Juan A. Arancibia

Spectrofluorimetric determination of diclofenac in the presence of α-cyclodextrin

Abstract This study focuses on the complex formed between α-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 α-CD. From the changes in the fluorescence spectra, it was concluded that α-CD forms a 1:1 inclusional complex with diclofenac and its equilibrium constant was calculated to be 1.20(3)×103 M−1. With the purpose of characterizing the inclusion complex, the acid–base behaviour of diclofenac in both the presence and absence of α-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 1H NMR measurements and semiempirical calculations. In addition to the analysis of the α-CD–diclofenac interaction, a new approach for the quantification of diclofenac in the presence of α-CD is described in the range 0–5 μg ml−1. An application of the method to the determination of the studied drug in pharmaceutical preparations is shown.

Complexation study of diclofenac with β-cyclodextrin and spectrofluorimetric determination

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.

Chemometrics-Assisted Excitation−Emission Fluorescence Spectroscopy on Nylon Membranes. Simultaneous Determination of Benzo[a]pyrene and Dibenz[a,h]anthracene at Parts-Per-Trillion Levels in the Presence of the Remaining EPA PAH Priority Pollutants As Interferences

This work presents a novel approach for the simultaneous ultratrace determination of benzo[ a]pyrene and dibenzo[ a,h]anthracene, the two most carcinogenic polycyclic aromatic hydrocarbons (PAHs), in a very interfering environment, combining the recently discovered ability of the nylon membrane to strongly retain and concentrate PAHs on its surface, the sensitivity of molecular fluorescence, and the selectivity of second-order chemometric algorithms. The fluorescence excitation-emission matrices, directly measured on a nylon-membrane surface, are processed by applying parallel factor analysis (PARAFAC) and unfolded partial least-squares coupled to residual bilinearization (U-PLS/RBL). The superiority of U-PLS/RBL to quantify BaP and DBA at concentrations below 10 ng L (-1) in the presence of the remaining 14 US EPA (United States Environmental Protection Agency) PAHs at total concentrations ranging from 1400 and 14,000 ng L (-1) is demonstrated. The present method successfully faces this complex challenge without using organic solvents, which are to known produce environmental contamination. Finally, the high sensitivity of the present method avoids preconcentration and elution steps, considerably decreasing the analysis time and the experimental errors. Because the instrumental involved in the determination is nonsophisticated, the experiments could be carried out in routine laboratories.

A review on second- and third-order multivariate calibration applied to chromatographic data

Quantitative analytical works developed by processing second- and third-order chromatographic data are reviewed. The various modes in which data of complex structure can be measured are discussed, with chromatographic separation providing either one or two of the data dimensions. This produces second-order data (matrices from uni-dimensional chromatography with multivariate detection or from two-dimensional chromatography) or third-order data (three-dimensional data arrays from two-dimensional chromatography with multivariate detection). The available algorithms for processing these data are classified and discussed, regarding their ability to cope with the ubiquitous phenomenon of retention time shifts from run to run. A summary of relevant works applying this combination of techniques is presented, with focus on quantitative analytical results. Special attention is paid to works achieving the full potentiality of the multidimensional data, i.e., the second-order advantage.

Non-Trilinear Chromatographic Time Retention−Fluorescence Emission Data Coupled to Chemometric Algorithms for the Simultaneous Determination of 10 Polycyclic Aromatic Hydrocarbons in the Presence of Interferences

Multivariate calibration coupled to high-performance liquid chromatography-fast scanning fluorescence spectroscopy (HPLC-FSFS) was employed for the analysis of 10 selected polycyclic aromatic hydrocarbons (PAHs), six of which correspond to heavy PAHs. The goal of the present study was the successful resolution of a system even in the presence of real interferences. Second-order HPLC-FSFS data matrices were obtained in a short time with a chromatographic system operating in isocratic mode. The difficulties in aligning chromatographic bands in complex systems, such as the ones presented here, are discussed. Two second-order calibration algorithms which do not require chromatographic alignment were selected for data processing, namely, multivariate curve resolution-alternating least-squares (MCR-ALS) and parallel factor analysis 2 (PARAFAC2). These algorithms did also achieve the second-order advantage, and therefore they were able to overcome the problem of the presence of unexpected interferences. The study was employed for the discussion of the scopes of the applied second-order chemometric tools, demonstrating the superiority of MCR-ALS to successfully resolve this complex system. The quality of the proposed techniques was assessed on the basis of the analytical recoveries from different types of water and olive oil samples after solid-phase extraction. The studied concentration ranges in water samples were 5.6 x 10(-3)-0.20 ng mL(-1) for heavy PAHs and 0.036-0.80 ng mL(-1) for light PAHs, while in oil samples the PAHs concentrations were 0.13-9.6 and 2.3-49.5 ng mL(-1) for heavy and light PAHS, respectively. All real samples were analyzed in the presence of the studied interferences.

Determination of five pesticides in juice, fruit and vegetable samples by means of liquid chromatography combined with multivariate curve resolution

The aim of this work was to quantify five commonly used pesticides (propoxur, carbaryl, carbendazim, thiabendazole and fuberidazole) in real samples as: tomato, orange juice, grapefruit juice, lemon and tangerine. The method used for the determination of these analytes in the complex matrices was high-performance liquid chromatography with diode array detection. In order to work under isocratic conditions and to complete each run in less than 10 min, the analysis was carried out applying multivariate curve resolution coupled to alternating least-squares (MCR-ALS). The flexibility of this applied multivariate model allowed the prediction of the concentrations of the five analytes in complex samples including strongly coeluting analytes, elution time shifts, band shape changes and presence of uncalibrated interferents. The obtained limits of detection (in μg L(-1)) using the proposed methodology were 2.3 (carbendazim), 0.90 (thiabendazole), 12 (propoxur), 0.46 (fuberidazole) and 0.32 (carbaryl).

Second-order multivariate calibration procedures applied to high-performance liquid chromatography coupled to fast-scanning fluorescence detection for the determination of fluoroquinolones

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%.

Screening of oil samples on the basis of excitation-emission room-temperature phosphorescence data and multiway chemometric techniques. Introducing the second-order advantage in a classification study.

Room-temperature phosphorescence excitation-emission matrices and multiway methods have been analyzed as potential tools for screening oil samples, based on full matrix information for polyaromatic hydrocarbons. Crude oils obtained from different sources of similar geographic origin, as well as light and heavy lubricating oils, were analyzed. The room-temperature phosphorescence matrix signals were processed by applying multilayer perceptron artificial neural networks, parallel factor analysis coupled to linear discriminant analysis, discriminant unfolded partial least-squares, and discriminant multidimensional partial least-squares (DN-PLS). The ability of the latter algorithm to classify the investigated oils into four categories is demonstrated. In addition, the combination of DN-PLS with residual bilinearization allows for a proper classification of oils containing unsuspected compounds not present in the training sample set. This second-order advantage concept is applied to a classification study for the first time. The employed approach is fast, avoids the use of laborious chromatographic analysis, and is relevant for oil characterization, identification, and determination of accidental spill sources.

A novel application of nylon membranes to the luminescent determination of benzo[a]pyrene at ultra trace levels in water samples

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.

Determination of naproxen in pharmaceutical preparations by room-temperature phosphorescence. A comparative study of several organized media

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.