Application of a validated stability-indicating densitometric thin-layer chromatographic method to stress degradation studies on moxifloxacin

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-ethanol-6 M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298 nm. Compact spots for moxifloxacin were found at R_f value of 0.58 ± 0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9925 in the working concentration range of 100-800 ng spot⁻¹. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83 ng spot⁻¹, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different R_f values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2-10.8 was studied.     

Validated stability-indicating densitometric thin-layer chromatography: application to stress degradation studies of minocycline

A simple, stability-indicating high-performance thin-layer liquid chromatographic (HPTLC) method for analysis of minocycline was developed and validated. The densitometric analysis was carried out at 345 nm using methanol-acetonitrile-isopropyl alcohol-water (5:4:0.5:0.5, v/v/v/v) as mobile phase.The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. To achieve good result, plates were sprayed with a 10% (w/v) solution of disodium ethylene diaminetetraacetic acid (EDTA), the pH of which was adjusted to 9.0. Compact spots of minocycline were found at R_f = 0.30 ± 0.02. For proposed procedure, linearity (r = 0.9997), limit of detection (3.7 ng spot⁻¹), recovery (99.23-100.16%), and precision (% R.S.D. ≤ 0.364) was found to be satisfactory. The drug undergoes acidic and basic degradation, oxidation and photodegradation. All the peaks of degradation products were well resolved from the pure drug with significantly different R_f values. The acidic and alkaline degradation kinetics of minocycline, evaluated using this method, is found to be of first order.     

Determination of human IgG by solid substrate room temperature phosphorescence immunoassay based on an antibody labeled with nanoparticles containing dibromofluorescein luminescent molecules

Luminescent silicon dioxide nano-particles with size of 20 nm, which containing dibromofluorescein (D) were synthesized by sol-gel method (symbolized by D-SiO₂).The particles can emit intense and stable room temperature phosphorescence signal on polyamide membrane when Pb(Ac)₂ was used as a heavy atom perturber. The λ_exmax/λ_emmax was 457/622 nm. Our research indicated that the specific immune reaction between goat-anti-human IgG antibody labeled with D-SiO₂ and human IgG could be carried out on polyamide membrane quantitatively, and the phosphorescence intensity of the particle was enhanced after the immunoreactions. Thus a new method of solid substrate room temperature phosphorescence immunoassay (SS-RTP-IA) for the determination of human IgG was established basing on antibody labeled with the D-SiO₂ nanoparticles. The linear range of this method was 0.0624-20.0 pg human IgG spot⁻¹ (corresponding concentration: 0.156-50.0 ng ml⁻¹, the sample volume: 0.40 μl spot⁻¹) with a limit of detection (LD) as 0.018 pg spot⁻¹, and the regression equation of working curve was ΔI_p = 7.201 m_IgG (pg spot⁻¹) + 82.57. Samples containing 0.156 and 50.0 ng ml⁻¹ of IgG were measured repeatedly for 11 times and R.S.D.s were 4.1 and 3.4%, respectively. Results showed that this method had the merits as sensitive, accurate and precise.     

Validated high-performance thin-layer chromatography method for determination of trigonelline in herbal extract and pharmaceutical dosage form

A new, simple, sensitive, selective, precise and robust high-performance thin-layer chromatographic (HPTLC) method for analysis of trigonelline was developed and validated for the determination of trigonelline in herbal extracts and in pharmaceutical dosage forms. Analysis of trigonelline was performed on TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. Linear ascending development was carried out in twin trough glass chamber saturated with mobile phase consisting of n-propanol-methanol-water (4:1:4, v/v/v) at room temperature (25 ± 2 °C). Camag TLC scanner III was used for spectrodensitometric scanning and analysis in absorbance mode at 269 nm. The system was found to give compact spots for trigonelline (R_f value of 0.46 ± 0.02). The linear regression analysis data for the calibration plots showed good linear relationship with r² = 0.9991 ± 0.0002 in the concentration range 100-1200 ng spot⁻¹ with respect to peak area. According to the International Conference on Harmonization (ICH) guidelines the method was validated for precision, recovery, robustness and ruggedness. The limits of detection and quantification were determined. The trigonelline content of herbal extracts quantified and estimated from the formulation was found to be well within limits (±5% of the labeled content of the formulations). Statistical analysis of the data showed that the method is reproducible and selective for the estimation of trigonelline.     

Determination of tadalafil in pharmaceutical preparation by HPLC using monolithic silica column

The simple, reliable and reproducible HPLC and extraction methods were developed for the analysis of tadalafil in pharmaceutical preparation. The column used was monolithic silica column, Chromolith Performance RP-18e (100 mm × 4.6 mm, i.d.). The mobile phase used was phosphate buffer (100 mM, pH 3.0)-acetonitrile (80:20, v/v) at the flow rate of 5 mL min⁻¹ with UV detection at 230 nm at ambient temperature. Extraction of tadalafil from tablet was carried out using methanol. Linearity was observed in the concentration range from 100 to 5000 ng mL⁻¹ for tadalafil with a correlation coefficient (R²) 0.9999 and 100 ng mL⁻¹ as the limit of detection. The values of linearity range, correlation coefficient (R²) and limit of detection were 50-5000 ng mL⁻¹, 0.9999-50 ng mL⁻¹, respectively for sildenafil. Parameters of validation prove the precision of the method and its applicability for the determination of tadalafil in pharmaceutical tablet formulation. The method is suitable for high throughput analysis of the drug.     

Rapid and accurate determination of thallium in seawater using SF-ICP-MS

We present a method for the rapid and direct determination of dissolved Thallium (Tl) using high resolution sector field inductively coupled mass spectrometry (SF-ICP-MS) suitable for the measurement of large time series (e.g. during monitoring). Thallium data are presented for a series of natural sea water samples, which were validated with sea water standards CASS-4 and NASS-5. The sea water samples and standards were diluted 10 times prior to measurement with SF-ICP-MS in low resolution mode (R = 300, LR). For both CASS-4 and NASS-5 (salinity of 30.5) we calculated a concentration of about 11 ng L⁻¹ when using Tl values of 14 ± 2 ng L⁻¹ (at salinity of 35 ± 1) published by Flegal and Patterson [1] for Atlantic and Pacific sea water. For CASS-4 we report a Tl value of 10.6 ± 0.7 ng L⁻¹ (n = 70), for NASS-5 a Tl value of 10.3 ± 0.8 ng L⁻¹ (n = 11). For Tl in both CASS-4 and NASS-5, the overall error in accuracy and precision is less than 4% and 8% (2 s), respectively. Further, values of 7.7 ± 0.3 and 6.7 ± 0.2 ng L⁻¹ Tl were found for the estuarine standard SLEW-3 (salinity of 15) and the river water standard SLRS-4, respectively, for which no certified value exists so far. The detection and quantification limits of our method are 0.1 and 0.3 ng L⁻¹, respectively. Slight differences in the accuracy of our method and other published methods for the determination of Tl in sea water are discussed. Time-series of natural coastal water samples gave Tl values (6-12 ng L⁻¹), which correspond to determined salinities, and hence, appear realistic and oceanographically consistent.     

Dispersive liquid-liquid microextraction versus single-drop microextraction for the determination of several endocrine-disrupting phenols from seawaters

Two liquid-phase microextraction procedures: single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), have been developed for the determination of several endocrine-disrupting phenols (EDPs) in seawaters, in combination with high-performance liquid chromatography (HPLC) with UV detection. The EDPs studied were bisphenol-A, 4-cumylphenol, 4-tertbutylphenol, 4-octylphenol and 4-n-nonylphenol. The optimized SDME method used 2.5 μL of decanol suspended at the tip of a micro-syringe immersed in 5 mL of seawater sample, and 60 min for the extraction time. The performance of the SDME is characterized for average relative recoveries of 102 ± 11%, precision values (RSD) < 9.4% (spiked level of 50 ng mL⁻¹), and detection limits between 4 and 9 ng mL⁻¹. The optimized DLLME method used 150 μL of a mixture acetonitrile:decanol (ratio 15.7, v/v), which is quickly added to 5 mL of seawater sample, then subjected to vortex during 4 min and centrifuged at 2000 rpm for another 5 min. The performance of the DLLME is characterized for average relative recoveries of 98.7 ± 3.7%, precision values (RSD) < 7.2% (spiked level of 20 ng mL⁻¹), and detection limits between 0.2 and 1.6 ng mL⁻¹. The efficiencies of both methods have also been compared with spiked real seawater samples. The DLLME method has shown to be a more efficient approach for the determination of EDPs in seawater matrices, presenting enrichment factors ranging from 123 to 275, average relative recoveries of 110 ± 11%, and precision values (RSD) < 14%, when using a real seawaters (spiked level of 3.5 ng mL⁻¹).     

Flow-through optosensing of 1-naphthaleneacetic acid in water and apples by heavy atom induced-room temperature phosphorescence measurements

A sensitive and selective phosphorimetric method for the determination of 1-naphthaleneacetic acid (1-NAA) based on a flow-injection system connected to a flow cell packed with a solid support and placed in the sample compartment of a conventional luminescence spectrometer is described. A non-ionic solid polymeric resin Amberlite XAD-7 is used for the packing. After injection of the sample, 1-NAA is on-line retained in the packed resin and measurements of the heavy atom induced (HAI)-room temperature phosphorescence (RTP) emission (λ_ex/λ_em = 292/490 nm) from this native luminescent compound are taken.The optimum experimental conditions were investigated by injecting 2 ml samples of an aqueous solution of 1-NAA in the flow system. A concentration 0.15 mol l⁻¹ of thallium(I) ions, as heavy atom, both in the samples and the carrier flow, was finally selected. Also, a concentration of 6 mmol l⁻¹ of sulphite was optimal for ensuring the necessary deoxygenation of the system at the selected flow rate of 0.8 ml min⁻¹. After measurement, the solid support was efficiently regenerated by injecting 1 ml of a mixture water:acetone in a ratio 1:1 (v/v) into the flow.The detection limit (3σ criterion) was 1.2 ng ml⁻¹ of 1-NAA. The repeatability (R.S.D.) for five replicates of a sample containing 50 ng ml⁻¹ of analyte turned out to be ±3% and the calibration graphs proved to be linear up to 500 ng ml⁻¹ of 1-NAA (maximum concentration assayed). The effect of potential interferences from other organic species which can be also used as plant growth regulators, as well as from various inorganic cations and anions, has been investigated as well.The method was successfully applied to the determination of low levels of this plant growth regulator in natural waters (river and fountain waters) and apples.     

Cold vapour atomic fluorescence determination of mercury in milk by slurry sampling using multicommutation

A highly sensitive mechanized method has been developed for the determination of mercury in milk by atomic fluorescence spectrometry (AFS). Samples were sonicated for 10 min in an ultrasound water bath in the presence of 8% (v/v) aqua regia, 2% (v/v) antifoam A and 1% (m/v) hydroxilamine hydrochloride, and after that, they were treated with 8 mmol l⁻¹ KBr and 1.6 mmol l⁻¹ KBrO₃ in an hydrochloric medium. Atomic fluorescence measurements were made by multicommutation, which provides a fast alternative in quality control analysis, due to the easy treatment of a large number of samples (approximately 70 h⁻¹), and is an environmentally friendly procedure, which involves a waste generation of only 94.5 ml h⁻¹ as compared with the 605 ml h⁻¹ obtained by using continuous AFS measurements. The limit of detection found was 0.011 ng g⁻¹ Hg in the original sample. The method provided a relative standard deviation of 3.4% for five independent analysis of a sample containing 0.30 ng g⁻¹ Hg. To validate the accuracy of the method, a certified reference material NIST-1459 (non-fat milk powder) containing 0.3±0.2 ng g⁻¹ Hg was analysed and a value of 0.27±0.06 ng g⁻¹ Hg was found. A comparison made between data found by the developed procedure and those obtained by microwave-assisted digestion and continuous AFS measurements evidenced a good comparability between these two strategies. Results obtained for commercially available milk samples varied between 0.09 and 0.61 ng g⁻¹ Hg depending on the type of sample and its origin. The confluence of the analytical waste with a 6 mol l⁻¹ NaOH allowed us to reduce the waste generation in a working session from 1 l to 5 g solid residue with a matrix of Fe(OH)₃ which contributes to the deactivation of traces of heavy metals presents in the samples that does not form volatile hydrides.     

Method development and optimization for the determination of selenium in bean and soil samples using hydride generation electrothermal atomic absorption spectrometry

The present investigation is the first part of an initiative to prepare a regional map of the natural abundance of selenium in various areas of Brazil, based on the analysis of bean and soil samples. Continuous-flow hydride generation electrothermal atomic absorption spectrometry (HG-ET AAS) with in situ trapping on an iridium-coated graphite tube has been chosen because of the high sensitivity and relative simplicity. The microwave-assisted acid digestion for bean and soil samples was tested for complete recovery of inorganic and organic selenium compounds (selenomethionine). The reduction of Se(VI) to Se(IV) was optimized in order to guarantee that there is no back-oxidation, which is of importance when digested samples are not analyzed immediately after the reduction step. The limits of detection and quantification of the method were 30 ng L⁻¹ Se and 101 ng L⁻¹ Se, respectively, corresponding to about 3 ng g⁻¹ and 10 ng g⁻¹, respectively, in the solid samples, considering a typical dilution factor of 100 for the digestion process. The results obtained for two certified food reference materials (CRM), soybean and rice, and for a soil and sediment CRM confirmed the validity of the investigated method. The selenium content found in a number of selected bean samples varied between 5.5 ± 0.4 ng g⁻¹ and 1726 ± 55 ng g⁻¹, and that in soil samples varied between 113 ± 6.5 ng g⁻¹ and 1692 ± 21 ng g⁻¹.     

Rapid determination of trans-resveratrol in red wine by solid-phase microextraction with on-fiber derivatization and multidimensional gas chromatography–mass spectrometry

There has been considerable public interest and a growing number of scientific studies linking certain phenolic compounds in grapes and wines, particularly trans-resveratrol (trans-3,5,4′-trihydroxystilbene, TRA), to human health benefits. Typical TRA concentrations in wine are very low. It is a polar compound with very low volatility, which makes it difficult to extract and to separate on a gas chromatography (GC) column without derivatization. In this study, a new method for trace analysis of TRA was developed using solid-phase microextraction (SPME) with on-fiber silylation derivatization. Multidimensional GC equipped with a heartcut valve and cryogenic focusing was coupled with a mass-selective detector and used for improved separations and analysis. The effects of SPME fiber selection, extraction time, temperature, and desorption time were investigated. The derivatization conditions, time/temperature and the volume of derivatization reagent were also optimized. The calibration curve was linear over the concentration range from 10 ng L⁻¹ to 5 mg L⁻¹, with a correlation coefficient of 0.9996. The average recovery of TRA in red wine was 83.6 ± 5.6%. The method detection limit (MDL) for TRA in ethanol:water (12.5:87.5, v/v) solution in this study was 7.08 ng L⁻¹ whereas the MDL for TRA in pure water was 2.85 ng L⁻¹. The new method was used to test the TRA content in six selected Iowa red wine samples. Measured concentrations varied from 12.72 to 851.9 μg L⁻¹.     

Simultaneous determination of sulfamonomethoxine, sulfadimethoxine, and their hydroxy/N(4)-acetyl metabolites with gradient liquid chromatography in chicken plasma, tissues, and eggs

A simultaneous determination of sulfamonomethoxine, sulfadimethoxine, and their hydroxy/N⁴-acetyl metabolites in chicken plasma, muscle, liver, and eggs using gradient high-performance liquid chromatography (HPLC) with a photo-diode array detector is developed. All the compounds are extracted by a handheld ultrasonic homogenizer with ethanol followed by centrifugation. The separation is performed by a reversed-phase C4 column with a gradient elution (ethanol:1% (v/v) acetic acid, v/v; 10:90 → 20:80). Average recoveries from samples spiked at 0.1-1.0 μg g⁻¹ or μg ml⁻¹ for each drug were >90% with relative standard deviations within 4%. The limits of quantitation were <30 ng g⁻¹ or ng ml⁻¹.     

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10 min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH₄ in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1 ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7 ng l⁻¹ for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2 ng g⁻¹ As, from 3.1±0.2 to 11.6±0.4 ng g⁻¹ Sb, from 10.7±0.5 to 25.5±0.4 ng g⁻¹ Se, from 0.9±0.2 to 9.4±0.6 ng g⁻¹ Te and from 11.5±0.1 to 27.7±0.4 ng g⁻¹ Bi.     

Determination of mercury species with a resin functionalized with a 1,2-bis(o-aminophenylthio)ethane moiety

A method for the simultaneous preconcentration and determination of Hg(II) and MeHg(I) at the ng ml⁻¹ level has been developed. This method is based on solid phase extraction using a newly synthesized chelating resin containing nitrogen and sulphur donor sites of the 1,2-bis(o-aminophenylthio)ethane moiety that is very selective for mercury. The characterization of the resin has been carried out by elemental analyses, infrared spectral data, thermogravimetric analysis and metal ion capacities. The resin is highly selective for Hg(II) and MeHg(I) with an exchange capacity of 0.38 and 0.30 mmol g⁻¹, respectively. Various parameters like pH, column flow rate, desorbing agents are optimized. Cold vapour atomic absorption spectrometry (CVAAS) was used to measure the concentration of both species of mercury. The calibration graph was linear upto 10 ng ml⁻¹ with a 3σ detection limit of 0.09 ng ml⁻¹. The recovery of Hg(II) and MeHg(I) was found to be 98.9±2.0 and 98.0±1.1%, respectively. The method has been used for routine determination of trace levels of mercury species in natural waters to comply with more stringent regulations.     

Enantioselective analysis of mirtazapine and its two major metabolites in human plasma by liquid chromatography-mass spectrometry after three-phase liquid-phase microextraction

A three-phase liquid-phase microextraction (LPME) method using porous polypropylene hollow fibre membrane with a sealed end was developed for the extraction of mirtazapine (MRT) and its two major metabolites, 8-hydroxymirtazapine (8-OHM) and demethylmirtazapine (DMR), from human plasma. The analytes were extracted from 1.0 mL of plasma, previously diluted and alkalinized with 3.0 mL 0.5 mol L⁻¹ pH 8 phosphate buffer solution and supplemented with 15% sodium chloride (NaCl), using n-hexyl ether as organic solvent and 0.01 moL L⁻¹ acetic acid solution as the acceptor phase. Haloperidol was used as internal standard. The chromatographic analyses were carried out on a chiral column, using acetonitrile-methanol-ethanol (98:1:1, v/v/v) plus 0.2% diethylamine as mobile phase, at a flow rate of 1.0 mL min⁻¹. Multi-reaction monitoring (MRM) detection was performed by mass spectrometry (MS-MS) using a triple-stage quadrupole and electrospray ionization interface operating in the positive ion mode. The mean recoveries were in 18.3-45.5% range with linear responses over the 1.25-125 ng mL⁻¹ concentration range for all enantiomers evaluated. The quantification limit (LOQ) was 1.25 ng mL⁻¹. Within-day and between-day assay precision and accuracy (2.5, 50 and 100 ng mL⁻¹) showed relative standard deviation and the relative error lower than 11.9% for all enantiomers evaluated. Finally, the method was successfully used for the determination of mirtazapine and its metabolite enantiomers in plasma samples obtained after single drug administration of mirtazapine to a healthy volunteer.     

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.     

A novel flow-through fluorescence optosensor for the determination of thiabendazole

This paper presents the development of a new flow-injection system combined with solid-surface fluorescence detection for the determination of the widely used fungicide thiabendazole. Nylon powder was probed as a novel solid support for building the optosensor. The method is based on the on-line immobilization of thiabendazole onto nylon in a continuous flow system, followed by the measurement of its native fluorescence. Aqueous samples are directly injected in a water carrier, resulting in a very simple and economical method. The analytical figures of merit obtained using 1500 μL of sample and 75% methanol (v/v) as eluting solution were: linear calibration range from 8 to 120 ng mL⁻¹ (the lowest value corresponds to the quantitation limit), relative standard deviation, 0.9% (n = 5) at a level of 64 ng mL⁻¹, limit of detection calculated according to 1995 IUPAC recommendations is to 2.8 ng mL⁻¹, and sampling rate of 14 samples h⁻¹. The potential interference from other agrochemicals, metal ions and common anions, and the viability of determining thiabendazole in real water samples were also evaluated.     

A comparison of solid-phase microextraction and stir bar sorptive extraction coupled to liquid chromatography for the rapid analysis of resveratrol isomers in wines, musts and fruit juices

A comparison of direct immersion solid-phase microextraction (DI-SPME) and stir bar sorptive extraction (SBSE) coupled to liquid chromatography (HPLC) with fluorimetric detection for the rapid analysis of resveratrol isomers is described. For DI-SPME, a polar Carbowax-template resin (CW/TPR) 50 μm fiber was the most efficient and optimum extraction conditions were 40 °C and an extraction time of 30 min, stirring in the presence of 5% (m/v) sodium chloride and 0.07 M acetate/acetic acid buffer (pH 6). Desorption was carried out using the static mode for 10 min. Linearity was obtained in the 5-150 and 2-150 ng mL⁻¹ ranges for trans- and cis-resveratrol, with detection limits of 2 and 0.5 ng mL⁻¹, respectively. When using SBSE, a polydimethylsiloxane (PDMS) twister provided best extraction by means of a derivatization reaction in the presence of acetic anhydride and potassium carbonate. The same time and temperature were used for the extraction step in the presence of 2.5% (m/v) sodium chloride, and liquid desorption was performed with 150 μL of a 50/50 (v/v) acetonitrile/1% (v/v) acetic acid solution in a desorption time of 15 min. Linearity was now between 0.5 and 50 ng mL⁻¹ for trans-resveratrol with a detection limit of 0.1 ng mL⁻¹, while cis-resveratrol could not be extracted. The proposed methods were successfully applied to determining the resveratrol isomer content of wine, must and fruit juices.     

Novel polyamide-based nanofibers prepared by electrospinning technique for headspace solid-phase microextraction of phenol and chlorophenols from environmental samples

A novel solid phase microextraction (SPME) fiber was fabricated by electrospinning method in which a polymeric solution was converted to nanofibers using high voltages. A thin stainless steel wire was coated by the network of polymeric nanofibers. The polymeric nanofiber coating on the wire was mechanically stable due to the fine and continuous nanofibers formation around the wire with a three dimensional structure. Polyamide (nylon 6), due to its suitable characteristics was used to prepare the unbreakable SPME nanofiber. The scanning electron microscopy (SEM) images of this new coating showed a diameter range of 100–200 nm for polyamide nanofibers with a homogeneous and porous surface structure. The extraction efficiency of new coating was investigated for headspace solid-phase microextraction (HS-SPME) of some environmentally important chlorophenols from aqueous samples followed by gas chromatography–mass spectrometry (GC–MS) analysis. Effect of different parameters influencing the extraction efficiency including extraction temperature, extraction time, ionic strength and polyamide amount were investigated and optimized. In order to improve the chromatographic behavior of phenolic compounds, all the analytes were derivatized prior to the extraction process using basic acetic anhydride. The detection limits of the method under optimized conditions were in the range of 2–10 ng L⁻¹. The relative standard deviations (RSD) (n = 3) at the concentration level of 1.7–6.7 ng mL⁻¹ were obtained between 1 and 7.4%. The calibration curves of chlorophenols showed linearity in the range of 27–1330 ng L⁻¹ for phenol and monochlorophenols and 7–1000 ng L⁻¹ for dichloro and trichlorophenols. Also, the proposed method was successfully applied to the extraction of phenol and chlorophenols from real water samples and relative recoveries were between 84 and 98% for all the selected analytes except for 2,4,6 tricholophenol which was between 72 and 74%.     

Simultaneous determination of psychotropic drugs in human urine by capillary electrophoresis with electrochemiluminescence detection

Amitriptyline, doxepin and chlorpromazine are often used as psychotropic drugs in treatment of the various mental diseases, and are also partly excreted by kidney. This work developed a simple, selective and sensitive method for their simultaneous monitoring in human urine using capillary electrophoresis coupled with electrochemiluminescence (ECL) detection based on end-column ECL reaction of tris-(2,2′-bipyridyl)ruthenium(II) with aliphatic tertiary amino moieties. Acetone was used as an additive to the running buffer to obtain their absolute separation. Under optimized conditions the proposed method displayed a linear range from 5.0 to 800 ng mL⁻¹ for the three drugs with the correlation coefficients more than 0.995 (n = 8). Their limits of detection were 0.8 ng mL⁻¹ (3.6 fg), 1.0 ng mL⁻¹ (4.5 fg) and 1.5 ng mL⁻¹ (6.8 fg) at a signal to noise ratio of 3, respectively. The relative standard deviations for five determinations of 20 ng mL⁻¹ amitriptyline, doxepin and chlorpromazine were 1.7%, 4.2% and 3.6%, respectively. For practical application an extract step with 90:10 heptane/ethyl acetate (v/v) was performed to eliminate the influence of ionic strength in sample. The recoveries of amitriptyline, doxepin and chlorpromazine at different levels in human urine were between 83% and 93%, which showed that the method was valuable in clinical and biochemical laboratories for monitoring amitriptyline, doxepin and chlorpromazine.