Extraction of pesticides in water samples using vortex-assisted liquid–liquid microextraction

A simple solvent microextraction method termed vortex-assisted liquid–liquid microextraction (VALLME) coupled with gas chromatography micro electron-capture detector (GC-μECD) has been developed and used for the pesticide residue analysis in water samples. In the VALLME method, aliquots of 30 μL toluene used as extraction solvent were directly injected into a 25 mL volumetric flask containing the water sample. The extraction solvent was dispersed into the water phase under vigorously shaking with the vortex. The parameters affecting the extraction efficiency of the proposed VALLME such as extraction solvent, vortex time, volumes of extraction solvent and salt addition were investigated. Under the optimum condition, enrichment factors (EFs) in a range of 835–1115 and limits of detection below 0.010 μg L⁻¹ were obtained for the determination of target pesticides in water. The calculated calibration curves provide high levels of linearity yielding correlation coefficients (r²) greater than 0.9958 with the concentration level ranged from 0.05 to 2.5 μg L⁻¹. Finally, the proposed method has been successfully applied to the determination of pesticides from real water samples and acceptable recoveries over the range of 72–106.3% were obtained.     

Headspace liquid-phase microextraction of trihalomethanes in drinking water and their gas chromatographic determination

In the present work, a novel method for the determination of trihalomethanes (THMs) such as chloroform, dichlorobromomethane, chlorodibromomethane and bromoform in drinking water has been described. It is based on coupling headspace liquid-phase microextraction (HS-LPME) with gas chromatography-electron capture detector (GC-ECD). A microdrop of organic solvent at the tip of a commercial microsyringe was used to extract analytes from aqueous samples. Three organic solvents—xylene, ethylene glycol and 1-octanol—were compared and 1-octanol was the most sensitive solvent for the analytes. Extraction conditions such as headspace volume, extraction time, stirring rate, content of NaCl and extraction temperature were found to have significant influence on extraction efficiency. The optimized conditions were 15 ml headspace volume in a 40 ml vial, 10 min extraction time and 800 rpm stirring rate at 20 °C with 0.3 g ml⁻¹ NaCl. The linear range was 1-100 μg l⁻¹ for THMs. The limits of detection (LODs) ranged from 0.15 μg l⁻¹ (for dichlorobromomethane and chlorodibromomethane) to 0.4 μg l⁻¹ (for chloroform); and relative standard deviations (RSD) for most of THMs at the 10 μg l⁻¹ level were below 10%. Real samples collected from tap water and well water were successfully analyzed using the proposed method. The recovery of spiked water samples was from 101 to 112%.     

A novel microextraction technique based on 1-hexylpyridinium hexafluorophosphate ionic liquid for the preconcentration of zinc in water and milk samples

A simple dispersive liquid-liquid microextraction methodology based on the application of 1-hexylpyridinium hexafluorophosphate [HPy][PF₆] ionic liquid (IL) as an extractant solvent was proposed for the preconcentration of trace levels of zinc as a prior step to determination by flame atomic absorption spectrometry (FAAS). Zinc was complexed with 8-hydroxyquinoline (oxine) and extracted into ionic liquid. Some effective factors that influence the microextraction efficiency such as pH, oxine concentration, amount of IL, ionic strength, temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and the enhancement factor were 0.22 μg L⁻¹ and 71, respectively. The relative standard deviation (RSD) for six replicate determinations of 13 μg L⁻¹ Zn was 1.92%. In order to validate the developed method, a certified reference material (NIST SRM 1549) was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the trace determination of zinc in water and milk samples.     

Attachment of nickel hexacyanoferrates nanoparticles on carbon nanotubes: preparation, characterization and bioapplication

Anilinemethyltriethoxysilane (AMTEOS) was first used as precursor as well as selective stationary phase to prepare the sol-gel derived anilinemethyltriethoxysilane/polydimethylsiloxane (AMTEOS/PDMS) solid-phase microextraction (SPME) fibers. The novel SPME fiber exhibits high extraction efficiency, good thermal stability and long lifetime compared with commercial SPME coatings. In addition, the phenyl groups in the porous layer can exhibit π-π interactions with aromatic compounds, such as monocyclic aromatic hydrocarbons (MAHs) and polycyclic aromatic hydrocarbons (PAHs). Therefore, SPME using the AMTEOS/PDMS sol-gel fiber coupled with GC-FID was recommended as a sensitive and selective method towards the analysis of these compounds in environmental water samples. The optimal extraction conditions were investigated by adjusting extraction time, salt addition, extraction temperature, and desorption time. The method showed linearity between 2 and 4000 μg l⁻¹ for MAHs and 1 and 1000 μg l⁻¹ for PAHs. The limit of detection (LOD) was 0.6-3.8 μg l⁻¹for MAHs and 0.2-1.5 μg l⁻¹ for PAHs. The novel AMTEOS/PDMS fiber was applied to extract small amount of aromatic compounds in wastewater and river water respectively. The recovery of the method was acceptable for quantitative analysis.     

Part-per-trillion determination of chlorobenzenes in water using dispersive liquid-liquid microextraction combined gas chromatography-electron capture detection

In this study, a simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined gas chromatography-electron capture detection (GC-ECD), for the determination of chlorobenzenes (CBs) in water samples, has been described. This method involves the use of an appropriate mixture of extraction solvent (9.5 μl chlorobenzene) and disperser solvent (0.50 ml acetone) for the formation of cloudy solution in 5.00 ml aqueous sample containing analytes. After extraction, phase separation was performed by centrifugation and the enriched analytes in sedimented phase were determined by gas chromatography-electron capture detection (GC-ECD). Our simple conditions were conducted at room temperature with no stiring and no salt addition in order to minimize sample preparation steps. Parameters such as the kind and volume of extraction solvent, the kind and volume of disperser solvent, extraction time and salt effect, were studied and optimized. The method exhibited enrichment factors and recoveries ranging from 711 to 813 and 71.1 to 81.3%, respectively, within very short extraction time. The linearity of the method ranged from 0.05 to 100 μg l⁻¹ for dichlorobenzene isomers (DCB), 0.002-20 μg l⁻¹ for trichlorobenzene (TCB) and tetrachlorobenzene (TeCB) isomers and from 0.001 to 4 μg l⁻¹ for pentachlorobenzene (PeCB) and hexachlorobenzene (HCB). The limit of detection was in the low μg l⁻¹ level, ranging between 0.0005 and 0.05 μg l⁻¹. The relative standard deviations (R.S.D.s) for the concentration of DCB isomers, 5.00 μg l⁻¹, TCB and TeCB isomers, 0.500 μg l⁻¹, PeCB and HCB 0.100 μg l⁻¹ in water by using the internal standard were in the range of 0.52-2.8% (n = 5) and without the internal standard were in the range of 4.6-6.0% (n = 5). The relative recoveries of spiked CBs at different levels of chlorobenzene isomers in tap, well and river water samples were 109-121%, 105-113% and 87-120%, respectively. It is concluded that this method can be successfully applied for the determination of CBs in tap, river and well water samples.     

Determination of nitroaromatic explosives in water samples by direct ultrasound-assisted dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometry

A fast, simple, inexpensive, sensitive, efficient and environmental friendly direct ultrasound-assisted dispersive liquid-liquid microextraction (DUSA-DLLME) procedure has been developed to concentrate five nitroaromatic explosives from water samples prior to quantification by gas chromatography-mass spectrometry (GC-MS). An efficient ultrasonic probe has been used to radiate directly the samples producing very fine emulsions from immiscible liquids. A D-optimal design was used for optimizing the factors and to evaluate their influential upon extraction. The optimum experimental conditions were: sample volume, 10 mL; extraction time, 60 s; cycles, 0.6 s(s⁻¹); power of ultrasound energy, 40% (70 W); and, extractant solvent (chlorobenzene) volume, 20 μL. Under the optimized experimental conditions the method presents good level of repeatability with coefficients of variation under 6% (n = 8; spiking level 10 μg L⁻¹). Calculated calibration curves gave high level of linearity with correlation coefficient values between 0.9949 and 0.9992. Limits of detection were ranged between 0.03 and 0.91 μg L⁻¹. Finally, the proposed method was applied to the analysis of two types of water samples, reservoir and effluent wastewater. The samples were previously analysed and confirmed free of target analytes. At 5 μg L⁻¹ spiking level recovery values ranged between 75 and 96% for reservoir water sample showing that the matrix had a negligible effect upon extraction. However, a noticeable matrix effect (around 50% recovery) was observed for effluent wastewater sample. In order to alleviate this matrix effect, the standard addition calibration method was used for quantitative determination. This calibration method supplied recovery values ranged between 71 and 79%. The same conclusions have been obtained from an uncertainty budget evaluation study.     

Air-assisted liquid–liquid microextraction by solidifying the floating organic droplets for the rapid determination of seven fungicide residues in juice samples

A novel air assisted liquid–liquid microextraction using the solidification of a floating organic droplet method (AALLME-SFO) was developed for the rapid and simple determination of seven fungicide residues in juice samples, using the gas chromatography with electron capture detector (GC-ECD). This method combines the advantages of AALLME and dispersive liquid–liquid microextraction based on the solidification of floating organic droplets (DLLME-SFO) for the first time. In this method, a low-density solvent with a melting point near room temperature was used as the extraction solvent, and the emulsion was rapidly formed by pulling in and pushing out the mixture of aqueous sample solution and extraction solvent for ten times repeatedly using a 10-mL glass syringe. After centrifugation, the extractant droplet could be easily collected from the top of the aqueous samples by solidifying it at a temperature lower than the melting point. Under the optimized conditions, good linearities with the correlation coefficients (γ) higher than 0.9959 were obtained and the limits of detection (LOD) varied between 0.02 and 0.25 μg L⁻¹. The proposed method was applied to determine the target fungicides in juice samples and acceptable recoveries ranged from 72.6% to 114.0% with the relative standard deviations (RSDs) of 2.3–13.0% were achieved. Compared with the conventional DLLME method, the newly proposed method will neither require a highly toxic chlorinated solvent for extraction nor an organic dispersive solvent in the application process; hence, it is more environmentally friendly.     

Headspace single drop microextraction of methylcyclopentadienyl-manganese tricarbonyl from water samples followed by gas chromatography-mass spectrometry

Headspace single drop microextraction coupled to gas chromatography-mass spectrometry yielded a simple, fast and virtually solventless analytical protocol used for the headspace analysis of aqueous samples contaminated with methylcyclopentadienyl-manganese tricarbonyl (MMT). Initially, several experimental parameters were controlled and optimized and the optimum conditions found were 2.5 μl octane microdrop exposed for 20 min to the headspace of a 10 ml aqueous sample (15 ml vial) containing 20% (w/v) NaCl and stirred at 1250 rpm. The calculated calibration curves gave a high level of linearity for MMT with correlation coefficients >0.9995 after conducting a 3-day study. The limit of detection was calculated to be 0.21 μg l⁻¹. The proposed method achieved an enrichment factor of the order of 2100 and a 53% recovery after extracting the spiked aqueous solution for 20 min under the optimized experimental conditions. The repeatability and intra-day reproducibility of the proposed method, expressed as relative standard deviation were 8.4 and 6.4%, respectively. Finally, analysis of spiked tap and wastewater samples revealed that matrix had little effect upon extraction.     

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.     

One-step in-syringe ionic liquid-based dispersive liquid–liquid microextraction

Dispersive liquid–liquid microextraction (DLLME) has been proved to be a powerful tool for the rapid sample treatment of liquid samples providing at the same time high enrichment factors and extraction recoveries. A new, simple and easy to handle one step in-syringe set-up for DLLME is presented and critically discussed in this paper. The novel approach avoids the centrifugation step, typically off-line and time consuming, opening-up a new horizon on DLLME automation. The suitability of the proposal is evaluated by means of the determination of non-steroidal anti-inflammatory drugs in urine by liquid chromatography/ultraviolet detection. In the presented approach an ionic liquid is used as extractant. The target drugs can be determined in urine within the concentration range 0.02–10 μg mL⁻¹, allowing their determination at therapeutic and toxic levels. Limits of detection were in the range from 8.3 ng mL⁻¹ (indomethacin) to 32 ng mL⁻¹ (ketoprofen). The repeatability of the proposed method expressed as RSD (n = 5) varied between 2.5% (for ketoprofen) and 8.6% (for indomethacin).     

Determination of formaldehyde in shiitake mushroom by ionic liquid-based liquid-phase microextraction coupled with liquid chromatography

Using ionic liquid as extraction solvent and 2,4-dinitrophenylhydrazine (DNPH) as derivative agent, formaldehyde in shiitake mushroom was determined by liquid-phase microextraction coupled with high-performance liquid chromatography (HPLC). Shiitake mushroom was leached with water and filtrated, then the formaldehyde in filtrate was derivatized with DNPH and extracted simultaneously into a 10 μl drop of ionic liquid suspended on the tip of the microsyringe, and finally injected into the HPLC system for determination. The proposed procedure has a detection limit of 5 μg l⁻¹ formaldehyde in extraction solution, thus the mushroom sample filtrate could be diluted with a large ratio to eliminate the influence of sample matrix. The method has a relative standard deviation of 3.5% between days for 53.5 μg l⁻¹ formaldehyde standards. High contents of formaldehyde (119-494 μg g⁻¹ wet weight), which is harmful for human beings, were detected in shiitake mushroom. Therefore, strategies must be taken to prevent the accumulation and strictly control the content of formaldehyde in shiitake mushroom.     

Headspace liquid-phase microextraction using ionic liquid as extractant for the preconcentration of dichlorodiphenyltrichloroethane and its metabolites at trace levels in water samples

A novel technique, high temperature headspace liquid-phase microextraction (HS-LPME) with room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) as extractant, was developed for the analysis of dichlorodiphenyltrichloroethane (p,p′-DDT and o,p′-DDT) and its metabolites including 4,4′-dichlorodiphenyldichloroethylene (p,p′-DDE) and 4,4′-dichlorodiphenyldichloroethane (p,p′-DDD) in water samples by high performance liquid chromatography with ultraviolet detection. The parameters such as salt content, sample pH and temperature, stirring rate, extraction time, microdrop volume, and sample volume, were found to have significant influence on the HS-LPME. The conditions optimized for extraction of target compounds were as follows: 35% NaCl (w/v), neutral pH condition, 70 °C, 800 rpm, 30 min, 10 μL [C₄MIM][PF₆], and 25 mL sample solutions. Under the optimized conditions, the linear range, detection limit (S/N = 3), and precision (R.S.D., n = 6) were 0.3-30 μg L⁻¹, 0.07 μg L⁻¹, and 8.0% for p,p′-DDD, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.1% for p,p′-DDT, 0.3-30 μg L⁻¹, 0.08 μg L⁻¹, and 7.2% for o,p′-DDT, and 0.2-30 μg L⁻¹, 0.05 μg L⁻¹, and 6.8% for p,p′-DDE, respectively. Water samples including tap water, well water, snow water, reservoir water, and wastewater were analyzed by the proposed procedure and the recoveries at 5 μg L⁻¹ spiked level were in the range of 86.8-102.6%.     

Determination of ethylphenol compounds in wine by headspace solid-phase microextraction in conjunction with gas chromatography and flame ionization detection

Headspace solid phase microextraction (HS-SPME) was investigated as a solvent-free alternative method for the extraction and determination of 4-ethylphenol (EP) and 4-ethylguaiacol (EG) in red wine by capillary gas chromatography with flame ionization detection (FID) and compared to liquid-liquid extraction.For HS-SPME, better results were obtained with saturated sodium chloride samples, at 55 °C, using a 85 μm polyacrylate fiber. An absorption time of 40 min was needed to reach the absorption equilibrium for EG. This 40-min duration corresponds to the beginning of EP equilibrium and was selected for the experiments. In these conditions, the calibration graphs were linear in the range 5-5000 μg l⁻¹ and the sensitivity was nearly the same for the two compounds. The detection limits were in the low μg l⁻¹ range. In model wine solutions, result obtained with the liquid-liquid extraction method exhibit a linear calibration between 25 and 10,000 μg l⁻¹ with a detection limit of 1 μg l⁻¹, but, the relative standard deviations of the EP and EG result in the low concentration range (<50 μg l⁻¹) are higher than those obtained by HS-SPME (15% compared to 2% for EP and 12% compared to 5% for EG). Taking into account the numerous volatile compounds in wine, HS-SPME is a rapid and valid alternative technique for use in the determination of ethylphenols at trace levels.     

Determination of aldehydes in rainwater using micro-solid-phase extraction and high-performance liquid chromatography

A simple and rapid extraction procedure was developed for determining aldehydes in rainwater samples. This extraction technique involved the use of micro-solid-phase extraction in which the sorbent was held within a polypropylene membrane envelope, followed by high-performance liquid chromatographic analysis. Aldehydes such as formaldehyde, acetaldehyde, propionaldehyde and valeraldehyde were used as model compounds. Extraction conditions were optimized. The method linearity ranged between 0.5 and 50 μg l⁻¹ with the correlation coefficient of 0.987–0.999. The relative standard deviations (RSDs) of the method ranged from 7 to 12%. Method detection limits were in the range of 0.07–0.15 μg l⁻¹, which is lower than those previously reported for solid-phase microextraction combined with gas chromatography–mass spectrometric techniques. The proposed extraction technique was used for determination of aldehydes in rainwater samples to demonstrate the applicability of the method.     

Determination of atrazine using square wave voltammetry with the Hanging Mercury Drop Electrode (HMDE)

This paper presents the optimization of instrumental and solution parameters for determination of atrazine in river waters and formulation by square wave voltammetry (SWV) using a hanging mercury drop electrode. The best sensitivity (35.2±0.4 μA ml μg⁻¹) was achieved using a frequency of 400 Hz and a medium composed of 40 mmol l⁻¹ Britton-Robinson (BR) buffer at pH 1.9. The detection limit was 2 μg l⁻¹ with a linear dynamic range between 10 and 250 μg l⁻¹. Application of the method to real samples of river waters fortified with 10 μg l⁻¹ of atrazine resulted recoveries between 92 and 116%. Additionally, good agreement was observed between results obtained by the proposed method and by HPLC for river water samples spiked with 25 μg l⁻¹ of atrazine. The determination was not affected by the presence of humic acid at concentration of 5 mg l⁻¹, indicating that interactions of the herbicide with this class of compounds are fully labile. The stability of the voltammetric signal for samples spiked with 250 μg l⁻¹ atrazine was evaluated over a period of 14 days in four samples. For two samples, no systematic variation was observed, while for the other two, a decrease of peak current between 3 and 15% occurred, suggesting that the stability is dependent on the sample nature. HPLC analyses suggest formation of deethylatrazine during the second week of storage in the samples for which the SWV peak current had the more intense decrease.     

Application of chemometric assisted dispersive liquid-liquid microextraction to the determination of personal care products in natural waters

A rapid and simple method for the determination of two phthalates and five polycyclic musks in water samples using dispersive liquid-liquid microextraction (DLLME) mated to chemometrics and coupled to GC-MS was developed. Volume of extraction (CCl₄) and disperser solvent (MeOH), pH, ionic strength, extraction time, centrifugation time as well as centrifugation speed were optimized in a 2^7-4 Plackett-Burman design. The obtained significant factors were optimized by using a central composite design (CCD) and the quadratic model between the dependent and the independent variables was built. The optimum experimental conditions of the proposed method were: 250 μL carbon tetrachloride, 0.62 mL methanol, 7.5 min centrifugation time, natural pH containing 0% (w/v) NaCl, while keeping centrifugation speed fixed at 4000 rpm.The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9970 and 0.9992. The repeatability and reproducibility of the proposed method, expressed as relative standard deviation, varied between 2.6% to 9.7% and 5.7% to 12.2%, respectively. The obtained LOD values were in the range of 8-63 ng L⁻¹.     

Speciation of mercury by ionic liquid-based single-drop microextraction combined with high-performance liquid chromatography-photodiode array detection

Room temperature ionic liquids can be considered as environmentally benign solvents with unique physicochemical properties. Ionic liquids can be used as extractant phases in SDME, being compatible with chromatographic systems. A single-drop microextraction method was developed for separation and preconcentration of mercury species (MeHg⁺, EtHg⁺, PhHg⁺ and Hg²⁺), which relies on the formation of the corresponding dithizonates and microextraction of these neutral chelates onto a microdrop of an ionic liquid. Afterwards, the separation and determination were carried out by high-performance liquid chromatography with a photodiode array detector. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were: microextraction time, 20 min; stirring rate, 900 rpm; pH, 11; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C₆MIM][PF₆]); drop volume, 4 μL; and no sodium chloride addition. Limits of detection were between 1.0 and 22.8 μg L⁻¹ for the four species of mercury, while the repeatability of the method, expressed as relative standard deviation, was between 3.7 and 11.6% (n = 8). The method was finally applied to the determination of mercury species in different water samples.     

Determination of organochlorine pesticides in water samples by dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry

A rapid and simple dispersive liquid-liquid microextraction (DLLME) has been developed to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples prior to analysis by gas chromatography-mass spectrometry (GC-MS). The studied variables were extraction solvent type and volume, disperser solvent type and volume, aqueous sample volume and temperature. The optimum experimental conditions of the proposed DLLME method were: a mixture of 10 μL tetrachloroethylene (extraction solvent) and 1 mL acetone (disperser solvent) exposed for 30 s to 10 mL of the aqueous sample at room temperature (20 °C). Centrifugation of cloudy solution was carried out at 2300 rpm for 3 min to allow phases separation. Finally, 2 μL of extractant was recovered and injected into the GC-MS instrument. Under the optimum conditions, the enrichment factors ranged between 46 and 316. The calculated calibration curves gave a high-level linearity for all target analytes with correlation coefficients ranging between 0.9967 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5% and 15% (n = 8), and the detection limits were in the range of 1-25 ng L⁻¹. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA methods 525.2 and 625. Analysis of spiked real water samples revealed that the matrix had no effect on extraction for river, surface and tap waters; however, urban wastewater sample shown a little effect for five out of eighteen analytes.     

Spectrophotometric catalytic determination of Fe(III) in estuarine waters using a flow-batch system

A flow-batch system was developed for the determination of Fe(III) in estuarine waters with high variability in salinity. The method is based on the catalytic effect of iron(III) on the oxidation rate of N,N-dimethyl-p-phenylenediammonium dichloride (DmPD) by hydrogen peroxide and the formed product is spectrophotometrically monitored at 554 nm. A controlled addition of sodium chloride to every assayed sample is accomplished for in-line individual salinity matching.The proposed system processes about 30 samples h⁻¹ and yields reproducible results. Relative standard deviations were estimated as <1.5% after 10 injections of typical samples (10.0-50.0 μg l⁻¹ Fe; ca. 0.5 mol l⁻¹ Cl). Synthetic samples (15.0 μg l⁻¹ Fe; 0.25-1.0 mol l⁻¹ NaCl) were efficiently processed, and no significant differences in results were found at a probability level of 99.7%. The method works for the full range of salinities. Only 120 μg DmPD are consumed per determination. The analytical curve is linear up to about 60 μg l⁻¹ Fe (r>0.999; n=5) and the detection limit is 5 μg l⁻¹ Fe. Results are in agreement with graphite furnace atomic absorption spectrometry.     

Analyses of polychlorinated biphenyls in waters and wastewaters using vortex-assisted liquid-liquid microextraction and gas chromatography-mass spectrometry

A method was developed for viable and rapid determination of seven polychlorinated biphenyls (PCBs) in water samples with vortex-assisted liquid-liquid microextraction (VALLME) using gas chromatography-mass spectrometry (GC-MS). At first, the most suitable extraction solvent and extraction solvent volume were determined. Later, the parameters affecting the extraction efficiency such as vortex extraction time, rotational speed of the vortex, and ionic strength of the sample were optimized by using a 2(3) factorial experimental design. The optimized extraction conditions for 5 mL water sample were as follows: extractant solvent 200 μL of chloroform; vortex extraction time of 2 min at 3000 rpm; centrifugation 5 min at 4000 rpm, and no ionic strength. Under the optimum condition, limits of detection (LOD) ranged from 0.36 to 0.73 ng/L. Mean recoveries of PCBs from fortified water samples are 96% for three different fortification levels and RSDs of the recoveries are below 5%. The developed procedure was successfully applied to the determination of PCBs in real water and wastewater samples such as tap, well, surface, bottled waters, and municipal, treated municipal, and industrial wastewaters. The performance of the proposed method was compared with traditional liquid-liquid extraction (LLE) of real water samples and the results show that efficiency of proposed method is comparable to the LLE. However, the proposed method offers several advantages, i.e. reducing sample requirement for measurement of target compounds, less solvent consumption, and reducing the costs associated with solvent purchase and waste disposal. It is also viable, rapid, and easy to use for the analyses of PCBs in water samples by using GC-MS.