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A fast and very selective flow-through phosphorescence optosensor was designed and characterized for the determination of the fungicide thiabendazole in water samples. For the first time, thiabendazole was determined using a flow-through optosensor based on the phosphorescence signals obtained when it is retained in a solid support. While thiabendazole does not phosphoresce in packing materials commonly used to fill the flow-cell, significant emission signals are observed when it is retained on nylon powder in the presence of iodide and sulfite. The experimental set-up was based on a flow-injection manifold coupled to an on-line phosphorescence detector containing nylon powder packed in a conventional flow-cell. Potassium iodide and sodium sulfite were added to sample aliquots to improve the thiabendazole phosphorescence and injected in the flow manifold using water as carrier. After the phosphorescence emission was registered, the analyte was eluted from the packed nylon with a 65% (v/v) methanol-water mixture. Optimal instrumentation, experimental and flow conditions were evaluated. Using a sample volume of 2000 microL, the analytical signal showed a very good linearity in the range 12.9-110 ng mL(-1), with a detection limit of 4.5 ng mL(-1), and a sample throughput of about 14 samples per hour. The effects of the presence of concomitant species in the thiabendazole phosphorescence signal were studied, and a comparison with the fluorescence nylon-powder optosensor was carried out and discussed. Finally, the applicability of the proposed optosensor was tested in water samples, and satisfactory recoveries ranging between 97% and 105% were obtained.

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Different second-order multivariate calibration algorithms, namely parallel factor analysis (PARAFAC), N-dimensional partial least-squares (N-PLS) and multivariate curve resolution-alternating least-squares (MCR-ALS) have been compared for the analysis of four fluoroquinolones in aqueous solutions, including some human urine samples (additional four fluoroquinolones were simultaneously determined by univariate calibration). Data were measured in a short time with a chromatographic system operating in the isocratic mode. The detection system consisted of a fast-scanning spectrofluorimeter, which allows one to obtain second-order data matrices containing the fluorescence intensity as a function of retention time and emission wavelength. The developed approach enabled us to determine eight analytes, some of them with overlapped profiles, without the necessity of applying an elution gradient, and thus significantly reducing both the experimental time and complexity. The study was employed for the discussion of the scopes of the applied second-order chemometric tools. The quality of the proposed technique coupled to each of the evaluated algorithms was assessed on the basis of the figures of merit for the determination of fluoroquinolones in the analyzed water and urine samples. Univariate calibration of four analytes led to limits of detection in the range 20-40 ng mL(-1) and root mean square errors for the validation samples in the range 30-60 ng mL(-1) (corresponding to relative prediction errors of 3-8%). The ranges for second-order multivariate calibration (using PARAFAC and N-PLS) of the remaining four analytes were: limit of detection, 2-8 ng mL(-1), root mean square errors, 3-50 ng mL(-1) and relative prediction errors, 1-5%.

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Very simple and highly sensitive methods are presented for the determination of benzo[a]pyrene, one of the most carcinogenic polycyclic aromatic hydrocarbons (PAHs). The approaches are based on solid-phase extraction of the analyte on a nylon membrane via a syringe procedure, and its fluorescent or phosphorescent determination on the solid surface. While the native fluorescence of benzo[a]pyrene retained on a nylon surface is measured directly, room-temperature phosphorescence is induced by spotting a few microlitres of thallium(I) nitrate solution on the surface (heavy-atom effect). An enhancement of the phosphorescence signal was corroborated when the measurements were carried under a nitrogen atmosphere. The analytical figures of merit obtained under the best experimental conditions demonstrate the capability of detecting benzo[a]pyrene at a sub-parts-per-trillion (sub-ng L(-1)) level. The potential interference from other common PAHs and also from different metal ions was studied. The feasibility of determining benzo[a]pyrene in real samples was successfully evaluated through the analysis of spiked tap, underground and mineral water samples of different origins. Recoveries obtained from spiked river waters were successfully compared with those provided by a reference method, through rigorous statistical analysis.

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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 microL 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.

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A spectrofluorimetric method has been developed for the quantitative determination of mefenamic, flufenamic, and meclofenamic acids in urine samples. The method is based on second-order data multivariate calibration (unfolded partial least squares (unfolded-PLS), multi-way PLS (N-PLS), parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD), and bilinear least squares (BLLS)). The analytes were extracted from the urine samples in chloroform prior to the determination. The chloroform extraction was optimized for each analyte, studying the agitation time and the extraction pH, and the optimum values were 10 minutes and pH 3.5, respectively. The concentration ranges in chloroform solution of each of the analytes, used to construct the calibration matrix, were selected in the ranges from 0.15 to 0.8 microg mL-1 for flufenamic and meclofenamic acids and from 0.25 to 3.0 microg mL-1 for mefenamic acid. The combination of chloroform extraction and second-order calibration methods, using the excitation-emission matrices (EEMs) of the three analytes as analytical signals, allowed their simultaneous determination in human urine samples, in the range of approximately 80 mg L-1 to 250 mg L-1, with satisfactory results for all the assayed methods. Improved results over unfolded-PLS and N-PLS were found with PARAFAC, SWATLD, and BLLS, methods that exploit the second-order advantage.

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This paper discusses the first analytical determination of the widely used fungicide thiabendazole by nylon-induced phosphorimetry. Nylon was investigated as a novel solid-matrix for inducing room-temperature phosphorescence of thiabendazole, which was enhanced under the effect of external heavy-atom salts. Among the investigated salts, lead(II) acetate was the most effective in yielding a high phosphorescence signal. An additional enhancement of the phosphorescence emission was attained when the measurements were carried out under a nitrogen atmosphere. There was only a moderate increase in the presence of cyclodextrins. The room-temperature phosphorescence lifetimes of the adsorbed thiabendazole were measured under different working conditions and, in all cases, two decaying components were detected. On the basis of the obtained results, a very simple and sensitive phosphorimetric method for the determination of thiabendazole was established. The analytical figures of merit obtained under the best experimental conditions were: linear calibration range from 0.031 to 0.26 microg ml(-1) (the lowest value corresponds to the quantitation limit), relative standard deviation, 2.4% (n=5) at a level of 0.096 microg ml(-1), and limit of detection calculated according to 1995 IUPAC Recommendations equal to 0.010 microg ml(-1) (0.03 ng/spot). The potential interference from common agrochemicals was also studied. The feasibility of determining thiabendazole in real samples was successfully evaluated through the analysis of spiked river, tap and mineral water samples.

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A rapid and sensitive method for the determination of naproxen and salicylate in serum is presented. The employed strategy combines solid-phase extraction on a reverse-phase membrane with spectrofluorimetry. Solid-phase extraction under optimum pH conditions makes NX to be retained over the solid surface (where it is directly determined by a fluorimetric technique). Salicylate passes through the disk and is also fluorimetrically determined, but in solution. The linear calibration ranges for NX in the membrane and salicylate in solution were 0.014-0.250 and 0.010-0.250 microg ml(-1), respectively. The lowest value, in each case, is the corresponding limit of quantitation. The performance of the method is demonstrated with the successful determination of both drugs in spiked and real human serum samples.

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The inclusion complexation of ibuprofen in beta-cyclodextrin (beta-CD) has been examined by means of spectrofluorimetry at both acid and alkaline pH. The results suggest that stable 1:1 complexes are formed in both media. The analysis of the pK(a) values for ibuprofen in both the absence and presence of beta-CD (4.12 and 4.66, respectively) suggests that in the inclusion complex the carboxylic group is located outside the cyclodextrin (CD) but interacting with it. Further structural characterization of the complex was carried out by means of am1 semiempiral calculations. Based on the obtained results, a spectrofluorimetric method for the determination of ibuprofen in the presence of beta-CD at 10 degrees C was developed in the range of 4.7-58 mug ml(-1). Better limits of detection (1.6 mug ml(-1)) and quantification (4.7 mug ml(-1)) were obtained in this latter case with respect to those obtained in the absence of beta-CD. The method was satisfactorily applied to the quantification of ibuprofen in pharmaceutical preparations. A novel spectrofluorimetric determination of ibuprofen in the presence of beta-CD was also developed for serum samples at concentration levels between 5 and 70 mug ml(-1). It uses second-order fluorescence excitation-emission matrices coupled to an algorithm based on self-weighted alternating trilinear decomposition (SWATLD), and avoids resorting to separative instrumental analyses.

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Two different spectrofluorimetric methods for the determination of piroxicam (PX) in serum are presented and discussed. One of them is based on the use of three-way fluorescence data and multivariate calibration performed with parallel factor analysis (PARAFAC) and self-weighted alternating trilinear decomposition (SWATLD). This methodology exploits the so-called second-order advantage of the three-way data, allowing to obtain the concentration of the studied analyte in the presence of any number of uncalibrated (serum) components. The method was developed following two different procedures: internal standard addition and external calibration with standard solutions, which were compared and discussed. The second approach investigated is based on the combination of solid-phase extraction (SPE) and room temperature fluorimetry. Both methods here presented yield satisfactory results. The concentration range in which PX could be determined in serum was 1-10 microg ml(-1). The limits of quantification for the experimental solutions using the chemometric approach were 0.09 microg ml(-1) for the standard addition mode and 0.12 microg ml(-1) using external calibration (both for PARAFAC and SWATLD algorithms). In the solid-surface fluorimetric method, the calibration graph was linear up to 0.22 microg ml(-1) and the limit of quantification was 0.02 microg ml(-1).

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Different methods for the determination of naproxen by room-temperature phosphorescence (RTP) using organized media such as cyclodextrins (beta-CD and gamma-CD) and micelles (Triton X-100 and sodium dodecyl sulfate) are reported. The inclusion complexes formed between both beta- and gamma-cyclodextrins and naproxen were previously investigated at both acid and basic pH by spectrofluorimetry. In both cases, 1:1 guest-host stoichiometries were established and the corresponding association constants were calculated. Different systems were examined with the purpose of obtaining phosphorescent emission from naproxen solutions, and the best signals were obtained when naproxen was in the presence of beta-CD-cyclohexane-Tl(I), gamma-CD-1,3-dibromopropane, Triton X-100-Tl(I) and SDS-Tl(I), respectively. In all cases, sodium sulfite was used as deoxygenator. The use of an inorganic compound (thallium nitrate) as a heavy-atom source in a cyclodextrin system represents a novel finding. Surface response optimization approaches were carried out to optimize the chemical variables which have an influence on the RTP emission of naproxen. Based on the results obtained, univariate RTP calibration methods for the determination of the analyte in pharmaceutical preparations were satisfactorily developed. In one case, the standard additions method was applied to a mixture of naproxen and the antibiotic tetracycline.

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The formation constant for a 1:1 binary complex between 6-bromo-2-naphthol (6B2N) and beta-cyclodextrin (CD) in aqueous solution was determined by both absorptimetric and fluorimetric methods. Room-temperature phosphorescence (RTP) was induced by adding small amounts of different apolar liquids as the third component, with cyclohexane producing the strongest enhancement effect. Microcrystals formed in the ternary system seem to be necessary for obtaining phosphorescence emission. The deoxygenation by flowing nitrogen does not improve the RTP signals, while the addition of sodium sulfite as chemical deoxygenant produces quenching of the signals. The calibration graph for 6-bromo-2-naphthol in the presence of beta-CD and cyclohexane was linear for the range of concentrations between 0.04 and 1 mug ml(-1), with a detection limit of 0.04 mug ml(-1).

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The influence of different factors on the room-temperature phosphorescence (RTP) emission from the inclusion complex between alpha-cyclodextrin (alpha-CD) and 6-bromo-2-naphthol (BN) was analyzed. Although RTP signals are detected even in aerated solutions, an efficient enhancement of the phosphorescence emission (about 13 times) is obtained when the solutions of the complex are deaerated with nitrogen bubbling, while quenching is produced when sodium sulfite is used for deoxygenation. Association constants of the 1:1 and 2:1 alpha-CD-BN complexes have been evaluated by molecular absorption and fluorimetric methods. Exciting at 287 nm, the RTP phosphorescence emission showed two maxima located at 500 and 535 nm and a shoulder at 577 nm. The RTP emission increases with the irradiation time of the sample by the xenon lamp of the fluorimeter, until it achieves a constant value after around 10 min of irradiation. The addition of organic molecules such as alcohols and bromoalcohols as a third component of the system produces an enhancement of the RTP emission smaller than that obtained in the absence of them. The calibration graph for BN was linear for the range of concentrations between 0.4 and 2.0 mug ml(-1) with a detection limit of 0.26 mug ml(-1), with relative standard deviation (RSD) (n=6) of 4%, for 1.6 mug ml(-1). The solution was transparent, and there was no precipitation.

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This study focuses on the complex formed between alpha-cyclodextrin (CD) and the anti-inflammatory drug diclofenac in aqueous solution and also on its potential analytical applications. It was corroborated that the fluorescence emission band of diclofenac is significantly intensified in the presence of alpha-CD. From the changes in the fluorescence spectra, it was concluded that alpha-CD forms a 1:1 inclusional complex with diclofenac and its equilibrium constant was calculated to be 1.20(3)x10(3) M(-1). With the purpose of characterizing the inclusion complex, the acid-base behaviour of diclofenac in both the presence and absence of alpha-CD was spectrophotometrically investigated. From the results obtained, it was inferred that both the carboxyl and the secondary amino groups of the guest molecule remain outside the cyclodextrin cavity. Further details on the complex structure was obtained by (1)H NMR measurements and semiempirical calculations. In addition to the analysis of the alpha-CD-diclofenac interaction, a new approach for the quantification of diclofenac in the presence of alpha-CD is described in the range 0-5 mug ml(-1). An application of the method to the determination of the studied drug in pharmaceutical preparations is shown.

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The complexation between beta-cyclodextrin (beta-CD) and piroxicam (PX) was investigated by both fluorescence and absorption spectrometry. A 1:2 guest:host stoichiometry for the complex was established, and its association constant was calculated by applying a non-linear regression method to the changes brought about by the presence of beta-CD in both the fluorescence and absorbance spectra of PX. During the study of the influence of the pH on the fluorescence emission of the complex, an efficient enhancement of the signals at acidic pH was observed. This suggests that the protonated form of PX is included more effectively than the ionized form in the beta-CD cavity. Based on the results obtained, spectrofluorimetric methods for the determination of PX were developed. The best limits of detection and quantification were obtained using beta-CD at an acidic pH. The dynamic range in this latter case was 0.02-1 microgram ml-1. The method was applied satisfactorily to the determination of piroxicam in a pharmaceutical preparation.

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The inclusional complexation between the anti-inflammatory pharmaceutical diclofenac and beta-cyclodextrin (beta-CD) was studied by potentiometry, spectrophotometry and spectrofluorimetry, in both acid and neutral pH. Guest-host 1:1 stoichiometries for the complexes in both media were determined, and their equilibrium constants were calculated. The values obtained from the different methods used are in very good agreement and are in the order of 10(3). From the analysis of the pKa value for diclofenac in both the absence and presence of beta-CD (4.84 and 4.90 respectively), it was inferred that in the inclusion complex the carboxylic group is located outside the cavity. Further structural characterization of the inclusate was carried out by means of 1H NMR spectra and AM1 semiempirical calculations. Based on the obtained results, a spectrofluorimetric method for the determination of diclofenac in the presence of beta-CD was developed in the range of 0-5 micrograms ml-1. Better limits of detection (0.03 microgram ml-1) and quantification (0.1 microgram ml-1) were obtained in this latter case with respect to those obtained in the absence of beta-CD. The method was satisfactorily applied to the quantification of diclofenac in pharmaceutical preparations.

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