Application of copolymer coated frits for solid-phase extraction of poly cyclic aromatic hydrocarbons in water samples

A conducting copolymer of pyrrole and phenol was electrochemically synthesized on steel frits as a sorbent. The applicability of the frit was assessed for the solid-phase extraction of trace amounts of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples followed by HPLC–UV. The coating produced was very adherent and the scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and FTIR spectrum for the coated frit were studied. The effects of various parameters on the efficiency of the solid-phase extraction process, such as the sample loading rate, elution solvent type, salt effect, volume and flow rate of sample and elution solvent were investigated. Under the optimal conditions, the calibration curves were obtained in the range of 0.1–500 ng mL⁻¹ (r² > 0.98) and the LODs (S/N = 3) were obtained in the range of 0.01–0.08 ng mL⁻¹. Relative standard deviations (RSDs) for intra- and inter-day precision were 2.7–10.2% and 3.6–11.4%, respectively. The recoveries (8 and 40 ng mL⁻¹) ranged from 79% to 115%. The simplicity of experimental procedure, short sample analysis, high extraction efficiency, and the use of low-cost adsorbent show the potential of this method for routine analysis of PAHs in real samples.     

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.     

Determination of 16 polycyclic aromatic hydrocarbons in environmental water samples by solid-phase extraction using multi-walled carbon nanotubes as adsorbent coupled with gas chromatography–mass spectrometry

A solid-phase extraction (SPE) using multi-walled carbon nanotubes (MWCNTs) as adsorbent coupled with gas chromatography–mass spectrometry (GC–MS) method was developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. Several condition parameters, such as extraction adsorbents, elution solvents and volumes, and sample loading flow rate and volume were optimized to obtain high SPE recoveries and extraction efficiency. 150 mg MWCNTs as sorbent presented high extraction efficiency of 16 PAHs due to the large specific surface area and high adsorption capacity of MWCNTs compared with the commercial C18 column (250 mg/2 mL). The calibration curves of 16 PAHs extracted were linear in the range of 20–5000 ng L⁻¹, with the correlation coefficients (r²) between 0.9848 and 0.9991. The method attained good precisions (relative standard deviation, RSD) from 1.2% to 12.1% for standard PAHs aqueous solutions; method recoveries ranged in 76.0–125.5%, 74.5–127.0%, and 70.0–122.0% for real spiked samples from river water, tap water and seawater, respectively. Limits of detection (LODs, S/N = 3) of the method were determined from 2.0 to 8.5 ng L⁻¹. The optimized method was successfully applied to the determination of 16 PAHs in real environmental water samples.     

At-line microextraction by packed sorbent-gas chromatography–mass spectrometry for the determination of UV filter and polycyclic musk compounds in water samples

An at-line analysis protocol is presented that allows the determination of four UV filters, two polycyclic musk compounds and caffeine in water at concentration level of ng L⁻¹. The fully automated method includes analytes enrichment by Microextraction by packed sorbent (MEPS) coupled directly to large volume injection-gas chromatography–mass spectrometry. Two common SPE phases, C8 and C18, were examined for their suitability to extract the target substances by MEPS. The analytes were extracted from small sample volumes of 800 μL with recoveries ranging from 46 to 114% for the C8-sorbent and 65–109% for the C18-sorbent. Limits of detection between 34 and 96 ng L⁻¹ enable the determination of the analytes at common environmental concentration levels. Both sorbents showed linear calibration curves for most of the analytes up to a concentration level of 20 ng mL⁻¹. Carryover was minimized by washing the sorbents 10 times with 100 μL methanol. After this thorough cleaning, the MEPS are re-used and up to 70 analyses can be performed with the same sorbent. The fully automated microextraction GC–MS protocol was evaluated for the influence of matrix substances typical for wastewater. Dilution of samples prior to MEPS is recommended when the polar caffeine is present at high concentration. Real water samples were analyzed by the MEPS-GC–MS method and compared to standard SPE.     

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%.     

Ultra trace analysis of 17 organochlorine pesticides in water samples from the Arctic based on the combination of solid-phase extraction and headspace solid-phase microextraction–gas chromatography-electron-capture detector

Solid-phase extraction (SPE) was combined with headspace solid-phase microextraction (HS-SPME) for the highly effective enrichment of 17 ultra trace organochlorine pesticides in water samples. The target compounds were successfully transferred from water samples to a gas chromatography capillary column by means of four consecutive steps, namely SPE, solvent conversion, HS-SPME, and thermal desorption of the SPME fiber. Parameters, including elution volume and breakthrough volume in the SPE step, temperature in the solvent conversion step, and fiber type, ionic strength, extraction temperature, extraction time, and pH in the SPME step were optimized to improve the performance of the method through either single factor comparative experiment or the orthogonal experimental design approach. After optimization, the method gave high sensitivity with a method detection limit ranging from 0.0018 to 0.027 ng L⁻¹, good repeatability with a relative standard deviation less than 20% (n = 4) and acceptable recovery with a value mostly exceeding 60%. External standard calibration was employed for the quantification, and a wide linear range (from 0.0010 to 60 ng mL⁻¹) with R² values ranging from 0.9988 to 0.9999 were observed. In the end, the method was successfully applied to the Arctic samples, and the results showed that, among all the organochlorine pesticides, hexachlorocyclohexanes (HCHs) were the most predominant in the Arctic surface water body with sum of their concentrations ranging from 0.262 to 3.156 ng L⁻¹.     

Preparation and characterization of metal-organic framework MIL-101(Cr)-coated solid-phase microextraction fiber

Metal-organic frameworks (MOFs) have received great attention as novel sorbents due to their fascinating structures and intriguing potential applications in various fields. In this work, a MIL-101(Cr)-coated solid-phase microextraction (SPME) fiber was fabricated by a simple direct coating method and applied to the determination of volatile compounds (BTEX, benzene, toluene, ethylbenzene, m-xylene and o-xylene) and semi-volatile compounds (PAHs, polycyclic aromatic hydrocarbons) from water samples. The extraction and desorption conditions of headspace SPME (HS-SPME) were optimized. Under the optimized conditions, the established methods exhibited excellent extraction performance. Good precision (<7.7%) and low detection limits (0.32–1.7 ng L⁻¹ and 0.12–2.1 ng L⁻¹ for BTEX and PAHs, respectively) were achieved. In addition, the MIL-101(Cr)-coated fiber possessed good thermal stability, and the fiber can be reused over 150 times. The fiber was successfully applied to the analysis of BTEX and PAHs in river water by coupling with gas chromatography–mass spectrometry (GC–MS). The analytes at low concentrations (1.7 and 10 ng L⁻¹) were detected, and the recoveries obtained with the spiked river water samples were in the range of 80.0–113% and 84.8–106% for BTEX and PAHs, respectively, which demonstrated the applicability of the self-made fiber.     

Simultaneous determination of multibenzodiazepines by HPLC/UV: Investigation of liquid-liquid and solid-phase extractions in human plasma

A method for simultaneous determination of seven benzodiazepines (BZPs) (flunitrazepam, clonazepam, oxazepam, lorazepam, chlordiazepoxide, nordiazepam and diazepam using N-desalkylflurazepam as internal standard) in human plasma using liquid-liquid and solid-phase extractions followed by high-performance liquid chromatography (HPLC) is described. The analytes were separated employing a LC-18 DB column (250 mm × 4.6 mm, 5 μm) at 35 °C under isocratic conditions using 5 mM KH₂PO₄ buffer solution pH 6.0:methanol:diethyl ether (55:40:5, v/v/v) as mobile phase at a flow rate of 0.8 mL min⁻¹. UV detection was carried out at 245 nm. Employing LLE, the best conditions were achieved with double extraction of 0.5 mL plasma using ethyl acetate and Na₂HPO₄ pH 9.5 for pH adjusting. Employing SPE, the best conditions were achieved with 0.5 mL plasma plus 3 mL 0.1 M borate buffer pH 9.5, which were then passed through a C18 cartridge previously conditioned, washed for 3 times with these solvents: 3 mL 0.1 M borate buffer pH 9.5, 4 mL Milli-Q water and 1 mL acetonitrile 5%, finally the BZPs elution was carried with diethyl ether:n-hexane:methanol (50:30:20). In both methods the solvent was evaporated at 40 °C under nitrogen flow. The validation parameters obtained in LLE were linearity range of 50-1200 ng mL⁻¹ plasma (r ≥ 0.9927), limits of quantification of 50 ng mL⁻¹ plasma, within-day and between-day CV% and E% for precision and accuracy lower than 15%, and recovery above 65% for all BZPs. In SPE, the parameter obtained were linearity range of 30-1200 ng mL⁻¹ plasma (r ≥ 0.9900), limits of quantification of 30 ng mL⁻¹ plasma, within-day and between-day CV% and E% for precision and accuracy lower than 15% and recovery above 55% for all BZPs. These extracting procedures followed by HPLC analysis showed their suitable applicability in order to examine one or more BZPs in human plasma. Moreover, it could be suggested that these procedures might be employed in various analytical applications, in special for toxicological/forensic analysis.     

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-performance liquid chromatography with fluorescence detection and ultra-performance liquid chromatography with electrospray tandem mass spectrometry method for the determination of indoleamine neurotransmitters and their metabolites in sea lamprey plasma

We present a comparison of two sensitive methods, HPLC with fluorescence detector (HPLC/FLD) and UPLC with electrospray tandem mass spectrometry (UPLC/MS/MS), for the determination of indoleamine neurotransmitters (NTs) and their metabolites in sea lamprey plasma samples. Liquid–liquid extraction (LLE) and solid-phase extraction (SPE) were also tested for recovery and matrix effect. The recoveries of SPE determined by HPLC/FLD and UPLC/MS/MS ranged from 75 to 123% and 78 to 105%, respectively, while the recoveries of LLE ranged from 45 to 73% and 48 to 75%, respectively. SPE combined with HPLC/FLD and UPLC/MS/MS to determine the target analytes in plasma samples were validated of the sensitivity, reproducibility, accuracy and precision. Both methods exhibited excellent linearity in the range of 0.2–50 ng mL⁻¹ for all analytes. The limits of detection (LOD) varied from 0.04 ng mL⁻¹ to 0.13 ng mL⁻¹ for HPLC/FLD method and 0.003 ng mL⁻¹ to 0.02 ng mL⁻¹ for UPLC/MS/MS method. The inter-day accuracy ranged from 82.5 to 127.0% for HPLC/FLD and 93.0 to 113.0% for UPLC/MS/MS. The inter-day precision ranged from 9.9 to 32.3% for HPLC/FLD and 5.4 to 13.2% for UPLC/MS/MS. These results demonstrated that the values obtained by both methods were within the satisfactory range and the UPLC/MS/MS method provided more accurate and precise measurements than HPLC/FLD method. The comparison is of great importance to determine the available detectors, considering the complexity and expensiveness versus quality parameters. These two methods were applied to the analysis of four important indoleamine neurotransmitter analytes (5-hydroxytryptamine, 5-hydroxyindole-3-acetic acid, tryptamine and melatonin) in sea lamprey plasma samples.     

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.     

Continuous-flow microextraction and gas chromatographic-mass spectrometric determination of polycyclic aromatic hydrocarbon compounds in water

A new method of the determination polycyclic aromatic hydrocarbons (PAHs) in water samples was developed by continuous-flow microextraction (CFME) coupled with gas chromatography-mass spectrometry (GC-MS). In this experiment, 15 mL sample solution with no salt-added was flowed at the rate of 1.0 mL min⁻¹ through 3 μL benzene as extraction solvent. Under the optimal extraction conditions, the developed method was found to yield a linear calibration curve in the concentration range from 0.05 to 15 ng mL⁻¹. Furthermore, the accuracy and repeatability of the method were good by calculating from water samples spiked at known concentrations of PAHs, and the recovery of optimal method was satisfactory. The results showed that CFME was an efficient preconcentration method for extraction of PAHs from spiked water samples.     

Enrichment of polycyclic aromatic hydrocarbons in seawater with magnesium oxide microspheres as a solid-phase extraction sorbent

The enrichment of polycyclic aromatic hydrocarbons (PAHs) in water samples with magnesium oxide (MgO) microspheres was evaluated, and four 3-5-ring PAHs were used as probes to validate the adsorption capacity of the material. Factors affecting the recovery of PAHs were investigated in detail, including the type and concentration of organic modifiers, elution solvents, particle size of the adsorbent, volume and flow rate of the samples, and the lifetime of MgO cartridges. The recoveries of four PAHs extracted from 20 mL of seawater spiked with standard PAHs ranged from 85.8% to 102.0% under the optimised conditions. The limits of detection varied from 1.83 ng L⁻¹ to 16.03 ng L⁻¹, indicating that the analytical method was highly sensitive. Additionally, the proposed method was successfully used to enrich PAHs in seawater. Compared to conventional methods, the proposed method consumed less organic modifier (5% acetone), and cheaper sorbents with comparable extraction efficiency were employed.     

Determination of simple bromophenols in marine fishes by reverse-phase high performance liquid chromatography (RP-HPLC)

Brominated phenols 2- and 4-bromophenol (2-BP and 4-BP); 2,4- and 2,6-dibromophenol (2,4-DBP and 2,6-DBP) and 2,4,6-tribromophenol (2,4,6-TBP) have been identified as key flavor compounds found in seafoods. Depending on their concentrations, they were responsible for marine or ocean flavor (shrimp/crab/fish/sea salt-like) or for phenolic/iodine/iodoform-like off-flavor. In this work a new analytical methodology was developed to determine, simultaneously, such bromophenols in fish meats, based on reversed-phased high-performance liquid chromatographic separation (RP-HPLC). The separation of bromophenols was made onto a Lichrospher 100 RP-18 column using water:acetonitrile gradient at a flow rate of 1.0 mL min⁻¹, using absorbance detection at 286 nm, were the 2-BP, 4-BP, 2,4- and 2,6-DBP show significant absorbtivity values and at 297 nm for 2,4,6-TBP. They were separated in 20 min with a good chromatographic resolution (Rs) for the isomeric compounds: 2- and 4-BP, Rs = 1.23; 2,4- and 2,6-DBP, Rs = 1.63. The calibration curves were linear in the bromophenols concentration range of 200.0-1000 ng mL⁻¹. Under optimized conditions, the detection limit of the HPLC method was 127 ng mL⁻¹ for 2-BP; 179 ng mL⁻¹ for 4-BP; 89.0 ng mL⁻¹ for 2,4-DBP; 269 ng mL⁻¹ for 2,6-DBP and 232 ng mL⁻¹ for 2,4,6-TBP. This method has been applied in determination of bromophenols, isolated by combined steam distillation-solvent extraction with 2 mL of pentane/diethyl ether (6:4), from Brazilian fishes samples, collected on the Atlantic coast of Bahia (13°01′S and 38°31′W), Brazil. The concentration range determined were 0.20 ng g⁻¹ (2-BP) to 299 ng g⁻¹ (2,4,6-TBP). The method proposed here is rapid and suitable for simultaneous quantification of simple bromophenols in fish meat. As long as we know, it is the first analytical methodology, using RP-HPLC/UV, which was developed to determine simple bromophenols in fish meat.     

The automation of the acquisition and evaluation of pyrolysis-gas chromatography-mass spectrometry data for paint samples

This study describes a sensitivity and selectivity approach based on gas chromatography-mass spectrometry to determinate morphine levels in rat biologic fluids. Optimized experimental conditions of solid-phase extraction (SPE), including pH of the sample, solvent composition, and various sorbents, are examined herein. The largest recovery is greater than 94.0% for morphine, is achieved with a mixed sorbent C₈/SCX and mixed elution CHCl₃/iso-propanol (9:1) at pH 6.8. Acetylation accomplished with acetic anhydride is utilized to derivatize morphine to 3,6-diacetylmorphine for GC/MS analysis. The proposed method was precise and a wide linear range from 0.5 to 500 ng mL⁻¹. A detection limit of 0.31 ng mL⁻¹ in urine is achieved. The maximum ratio of morphine glucuronide to morphine in the blood of rat is 6 to 1. A terminal half-life of morphine in blood is calculated as around 120 min.     

The investigation of electrospun polymer nanofibers as a solid-phase extraction sorbent for the determination of trazodone in human plasma

A novel micro-extraction procedure was developed through the use of an electrospun polymer nanofiber as a solid-phase extraction (SPE) sorbent to directly extract trazodone from human plasma. The target compound was then monitored by a high performance liquid chromatography with ultraviolet detector (HPLC-UV) system. Parameters of influencing the extraction efficiency, such as fiber diameter, fiber packing amount, eluted solvent, pH and ionic strength were investigated. Under the optimized conditions, a linear response for trazodone over the range of 20-2000 ng mL⁻¹ was achieved with a γ² value of 0.9996. The precision of the method was examined with relative standard deviations of 5.7, 2.7, 2.2% corresponding to 50, 200, and 500 ng mL⁻¹, respectively, of trazodone spiked into 0.1 mL of plasma samples. The extraction recoveries of 58.3-75.2% and the relative recoveries of 94.6-105.5% were obtained. The limit of detection (LOD) was determined to be 8 ng mL⁻¹. A 15 min of HPLC gradient was successfully applied to determine trazodone from human plasma. Due to its simplicity, selectivity and sensitivity, the method may be applied to pharmacokinetic and pharmacodynamic studies of drugs.     

Imprinted functionalized silica sol-gel for solid-phase extraction of triazolamin

A triazolam-imprinted silica microsphere was prepared by combining a surface molecular-imprinting technique with the sol-gel process. The results illustrate that the triazolam-imprinted silica microspheres provided using γ-aminopropyltriethoxysilane and phenyltrimethoxysilane as monomers exhibited higher selectivity than those provided from γ-aminopropyltriethoxysilane and methyltriethoxysilane. In addition, the optimum affinity occurred when the molar ratio of γ-aminopropyltriethoxysilane, phenyltrimethoxysilane, and the template molecule was 4.2:4.7:0.6. Retention factor (k) and imprinting factor (IF) of triazolam on the imprinted and non-imprinted silica microsphere columns were characterized using high performance liquid chromatography (HPLC) with different mobile phases including methanol, acetonitrile, and water solutions. The molecular selectivity of the imprinted silica microspheres was also evaluated for triazolam and its analogue compounds in various mobile phases. The better results indicated that k and IF of triazolam on the imprinted silica microsphere column were 2.1 and 35, respectively, when using methanol/water (1/1, v/v) as the mobile phase. Finally, the imprinted silica was applied as a sorbent in solid-phase extraction (SPE), to selectively extract triazolam and its metabolite, α-hydroxytriazolam, from human urine samples. The limits of detection (LOD) for triazolam and α-hydroxytriazolam in urine samples were 30 ± 0.21 ng mL⁻¹ and 33 ± 0.26 ng mL⁻¹, respectively.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between tetracarboxy aluminum phthalocyanine and tetra-N-hexadecylpyridiniumyl porphyrin

A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC₄Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC₁₆PyP). The fluorescence of the AlC₄Pc, with the maximum emission wavelength at 701 nm, could be quenched by TC₁₆PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200 ng mL⁻¹ for fish sperm DNA (FS DNA) and 2-400 ng mL⁻¹ for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59 ng mL⁻¹ for FS DNA and 0.82 ng mL⁻¹ for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

Adsorptive stripping square wave voltammetry (Ad-SSWV) accomplished with second-order multivariate calibration determination of fenitrothion and its metabolites in river water samples

A method, using stripping square wave voltammetry (Ad-SSWV), for the simultaneous determination of fenitrothion (FEN) and its metabolites: fenitrooxon (OXON) and 3-methyl-4-nitrophenol (3-MET) in environmental samples is reported. All three compounds produce, at mercury electrode (HMDE), an electrochemical signal due to an adsorptive-reductive process. The electrochemical approach shows a very high overlap degree for FEN and OXON voltammograms, however the adsorption kinetic profile could be used as an additional differential variable between both analytes. Second-order multivariate calibration has been tested to solve the mixture of the three compounds. The second-order assayed methods were parallel factor analysis (PARAFAC), unfolded partial least squares (U-PLS), multidimensional partial least squares (N-PLS) and the latest ones were used in combination with the residual bilinearization procedure RBL. U-PLS/RBL model was stated as the best second-order algorithm for the simultaneous determination of these three compounds up to 50 ng mL⁻¹ for each analyte. The detection limits and recovery values were 1.6 ng mL⁻¹ and 92 ± 7% for FEN; 3.7 ng mL⁻¹ and 101 ± 9% for OXON and 0.6 ng mL⁻¹ and 97 ± 8% for 3-MET.     

Leachability and analytical speciation of antimony in coal fly ash

A new procedure was described with multiwalled carbon nanotubes as solid phase extraction packing material for the trace analysis of nicosulfuron, thifensulfuron and metsulfuron-methyl in water samples. The possible parameters influencing the enrichment were optimized and the optimal conditions were as followed: eluent, sample pH, flow rate and sample volume were acetonitrile containing 1% acetic acid, pH 3, 8 mL min⁻¹ and 500 mL, respectively. Under the optimal chromatographic separation and SPE conditions, the linear range, detection limit (S/N = 3) and precision (R.S.D., n = 6) were 0.04-40 ng mL⁻¹, 6.8 ng L⁻¹ and 2.5% for nicosulfuron, 0.04-40 ng mL⁻¹, 11.2 ng L⁻¹ and 5.4% for thifensulfuron, 0.02-20 ng mL⁻¹, 5.9 ng L⁻¹, 2.1% for metsulfuron-methyl, respectively. The established method was well employed to determine nicosulfuron, thifensulfuron and metsulfuron-methyl in tap water, seawater, reservoir water and well water samples, and satisfactory results were obtained, the spiked recoveries in the range of 87.2-100.7%, 96.5-105.6% and 83.7-111.1% for them each, respectively.