Headspace solid-phase microextraction using a dodecylsulfate-doped polypyrrole film coupled to ion mobility spectrometry for the simultaneous determination of atrazine and ametryn in soil and water samples

A simple and rapid headspace solid-phase microextraction (HS-SPME) based method is presented for the simultaneous determination of atrazine and ametryn in soil and water samples by ion mobility spectrometry (IMS). A dodecylsulfate-doped polypyrrole (PPy-DS), synthesized by electrochemical method, was applied as a laboratory-made fiber for SPME. The HS-SPME system was designed with a cooling device on the upper part of the sample vial and a circulating water bath for adjusting the sample temperature. The extraction properties of the fiber to spiked soil and water samples with atrazine and ametryn were examined, using a HS-SPME device and thermal desorption in injection port of IMS. Parameters affecting the extraction efficiency such as the volume of water added to the soil, pH effect, extraction time, extraction temperature, salt effect, desorption time, and desorption temperature were investigated. The HS-SPME-IMS method with PPy-DS fiber, provided good repeatability (RSDs < 10 %), simplicity, good sensitivity and short analysis times for spiked soil (200 ng g⁻¹) and water samples (100 and 200 ng mL⁻¹). The calibration graphs were linear in the range of 200-4000 ng g⁻¹ and 50-2800 ng mL⁻¹ for soil and water respectively (R² > 0.99). Detection limits for atrazine and ametryn were 37 ng g⁻¹ (soil) and 23 ng g⁻¹ (soil) and 15 ng mL⁻¹ (water) and 10 ng mL⁻¹ (water), respectively. To evaluate the accuracy of the proposed method, atrazine and ametryn in the three kinds of soils and two well water samples were determined. Finally, comparing the HS-SPME results for extraction and determination of selected triazines using PPy-DS fiber with the other methods in literature shows that the proposed method has comparable detection limits and RSDs and good linear ranges.     

Development and validation of a high-throughput double solid phase extraction-liquid chromatography-tandem mass spectrometry method for the determination of tetrodotoxin in human urine and plasma

A sensitive analytical method for the determination of tetrodotoxin (TTX) in urine and plasma matrices was developed using double solid phase extraction (C18 and hydrophilic interaction liquid chromatography) and subsequent analysis by HPLC coupled with tandem mass spectrometry. The double SPE sample cleanup efficiently reduced matrix and ion suppression effects. Together with the use of ion pair reagent in the mobile phase, isocratic elution became possible which enabled a shorter analysis time of 5.5 min per sample. The assay results were linear up to 500 ng mL⁻¹ for urine and 20 ng mL⁻¹ for plasma. The limit of detection and limit of quantification were 0.13 ng mL⁻¹ and 2.5 ng mL⁻¹, respectively, for both biological matrices. Recoveries were in the range of 75-81%. To eliminate the effect of dehydration and variations in urinary output, urinary creatinine-adjustment was made. TTX was quantified in eight urine samples and seven plasma samples from eight patients suspected of having TTX poisoning. TTX was detected in all urine samples, with concentrations ranging from 17.6 to 460.5 ng mL⁻¹, but was not detected in any of the plasma samples. The creatinine-adjusted TTX concentration in urine (ranging from 7.4 to 41.1 ng μmol⁻¹ creatinine) correlated well with the degree of poisoning as observed from clinical symptoms.     

Food safety evaluation: Detection and confirmation of chloramphenicol in milk by high performance liquid chromatography-tandem mass spectrometry

A simple and rapid procedure for extraction of chloramphenicol (CAP) in milk and analysis by high-performance liquid chromatography coupled with quadrupole mass spectrometry in tandem was developed. The method consisted of one step of liquid-liquid extraction using ethyl acetate and acidified water (10 mmol L⁻¹ formic acid) and HPLC-MS/MS detection. CAP-D5 was used as internal standard. The method was validated according to Commission Decision 2002/657/EC. The calibration curves were linear, with typical r² values higher than 0.98. Absolute recovery of CAP from milk proved to be more than 95%, however CAP-D5 absolute recovery was 75%. The method was accurate and reproducible, being successfully applied to the monitoring of CAP in milk samples obtained from the Brazilian market. Decision limit (CCα) was 0.05 ng mL⁻¹ and detection capability (CCβ) was 0.09 ng mL⁻¹.     

Determination of trace element in Italian virgin olive oils and their characterization according to geographical origin by statistical analysis

Multi-element analysis of organic virgin olive oils from different Italian regions was carried out by inductively coupled plasma mass spectrometry (ICP-MS) aiming at developing a reliable method in the traceability of the origin of oils. The data were processed by means of the chemiometric approach of linear discriminant analysis (LDA) that allows classifying unknown samples after checking possible differentiation of samples of known origin.An external calibration curve was build for the quantitative analysis. The calibration curves for each element were linear in the range between 0.01 and 100 ng mL⁻¹ and 0.2 to 2000 ng mL⁻¹, the correlation coefficients were ranging between 0.996 and 0.999. Results from spike and recovery experiments at levels of 30 and 65 ng mL⁻¹ were in the range of 91-119%, whereas the quantitation limits, based on 10 times standard deviation of the blank, were also in the range of 0.009-10.2 ng g⁻¹, for almost all the elements.     

An interior needle electropolymerized pyrrole-based coating for headspace solid-phase dynamic extraction

A headspace solid-phase dynamic extraction (HS-SPDE) technique was developed by the use of polypyrrole (PPy) sorbent, electropolymerized inside the surface of a needle, as a possible alternative to solid-phase microextraction (SPME). Thermal desorption was subsequently, employed to transfer the extracted analytes into the injection port of a gas chromatography-mass spectrometry (GC-MS). The PPy sorbent including polypyrrole-dodecyl sulfate (PPy-DS) was deposited on the interior surface of a stainless steel needle from the corresponding aqueous electrolyte by applying a constant deposition potential. The homogeneity and the porous surface structure of the coating were examined using the scanning electron microscopy (SEM).The developed method was applied to the trace level extraction of some polycyclic aromatic hydrocarbons (PAHs) from aqueous sample. In order to enhance the extraction efficiency and increase the partition coefficient of analytes, the stainless steel needle was cooled at 5 °C, while the sample solution was kept at 80 °C. Optimization of influential experimental conditions including the voltage of power supply, the time of PPy electrodeposition, the extraction temperature, the ionic strength and the extraction time were also investigated. The detection limits of the method under optimized conditions were in the range of 0.002-0.01 ng mL⁻¹. The relative standard deviations (R.S.D.) at a concentration level of 0.1 ng mL⁻¹ were obtained between 7.54 and 11.4% (n = 6). The calibration curves of PAHs showed linearity in the range of 0.01-10 ng mL⁻¹. The proposed method was successfully applied to the extraction of some selected PAHs from real-life water samples and the relative recoveries were higher than 90% for all the analytes.     

Development, validation and application of a method based on DI-SPME and GC-MS for determination of pesticides of different chemical groups in surface and groundwater samples

A simple and rapid method based on solid-phase micro extraction (SPME) technique followed by gas chromatography-mass spectrometry with selected ion monitoring (GC-MS, SIM) was developed by the simultaneous determination of 16 pesticides of seven different chemical groups [Six organophosphorus (trichlorfon, diazinon, methyl parathion, malathion, fenthion and ethyon), three pyrethroids (bifenhin, permethrin, cypermethrin), two imidazoles (imazalil and prochloraz), two strobilurins (azoxystrobin and pyraclostrobin), one carbamate (carbofuran), one tetrazine (clofentezine), and one triazole (difenoconazole)] in water. The pesticides extraction was done with direct immersion mode (DI-SPME) of the polyacrilate fiber (PA 85 µm). The extraction temperature was adjusted to 50 °C during 30 min, while stirring at 250 rpm was applied. After extraction, the fiber was introduced in the GC injector for thermal desorption for 5 min. at 280 °C. The method was validated using ultra pure water samples fortified with pesticides at different concentration levels and shows good linearity in the concentrations between 0.05 and 250.00 ng mL^− 1. The LOD and LOQ ranged, from 0.02 to 0.30 ng mL^− 1 and 0.05 to 1.00 ng mL^− 1, respectively. Intra-day and inter-day precisions were determined in two concentration levels (5.00 and 50.00 ng mL^− 1). Intra-day relative standard deviation (%R.S.D.) ranged between 3.6 and 13.6%, and inter-day (%R.S.D.) ranged between 6.3 and 18.5%. Relative recovery tests were carried out spiking the ultra pure sample with standards in three different concentration levels 0.20, 5.00 and 50.00 ng mL^− 1. The recovery at 0.20 ng mL^− 1 level varied from 86.4 ± 9.4% to 108.5 ± 10.5%, at 5.00 ng mL^− 1 level varied from 77.5 ± 10.8% to 104.6 ± 9.6% and at 50.00 ng mL^− 1 level varied from 70.2 ± 4.6% to 98.4 ± 8.5%. The proposed SPME method was applied in twenty-six water samples collected in the “Platô de Neópolis”, State of Sergipe, Brazil. Methyl parathion was detected in five samples with an average concentration of 0.17 ng mL^− 1 and bifenthrin, pyraclostrobin and azoxystrobin residues were found in three samples with average concentrations of 2.28, 3.12 and 0.15 ng mL^− 1, respectively.     

Electropolymerized multiwalled carbon nanotubes/polypyrrole fiber for solid-phase microextraction and its applications in the determination of pyrethroids

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes/polypyrrole (MWCNTs/Ppy) was prepared with an electrochemical method and used for the extraction of pyrethroids in natural water samples. The results showed that the MWCNTs/Ppy coated fiber had high organic stability, and remarkable acid and alkali resistance. In addition, the MWCNTs/Ppy coated fiber was more effective and superior to commercial PDMS and PDMS/DVD fibers in extracting pyrethroids in natural water samples. Under optimized conditions, the calibration curves were found to be linear from 0.001 to 10 μg mL⁻¹ for five of the six pyrethroids studied, the exception being fenvalerate (which was from 0.005 to 10 μg mL⁻¹), and detection limits were within the range 0.12-0.43 ng mL⁻¹. The recoveries of the pyrethroids spiked in water samples at 10 ng mL⁻¹ ranged from 83 to 112%.     

Determination of the antidepressant mirtazapine and its two main metabolites in human plasma by liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method for the determination in human plasma of the recent noradrenergic and specific serotonergic antidepressant (NaSSA) mirtazapine and its two main metabolites, N-desmethylmirtazapine and 8-hydroxymirtazapine, has been developed. Fluorescence detection was used, exciting at λ = 290 nm and monitoring emission at λ = 370 nm. Separation was obtained by using a reversed-phase column (C8, 250 mm × 4.6 mm I.D., 5 μm) and a mobile phase composed of 75% aqueous phosphate buffer containing triethylamine at pH 3.0 and 25% acetonitrile. Melatonin was used as the internal standard. A careful pre-treatment of plasma samples was developed, using solid-phase extraction with phenyl cartridges (100 mg, 1 mL). The calibration curves were linear over a working range of 5-150 ng mL⁻¹ for mirtazapine and of 2.5-75.0 ng mL⁻¹ for N-desmethylmirtazapine and 8-hydroxymirtazapine. The limit of quantitation (LOQ) was 2.5 ng mL⁻¹ and the limit of detection (LOD) was 1.25 ng mL⁻¹ for all analytes. The method was applied with success to plasma samples from depressed patients undergoing treatment with mirtazapine. Precision data, as well as accuracy results, were satisfactory and no interference from other drugs was found. Hence the method is suitable for therapeutic drug monitoring of mirtazapine and its metabolites in depressed patients’ plasma.     

Development of an ICP-MS immunoassay for the detection of anti-erythropoietin antibodies

A sandwich-type immunoassay linked with inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the detection of anti-erythropoietin antibodies (anti-EPO Abs). Recombinant human erythropoietin (rhEPO) was immobilized on the solid phase to capture anti-rhEPO Abs specifically. After the immunoreactions with Au-labeled goat-anti-rabbit IgG, a diluted HNO₃ (2%) was used to dissociate Au nanoparticles which was then introduced to the ICP-MS for measurements. Under the optimized conditions, the calibration graph for anti-EPO Abs was linear in the range of 35.6-500 ng mL⁻¹ with a detection limit of 10.7 ng mL⁻¹ (3σ, n = 9). The relative standard deviation (R.S.D.) for three replicate measurements of 30.9 ng mL⁻¹ of anti-EPO Abs was 8.43%. The recoveries of anti-EPO Abs in sera at the spiking level of 50, 100, 150, 200 and 400 ng mL⁻¹ were 99.2%, 101.5%, 95.0%, 94.0% and 102.9%, respectively. For the real sample analysis, 26 samples from healthy people and 53 samples from patients with rhEPO treatments were studied. One sample from patients showed significantly higher anti-EPO Abs from other samples, indicating a possibility of immune response of this patient.     

Chromatographic analysis of serotonin, 5-hydroxyindolacetic acid and homovanillic acid in dried blood spots and platelet poor and rich plasma samples

An isocratic high-performance liquid chromatographic method has been developed for the measurement of serotonin, 5-hydroxyindolacetic and homovanillic acids in dried blood spots and in platelet poor and rich plasma samples. Analyses were carried out on a C18 reversed-phase column using a mobile phase composed of 13% methanol and 87% aqueous citrate buffer, containing octanesulfonic and ethylendiaminotetracetic acids. Coulometric detection was used, setting the guard cell at +0.100 V, the first analytical cell at −0.200 V and the second analytical cell at +0.400 V. For the pre-treatment of biological samples a novel solid-phase extraction procedure, based on mixed-mode reversed-phase – strong anion exchange Oasis cartridges, was implemented. Extraction yields of the analytes from all these matrices were satisfactory, being always higher than 89.0%. The calibration curve was linear over the on-column concentration range of 0.1–22.5 ng mL⁻¹ for serotonin and 5-hydroxyindolacetic acid and of 0.25–22.5 ng mL⁻¹ for homovanillic acid. The sensitivity was good with a limit of detection of 0.05 ng mL⁻¹ for serotonin and 5-hydroxyindolacetic acid and 0.12 ng mL⁻¹ for homovanillic acid. Results were also satisfactory in terms of precision, selectivity and accuracy. The analytical method was successfully applied to human platelet poor and rich plasma samples and to dried blood spots from volunteers and psychiatric patients.     

Determination of perfluorooctanoic acid and perfluorooctane sulfonate by automated in-tube solid-phase microextraction coupled with liquid chromatography-mass spectrometry

We have developed a simple, rapid, and sensitive method for the determination of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) by on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography-mass spectrometry (LC-MS). PFOA and PFOS were separated within 10 min by high-performance liquid chromatography using an Inertsil ODS-3 column and 10 mM ammonium acetate/methanol (35/65, v/v) as a mobile phase at a flow rate of 0.25 mL min⁻¹. Electrospray ionization conditions in the negative ion mode were optimized for MS detection of PFOA and PFOS. The optimum in-tube SPME conditions were 20 draw/eject cycles with a sample size of 40 μL using a CP-Pora PLOT amine capillary column as the extraction device. The extracted compounds could be desorbed easily from the capillary by passage of the mobile phase, and no carryover was observed. Using the in-tube SPME LC-MS method, good linearity of the calibration curve (r = 0.9990 for PFOA, r = 0.9982 for PFOS) was obtained in the range of 0.05-5 ng mL⁻¹ each compound. The detection limits (S/N = 3) for PFOA and PFOS were 1.5 and 3.2 pg mL⁻¹, respectively. The method described here showed about 100-fold higher sensitivity than the direct injection method. The within-day and between-day precisions (relative standard deviations) were below 3.7 and 6.0%, respectively. This method was applied successfully to the analysis of PFOA and PFOS in environmental water samples and to the elution test from a Teflon^®-coated frying pan without interference peaks. The recoveries of PFOA and PFOS spiked into river samples were above 81%, and PFOA was detected at pg mL⁻¹ levels in environmental water samples and eluate from the frying pan.     

Determination of dimethylselenide and dimethyldiselenide in milk and milk by-products by solid-phase microextraction and gas chromatography with atomic emission detection

A method based on solid-phase microextraction (SPME) followed by gas chromatography with microwave-induced plasma atomic emission detection for determining dimethylselenide (DMSe) and dimethyldiselenide (DMDSe) in milk and milk by-products is proposed. Parameters affecting the SPME, such as sample volume or mass, ionic strength, adsorption and desorption times and temperatures were optimized in the headspace mode. The matrix effect was evaluated for the different samples studied, concluding that standard additions calibration was required for quantification purposes. The detection limits ranged from 70 to 110 pg mL⁻¹ for DMSe and from 80 to 400 pg mL⁻¹ for DMDSe, depending on the sample under analysis. None of the twenty-three samples analyzed contained the studied compounds at concentrations above the corresponding detection limits.     

CoFe2O4 nano-particles functionalized with 8-hydroxyquinoline for dispersive solid-phase micro-extraction and direct fluorometric monitoring of aluminum in human serum and water samples

A simple dispersive solid-phase micro-extraction method based on CoFe₂O₄ nano-particles (NPs) functionalized with 8-hydroxyquinoline (8-HQ) with the aid of sodium dodecyl sulfate (SDS) was developed for separation of Al(III) ions from aqueous solutions. Al(III) ions are separated at pH 7 via complex formation with 8-HQ using the functionalized CoFe₂O₄ nano-particles sol solution as a dispersed solid-phase extractor. The separated analyte is directly quantified by a spectrofluorometric method at 370 nm excitation and 506 nm emission wavelengths. A comparison of the fluorescence of Al(III)–8-HQ complex in bulk solution and that of Al(III) ion interacted with 8-HQ/SDS/CoFe₂O₄ NPs revealed a nearly 5-fold improvement in intensity. The experimental factors influencing the separation and in situ monitoring of the analyte were optimized. Under these conditions, the calibration graph was linear in the range of 0.1–300 ng mL⁻¹ with a correlation coefficient of 0.9986. The limit of detection and limit of quantification were 0.03 ng mL⁻¹ and 0.10 ng mL⁻¹, respectively. The inter-day and intra-day relative standard deviations for six replicate determinations of 150 ng mL⁻¹ Al(III) ion were 2.8% and 1.7%, respectively. The method was successfully applied to direct determine Al(III) ion in various human serum and water samples.     

A new high-performance liquid chromatography assay for the determination of sesquiterpene lactone 15-deoxygoyazensolide in rat plasma

A simple, rapid and sensitive high-performance liquid chromatography method was developed for the analysis of the sesquiterpene lactone 15-deoxygoyazensolide (LAC15-D) in rat plasma samples. The chromatographic separation was achieved on a LiChrospher^® RP18 column using methanol:water (50:50, v/v) containing 0.6% acetic acid as mobile phase, at a flow rate of 0.7 mL min⁻¹. UV detection was carried out at 270 nm. Phenytoin was used as internal standard. Prior to the analysis, the rat plasma samples were submitted to liquid-liquid extraction with dichloromethane. The mean absolute recoveries were 73% with R.S.D. values lower than 3.5. The method was linear over the 6.0-2000 ng mL⁻¹ concentration range and the quantification limit was 6.0 ng mL⁻¹. Within-day and between-day assay precision and accuracy were studied at three concentration levels (15, 300 and 480 ng mL⁻¹) and were lower than 15%. The validated method was used to measure the plasmatic concentration of LAC15-D in rats that received a single intraperitoneal dose of 30 mg kg⁻¹.     

Development of an extraction method for the determination of prostaglandins in biological tissue samples using liquid chromatography–tandem mass spectrometry: Application to gonads of Atlantic cod (Gadus morhua)

A simple extraction method for the analysis of PGE₂ and PGF_2α in gonad samples from Atlantic cod and further quantification by using liquid chromatography–tandem mass spectrometry is proposed. The evaluation of the best solvent extraction conditions and the analytical performance parameters are reported. The method was highly selective for both prostaglandins and the calibration curves, based on the internal standard method, were linear between 5 and 1000 ng mL⁻¹ for PGE₂ and PGF_2α, with limits of detection of 1 ng mL⁻¹ and 1.5 ng mL⁻¹ and recovery values of 99.999 ± 0.002 and 99.967 ± 0.023 respectively. The homogenization of samples using liquid nitrogen combined with the developed extraction protocol can be implemented in different types of biological tissues.     

High-performance liquid chromatographic analysis of amphotericin B in rat plasma using α-naphthol as an internal standard

A simple, sensitive and accurate reverse phase high-performance liquid chromatographic (RP-HPLC) method with photo-diode array detector (PDA) was developed and validated for the determination of amphotericin B (AMB) in the rat plasma using a new internal standard (IS) α-naphthol. The plasma samples were subjected to protein precipitation with methanol prior to a HPLC analysis. Chromatographic separations were achieved on a Nucleosil^® 100-5C18 (150 mm × 4.6 mm) column. The mobile phase consisted of acetonitrile and sodium acetate buffer (pH 4; 10 mM) in a gradient mode. Detection was carried out at a wavelength of 407 and 294 nm for AMB and IS, respectively. The retention times of AMB and IS were about 6.8 and 7.8 min, respectively. The calibration curve was linear in the range of 10-2000 ng mL⁻¹ for AMB (r² > 0.998). No significant matrix effect was observed on quantification of AMB or IS. At three quality control concentrations of 20, 500, and 2000 ng mL⁻¹, the intra-day and inter-day relative standard deviation ranged from 1.13% to 4.91%. The limit of detection (LOD) was 5 ng mL⁻¹ and the limit of quantification (LOQ) was 10 ng mL⁻¹ for AMB in rat plasma. This method is simple, sensitive, rapid and does not require any extensive sample purification before injecting into HPLC.     

Analysis of regulated suspected allergens in waters

Fragrance suspected allergens including those regulated by the EU Directive 76/768/EEC have been determined in different types of waters using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The procedure was based on headspace sampling (HS-SPME) using polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibers and has been optimized by an experimental design approach. The method performance has been studied showing good linearity (R ≥ 0.994) as well as good intra-day and inter-day precision (RSD ≤ 12%). Detection limits (S/N = 3) ranged from 0.001 to 0.3 ng mL⁻¹. Reliability was demonstrated through the quantitative recoveries of the compounds in real water samples, including baby bathwaters, swimming pool waters, and wastewaters. The absence of matrix effects allowed quantification of the compounds by external aqueous calibration. The analysis of 35 samples of different types of waters showed the presence of suspected allergens in all the analyzed samples. All targets were found in the samples, with the exception of methyl eugenol and amyl cinnamic alcohol. Highest concentrations of suspected allergens were present in baby bathwaters, containing from 5 to 15 of the compounds at concentrations ranging from few pg mL⁻¹ to several hundreds of ng mL⁻¹.     

Ligandless-solidified floating organic drop microextraction method for the preconcentration of trace amount of cadmium in water samples

In this article, a new ligandless solidified floating organic drop microextraction (LL-SFODME) method has been developed for preconcentration of trace amount of cadmium as a prior step to its determination by flow injection-flame atomic absorption spectrometry (FI-FAAS). The methodology is based on the SFODME of cadmium with 1-dodecanol in the absence of chelating agent. Several factors affecting the microextraction efficiency, such as, pH, sodium dodecylbenzenesulfonate (SDBS) concentration, extraction time, stirring rate and temperature were investigated and optimized. Under optimized experimental conditions an enhancement factor of 205 was obtained for 100 mL of sample solution. The calibration graph was linear in the range of 1.0-25.0 ng mL⁻¹, the limit of detection (3s) was 0.21 ng mL⁻¹ and the limit of quantification (10s) was 0.62 ng mL⁻¹. The relative standard deviation (RSD) for 10 replicate measurements of 10 ng mL⁻¹ cadmium was 4.7%. The developed method was successfully applied to the extraction and determination of cadmium in standard and several water samples and satisfactory results were obtained.     

Silica gel-polyethylene glycol as a new adsorbent for solid phase extraction of cobalt and nickel and determination by flame atomic absorption spectrometry

In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0 ng mL⁻¹ for Co(II) and 2.0-100.0 ng mL⁻¹ for Ni(II) in the initial solution. The limit of detection based on 3S_b was 0.37 ng mL⁻¹ for Co(II) and 0.71 ng mL⁻¹ for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40 ng mL⁻¹ of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.     

High extraction efficiency for polar aromatic compounds in natural water samples using multiwalled carbon nanotubes/Nafion solid-phase microextraction coating

A novel solid-phase microextraction (SPME) fiber coated with multiwalled carbon nanotubes (MWCNTs)/Nafion was developed and applied for the extraction of polar aromatic compounds (PACs) in natural water samples. The characteristics and the application of this fiber were investigated. Electron microscope photographs indicated that the MWCNTs/Nafion coating with average thickness of 12.5 μm was homogeneous and porous. The MWCNTs/Nafion coated fiber exhibited higher extraction efficiency towards polar aromatic compounds compared to an 85 μm commercial PA fiber. SPME experimental conditions, such as fiber coating, extraction time, stirring rate, desorption temperature and desorption time, were optimized in order to improve the extraction efficiency. The calibration curves were linear from 0.01 to 10 μg mL⁻¹ for five PACs studied except p-nitroaniline (from 0.005 to 10 μg mL⁻¹) and m-cresol (from 0.001 to 10 μg mL⁻¹), and detection limits were within the range of 0.03–0.57 ng mL⁻¹. Single fiber and fiber-to-fiber reproducibility were less than 7.5 (n = 7) and 10.0% (n = 5), respectively. The recovery of the PACs spiked in natural water samples at 1 μg mL⁻¹ ranged from 83.3 to 106.0%.