complexes with 1-(2-pyridylazo)-2-naphthol (PAN). After heating and centrifuging, the complexes were extracted into the formed Triton X-114 surfactant-rich phase. Instead of the direct injection or analysis, the surfactant-rich phase containing the four Hg species was treated with 150 microL 0.1% (m/v) l-cysteine aqueous solution. The four Hg species were then transferred back into aqueous phase by forming hydrophilic Hg-l-cysteine complexes. After dCPE, the aqueous phase containing the Hg-l-cysteine complexes was subjected into electrophoretic capillary for mercury speciation analysis. Because the concentration of Triton X-114 in the extract after dCPE was only around critical micelle concentration, the adsorption of surfactant on the capillary wall and its possible influence on the sample injection and separation in traditional CPE were eliminated. Plus, the hydrophobic interfering species were removed thoroughly by using dCPE resulted in significant improvement in analysis selectivity. Using 10 mL sample, 17, 15, 45, and 52 of preconcentration factors for EtHg, MeHg, PhHg, and Hg(II) were obtained. With CE separation and on-line UV detection, the detection limits were 45.2, 47.5, 4.1, and 10.0 microg L(-1) (as Hg) for EtHg, MeHg, PhHg, and Hg(II), respectively. As an analysis method, the present dCPE-CE with UV detection obtained similar detection limits as of some CE-inductively coupled plasma mass spectrometry (ICPMS) hyphenation technique, but with simple instrumental setup and obviously low costs. Its utilization for Hg speciation was validated by the analysis of the spiked natural water and tilapia muscle samples.     

A methodological study of mercury speciation using dogfish liver CRM (DOLT-2)

The purpose of the study was to optimise analytical methods for determination of the chemical speciation of mercury in studies of protective mechanisms of selenium. Optimisation of the methods was performed using CRM DOLT-2 (Dogfish liver), both in its original form and after separation of various fractions. The sample was homogenised with 10 mM Tris-HCl buffer (pH 7.6) and ultracentrifuged. The soluble phase obtained was applied to a size exclusion chromatography column (Sephadex G-75 column) for separation of various protein fractions. Total mercury (total Hg), monomethyl mercury (MeHg) and selenium (Se) were determined in whole dogfish liver tissue and its soluble and insoluble phases (pellet). Different approaches for determination of total Hg and MeHg were compared. Simultaneous determination of MeHg and inorganic mercury (Hg2+) was based on alkaline dissolution and/or acid leaching, followed by ethylation, room temperature precollection, isothermal gas chromatography (GC), pyrolysis and detection with cold vapour atomic fluorescence spectrometry (CVAFS). The sum of MeHg and Hg2+ was compared to total Hg results obtained by acid digestion and CVAAS detection. The accuracy of MeHg determination was checked by its determination using acid leaching at room temperature, solvent extraction, back extraction into Milli-Q water, ethylation, GC and CVAFS detection. For the insoluble phase it is recommended to use solvent extraction for MeHg and acid digestion CVAAS for total Hg. For determination of MeHg and Hg2+ in the lyophilised sample and water soluble fractions containing low concentrations of mercury species, the simultaneous measurement of MeHg and Hg2+ after alkaline dissolution is the most appropriate method.     

Supercritical fluid extraction of mercury species

Supercritical fluid extraction was used to recover organic and inorganic mercury species. Variations in pressure, water, methanol, and chelator create methods that allowed separation of inorganic from organic mercury species. When extracted using a compromised set of extraction conditions, the order of extraction was methyl, phenyl and inorganic mercury. For the individually optimized conditions, quantitative recoveries were observed. Level as low as 20 ppb were extracted and then determined using ICP.     

Single drop liquid-liquid-liquid microextraction of methamphetamine and amphetamine in urine

Single drop liquid-liquid-liquid microextraction (LLLME) combined with high performance liquid chromatography (HPLC)-UV detection was investigated for the determination of a popular drug of abuse, methamphetamine (MAP), and its major metabolite, amphetamine (AP), in urine samples. The target compounds were extracted from NaOH modified sample solution to a thin layer of organic solvent membrane, and back-extracted to an acidic acceptor drop suspended on the tip of a 50-microL HPLC syringe in the aforementioned organic layer. This syringe was also used for direct injection after extraction. Factors affecting extraction efficiency were studied. At optimal conditions, the overall enrichment factor (EF) was 500-fold for AP and 730-fold for MAP, respectively. The method exhibited a wide linear range (1.0-1500 microg/L), low detection limit (0.5 microg/L), and good repeatability (RSD<5.0%) for both analytes. The feasibility of the method was demonstrated by the analysis of human urine samples.     

Simultaneous extraction of acidic and basic drugs via on-chip electromembrane extraction

In the present work, a on-chip electromembrane extraction (CEME) was designed and employed for simultaneous extraction of mefenamic acid (MEF) and diclofenac (DIC), as acidic model analytes, and betaxolol (BET), as a basic model analyte, followed by HPLC-UV. The CEME consists of two polymethyl methacrylate (PMMA) parts which each part consists of two separated microfluidic channels. A polypropylene sheet membrane impregnated with an organic solvent was sandwiched between the parts. One of the parts was used as the flow path for the sample solution and the other one as holder for the acceptor phases. The separated microfluidic channels of the sample solution part were connected to each other using a small piece of a capillary tube and the sample solution was pumped through them by means of a micro-syringe pump. However, the acceptor phases of the acidic and basic analytes were separately kept stagnant in the two microfluidic channels during the extraction process. A d.c. potential was applied for migration of the analytes from sample solution through the organic membrane into the acceptor phases. All effective variables on the extraction efficiency of the analytes were optimized. Under the optimized conditions, preconcentration factors higher than 15 were achieved and the calibration curves were linear in the range of 10–500 μg L⁻¹ (r² > 0.9982). RSD% values (n = 4) and LODs were less than 7.1% and 5.0 μg L⁻¹. The results demonstrated that CEME could efficiently be used for the simultaneous analysis of acidic and basic analytes in biological samples.     

Determination of phenols in waters by stir membrane liquid-liquid-liquid microextraction coupled to liquid chromatography with ultraviolet detection

A simple and rapid method for the determination of eleven phenols in water samples is presented. The target analytes are isolated by stir membrane liquid-liquid microextraction working under the three-phase mode. An alkaline aqueous solution is used as extractant phase while octanol is selected as supported liquid membrane solvent. The target analytes are separated and determined by liquid chromatography (LC) with ultraviolet detection (UV). All the variables involved in the extraction process have been studied in depth. Low detection limits (in the range from 82.1 ng/L for phenol to 452 ng/L for 2,4,5-trichlorophenol) were obtained. The repeatability, expressed as relative standard deviation (RSD), varied between 1.3% (for 4-nitrophenol) and 8.0% (for 4-chlorophenol). The enrichment factors were in the range from 168 (for 2,4,5-trichlorophenol) to 395 (for 3-chlorophenol). The proposed procedure was applied for the direct determination of the eleven phenols in some real water samples including river, well and tap waters. The accuracy was evaluated by means of a recovery study, the results being in the range of 87-120%.     

Evaluation of dispersive liquid-liquid microextraction for the simultaneous determination of chlorophenols and haloanisoles in wines and cork stoppers using gas chromatography-mass spectrometry

Dispersive liquid-liquid microextraction (DLLME) coupled with gas chromatography-mass spectrometry (GC-MS) was evaluated for the simultaneous determination of five chlorophenols and seven haloanisoles in wines and cork stoppers. Parameters, such as the nature and volume of the extracting and disperser solvents, extraction time, salt addition, centrifugation time and sample volume or mass, affecting the DLLME were carefully optimized to extract and preconcentrate chlorophenols, in the form of their acetylated derivatives, and haloanisoles. In this extraction method, 1mL of acetone (disperser solvent) containing 30μL of carbon tetrachloride (extraction solvent) was rapidly injected by a syringe into 5mL of sample solution containing 200μL of acetic anhydride (derivatizing reagent) and 0.5mL of phosphate buffer solution, thereby forming a cloudy solution. After extraction, phase separation was performed by centrifugation, and a volume of 4μL of the sedimented phase was analyzed by GC-MS. The wine samples were directly used for the DLLME extraction (red wines required a 1:1 dilution with water). For cork samples, the target analytes were first extracted with pentane, the solvent was evaporated and the residue reconstituted with acetone before DLLME. The use of an internal standard (2,4-dibromoanisole) notably improved the repeatability of the procedure. Under the optimized conditions, detection limits ranged from 0.004 to 0.108ngmL(-1) in wine samples (24-220pgg(-1) in corks), depending on the compound and the sample analyzed. The enrichment factors for haloanisoles were in the 380-700-fold range.     

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters

The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg(2+)) and monomethylmercury compounds (MeHg) in natural water samples at the pg L(-1) level. The method is based on the simultaneous extraction of MeHg and Hg(2+)dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na(2)S, removal of H(2)S by purging with N(2), subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L(-1) for MeHg and 0.06 ng L(-1) for Hg(2+)when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg(2+). Recoveries were 90-110% for both species.     

Vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction

A novel sample pre-treatment technique, based on vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction (VSLLME), followed by gas chromatography-flame photometric detection (GC-FPD) has been developed for the determination of seven organophosphorus pesticides (OPPs) in wine and honey samples. In the VSLLME method, the extraction solvent was dispersed into the aqueous samples by the assistance of vortex agitator. Meanwhile, the addition of a surfactant, which was used as an emulsifier, could enhance the speed of the mass-transfer from aqueous samples to the extraction solvent. The main parameters relevant to this method were investigated and the optimum conditions were established: 15 μL chlorobenzene was used as extraction solvent, 0.2 mmol L(-1) Triton X-114 was selected as the surfactant, the extraction time was fixed at 30s, 3% sodium chloride was added and the extraction process was performed under the room temperature. Under the optimum conditions, limits of detections (LODs) were varied between 0.01 and 0.05 μg L(-1). The relative standard deviation (RSD, n=6) ranged from 2.3% and 8.9%. The linearity was obtained by five points in the concentration range of 0.1-50.0 μg L(-1). Correlation coefficients (r) varied from 0.9969 to 0.9991. The enrichment factors (EFs) were in a range of 282-309. Finally, the proposed method has been successfully applied to the determination of target analytes in real samples. The recoveries of the target analytes in wine and honey samples were between 81.2% and 108.0%.     

Determination of anti‐malaria agent chloroquine using single drop liquid‐liquid‐liquid microextraction

A simple, sensitive, and inexpensive single drop liquid‐liquid‐liquid microextraction combined with isocratic RP‐HPLC and UV detection was developed for the determination of anti‐malaria drug, chloroquine. The target compound was extracted from alkaline aqueous sample solution (adjusted to 0.5 mol/L sodium hydroxide) through a thin layer of organic solvent membrane and back‐extracted to an acidic acceptor drop (adjusted to 0.02 mol/L phosphoric acid) suspended on the tip of a 25 μL HPLC syringe in the organic layer. This syringe was also used for direct injection after extraction. The linear range was 1–200 μg/L. The LOD and LOQ were 0.3 and 1.0 μg/L, respectively. Intra‐and inter‐day precisions were less than 2.0 and 2.3%, respectively. The real samples were successfully analyzed using the proposed method. The recoveries of spiked samples were more than 94.6%.     

Novel Microporous Membrane/Solvent Microextraction for Preconcentration of Cinnamic Acid Derivatives in Rhizoma Typhonii

A novel microporous membrane/solvent microextraction (MPMSME) approach was developed in which a piece of microporous filter membrane was used as not only extraction solvent holder but also solid phase extraction unit. Subsequently, high-performance liquid chromatography with an UV detector was conducted. The wide exchange surface and very little organic solvent consumption made this sample pretreatment technology very interesting. The cinnamic acid derivatives were used as model analytes to evaluate the procedure. Parameters that affect the MPMSME such as type of extraction solvent, membrane area (or volumes of extraction solvent), aqueous phase pH, ionic strength, extraction stirring rate, extraction time, and sample volume were investigated and optimized. The enrichment factor (EF) of analyte was defined in MPMSME. Under the optimized conditions, the EFs of cinnamic acid derivatives were 43–144. Good linearities were obtained from 4 to 4,000 ng mL^?1 for all the analytes with regression coefficients of between 0.9956 and 0.9977; the limits of quantification were below 0.4 ng mL^?1, and satisfactory recoveries (93–106 %) and precisions (0.37–13 %) were also achieved. The experimental results showed that the method was simple, rapid, practical, and effective for preconcentration and determination of the cinnamic acid derivatives in rhizoma typhonii.     

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.     

Preliminary appraisal of a novel sampling and storage technique for the speciation analysis of lead and mercury in seawater

A sampling technique suitable for the preconcentration of lead and mercury species from seawater was developed and evaluated in this preliminary study. Seawater was first pumped through a tubular functional membrane at a flow rate of 2 ml min^–1 for adjustment of the sample pH. The analyte species were then enriched by solid-phase extraction in a microcolumn containing a resin with immobilized dithiocarbamate (DTC) groups. Optimum recoveries of alkyl- and inorganic lead species were obtained at a pH of about 7, whereas the enrichment efficiencies of alkyl- and inorganic mercury compounds were fairly independent of pH. The buffering membrane was effective in adjusting the pH of the seawater stream from its natural value of 8.1 to 7.1 prior to analyte enrichment on the DTC resin. Storage stability of the analyte species on the column was also studied, but found to be poor, indicating that elution from the DTC resin and further sample processing should commence as soon as possible after loading. Suggestions for further development and improvement of the proposed sampling technique are given.     

Potential of combining of liquid membranes and molecularly imprinted polymers in extraction of 17β‐estradiol from aqueous samples

The potential of combination of liquid membranes (microporous membrane liquid–liquid extraction) and molecularly imprinted polymers (MIPs) was performed using 17β‐estradiol (E2) as model compound. The model compound was extracted from aqueous sample through a hydrophobic porous membrane that was impregnated with hexane/ethyl acetate (3:2), which also formed part of the acceptor phase. In the acceptor phase, the compound was bound onto MIP particles that were also part of the organic phase. The potential of such combination was optimised for the type and amount of MIP particles in the organic acceptor phase, the extraction time, and the type of organic acceptor solvent. Ultrasound assisted binding of E2 onto MIP particles was also investigated. MIPs prepared by precipitation polymerization were found to be superior to those prepared by bulk polymerization. Increase in the extraction time and the amount of MIP particles in the acceptor phase led to more E2 binding onto the MIP particles. Hexane/ethyl acetate (3:2) as an organic acceptor was found to give higher E2 binding onto MIP particles compared to toluene, diethyl ether, and hexane. Ultrasound was furthermore found to increase the binding of E2 onto MIP particles. The selectivity of the technique was demonstrated by extracting wastewater and where clean chromatograms were obtained compared to liquid membrane extractions (SLMs) alone.