Dispersive liquid–liquid microextraction and spectrophotometric determination of cobalt in water samples

A new simple and rapid dispersive liquid–liquid microextraction has been applied to preconcentrate trace levels of cobalt as a prior step to its determination by spectrophotometric detection. In this method a small amount of chloroform as the extraction solvent was dissolved in pure ethanol as the disperser solvent, then the binary solution was rapidly injected by a syringe into the water sample containing cobalt ions complexed by 1-(2-pyridylazo)-2-naphthol (PAN). This forms a cloudy solution. The cloudy state was the result of chloroform fine droplets formation, which has been dispersed in bulk aqueous sample. Therefore, Co-PAN complex was extracted into the fine chloroform droplets. After centrifugation (2 min at 5000 rpm) these droplets were sedimented at the bottom of conical test tube (about 100 µL) and then the whole of complex enriched extracted phase was determined by a spectrophotometer at 577 nm. Complex formation and extraction are usually affected by some parameters, such as the types and volumes of extraction solvent and disperser solvent, salt effect, pH and the concentration of chelating agent, which have been optimised for the presented method. Under optimum conditions, the enhancement factor (as the ratio of slope of preconcentrated sample to that obtained without preconcentration) of 125 was obtained from 50 mL of water sample, and the limit of detection (LOD) of the method was 0.5 µg L^?1and the relative standard deviation (RSD, n = 5) for 50 µg L^?1 of cobalt was 2.5%. The method was applied to the determination of cobalt in tap and river water samples.     

Optimization of Pretreatment Method for Alkylmercuries Speciation in Coal by High‐Performance Liquid Chromatography Coupled with UV‐Digestion Cold Vapor Atomic Fluorescence Spectrometry

Abstract

Exhaustive extraction of analytes in their original chemical forms from samples with complex matrices is a pivotal step for speciation analysis. Herein we propose a pretreatment method for extracting and preconcentrating methylmercury and ethylmercury from coal samples by using KBr–H₂SO₄/CuSO₄–C₆H₅CH₃–Na₂S₂O₃ system. The extraction conditions, including the volume of the organic phase and the extraction time, were optimized in detail. Speciation analysis of alkylmercuries was carried out by high‐performance liquid chromatography online coupled with UV‐digestion and cold vapor atomic fluorescence spectrometry. The detection limits were 0.6 ng mL^?1 for methylmercury and 1 ng mL^?1 for ethylmercury, respectively. The recoveries of methylmercury and ethylmercury spiked in a sample were 84% and 82%, respectively. The method was applied successfully to analysis of alkylmercuries in four coal samples collected from northeast China.     

Microextraction techniques for the determination of volatile and semivolatile organic compounds from plants: A review

Vegetables and fruits are necessary for human health, and traditional Chinese medicine that uses plant materials can cure diseases. Thus, understanding the composition of plant matrix has gained increased attention in recent years. Since plant matrix is very complex, the extraction, separation and quantitation of these chemicals are challenging.     

Sensitive detection of drug vapors using an ion funnel interface for secondary electrospray ionization mass spectrometry

In this study, we use an ion funnel (IF) at ambient pressure to enhance the sensitivity of secondary electrospray ionization (SESI). Atenolol, salbutamol and cocaine as test compounds are delivered to the SESI interface in the gas phase and are charged with three nano electrosprays. In our experiments, we show that the compounds can be detected at concentrations in the low pptv range, which is an increase of two orders of magnitude compared with the results without the IF. With a standard SESI interface, the compounds could not be detected at all. With the use of the SESI IF interface for the headspace analysis of bananas and limes, we can detect many more compounds and at higher intensities than with a standard SESI interface. Copyright © 2012 John Wiley & Sons, Ltd.     

Ultrasound-assisted extraction of antimony and cobalt from inorganic environmental samples using a cup-horn sonoreactor prior to their determination by electrothermal-atomic absorption spectrometry

A simple, fast and reliable method is described for the quantitative extraction of Sb and Co from inorganic environmental matrices containing variable amounts of silicates prior to their determination by electrothermal-atomic absorption spectrometry. The method is based on the ultrasound-assisted extraction of both elements using the mixture 20% v/v HF + 20% v/v HNO₃ as extractant. The extraction procedure was carried out in closed Eppendorf vials immersed in a cup-horn sonoreactor for 20?min. Once extraction has been accomplished, the supernatant liquid is separated from the solid phase and subsequently transferred into the autosampler of the instrument. A two-level full factorial design (2⁴) was applied for screening optimisation of the variables influencing the ultrasonic extraction. These variables were: sonication time; amplitude of the ultrasound energy; nitric and hydrofluoric acid concentrations. MLDs were 0.20 and 0.06?µg?·?g^?1 for Sb and Co, respectively. Between-batch precision values, expressed as relative standard deviations (n?=?3), were less than 5.5 and 9.6% for Sb and Co, respectively. The method was evaluated using a wide variety of inorganic certified reference materials, such as SRM 2702 (Marine Sediment), SRM 2782 (Industrial Sludge), BCR 176R (Fly Ash), SRM 1633b (Coal Fly Ash) SRM 2710 (Montana Soil) and SRM 2711 (Montana Soil).     

Assessment of dispersive liquid–liquid microextraction for the simultaneous extraction,preconcentration, and derivatization of Hg2+ and CH3Hg+ for further determination by GC–MS

This work reports the development of a dispersive liquid – liquid microextraction method for the simultaneous extraction, preconcentration, and derivatization of Hg²⁺ and CH₃Hg⁺ species from water samples for further determination by GC – MS. Some parameters of the proposed method, such as volume and type of disperser and extraction solvent, and Na[B(C₆H₅)₄] concentration were investigated using response surface methodology. Suitable recoveries were obtained using 80 μL C₂Cl₄ (as extraction solvent), 1000 μL ethanol (as disperser solvent), and 300 μL 2.1 mmol/L Na[B(C₆H₅)₄] (as derivatizing agent). Accuracy was evaluated in terms of recovery and ranged from 87 to 99% with RSD values <7%. In addition, a certified reference material of water (NIST 1641d) was analyzed and agreed with the certified value about 107% (for Hg²⁺), with RSD values <8.5%. LODs were 0.3 and 0.2 μg/L, with enrichment factors of 112 and 115 for Hg²⁺ and CH₃Hg⁺, respectively. The optimized method was applied for the determination of Hg²⁺ and CH₃Hg⁺ in tap, well, and lake water samples.     

Electropolymerization of single‐walled carbon nanotubes composited with polypyrrole as a solid‐phase microextraction fiber for the detection of acrylamide in food samples using GC with electron‐capture detection

We developed a solid‐phase microextraction coupled to GC with electron‐capture detection method for the detection of acrylamide in food samples. Single‐walled carbon nanotubes and polypyrrole were electropolymerized onto a stainless‐steel wire as a coating, which possessed a homogeneous, porous, and wrinkled surface, chemical and mechanical stability, long lifespan (over 300 extractions), and good extraction efficiency for acrylamide. The linearity range between the signal intensity and the acrylamide concentration was found to be in the range 0.001–1 μg/mL, and the coefficient of determination was 0.9985. The LOD, defined as three times the baseline noise, was 0.26 ng/mL. The reproducibility for each single fiber (n = 6) and the fiber‐to‐fiber (n = 5) repeatability prepared in the same batch were less than 4.1 and 11.2%, respectively.     

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

A method was developed for the rapid separation of catecholamines by nonaqueous microchip electrophoresis (NAMCE) with LIF detection, A homemade pump‐free negative pressure sampling device was used for rapid bias‐free sampling in NAMCE, the injection time was 0.5 s and the electrophoresis separation conditions were optimized. Under the optimized conditions, the samples were separated completely in <1 min. The average migration times of the epinephrine (E), dopamine (DA), and norepinephrine (NE) were 34.26, 43.81, and 50.07 s, with an RSD of 1.05, 1.26, and 0.89% (n = 7), respectively. The linearity of the method ranged from 0.0125 to 2.0 mg/L for E and 0.025～4.0 mg/L for DA and NE, with correlation coefficients ranging between 0.9978 and 0.9986. The detection limits of E, DA, and NE were 2.5, 5.0, and 5.0 μg/L, respectively. The recoveries of E, DA, and NE in spiked urine samples were between 86 and 103%, with RSDs of 4.5～6.8% (n = 5). The proposed NAMCE with LIF detection combined with a pump‐free negative pressure sampling device is a simple, inexpensive, energy efficient, miniaturized system that can be successfully applied for the determination of catecholamines in urine samples.     

Use of Cdse/ZnS quantum dots for sensitive detection and quantification of paraquat in water samples

Based on the highly sensitive fluorescence change of water-soluble CdSe/ZnS core-shell quantum dots (QD) by paraquat herbicide, a simple, rapid and reproducible methodology was developed to selectively determine paraquat (PQ) in water samples. The methodology enabled the use of simple pretreatment procedure based on the simple water solubilization of CdSe/ZnS QDs with hydrophilic heterobifunctional thiol ligands, such as 3-mercaptopropionic acid (3-MPA), using microwave irradiation. The resulting water-soluble QDs exhibit a strong fluorescence emission at 596 nm with a high and reproducible photostability. The proposed analytical method thus satisfies the need for a simple, sensible and rapid methodology to determine residues of paraquat in water samples, as required by the increasingly strict regulations for health protection introduced in recent years. The sensitivity of the method, expressed as detection limits, was as low as 3.0 ng L⁻¹. The lineal range was between 10–5 × 10³ ng L⁻¹. RSD values in the range of 71–102% were obtained. The analytical applicability of proposed method was demonstrated by analyzing water samples from different procedence.     

Dispersive liquid–liquid microextraction followed by high-performance liquid chromatography for the determination of three carbamate pesticides in water samples

A simple, rapid and efficient method, dispersive liquid–liquid microextraction (DLLME) in conjunction with high-performance liquid chromatography (HPLC), has been developed for the determination of three carbamate pesticides (methomyl, carbofuran and carbaryl) in water samples. In this extraction process, a mixture of 35 µL chlorobenzene (extraction solvent) and 1.0 mL acetonitrile (disperser solvent) was rapidly injected into the 5.0 mL aqueous sample containing the analytes. After centrifuging (5 min at 4000 rpm), the fine droplets of chlorobenzene were sedimented in the bottom of the conical test tube. Sedimented phase (20 µL) was injected into the HPLC for analysis. Some important parameters, such as kind and volume of extraction and disperser solvent, extraction time and salt addition were investigated and optimised. Under the optimum extraction condition, the enrichment factors and extraction recoveries ranged from 148% to 189% and 74.2% to 94.4%, respectively. The methods yielded a linear range in the concentration from 1 to 1000 µg L^?1 for carbofuran and carbaryl, 5 to 1000 µg L^?1 for methomyl, and the limits of detection were 0.5, 0.9 and 0.1 µg L^?1, respectively. The relative standard deviations (RSD) for the extraction of 500 µg L^?1 carbamate pesticides were in the range of 1.8–4.6% (n = 6). This method could be successfully applied for the determination of carbamate pesticides in tap water, river water and rain water.