A. Muñoz de la Peña

Rhodamine and BODIPY chemodosimeters and chemosensors for the detection of Hg2+, based on fluorescence enhancement effects

Fluorescent sensors for Hg2+ are demonstrating their potential in a variety of fields such as environmental and biological applications. The review focuses on the recent development of rhodamine derivatives in which the spirolactam (non-fluorescent) to ring-opened amide (fluorescent) process was utilized and on the development of BODIPY derivatives in which the photoinduced electron transfer (PET) process was utilized. New trends in the immobilization of the molecular probes on solid supports, as polymers and/or nanostructures, have been emphasized. The different recognition mechanisms used for the signal responses have been analyzed. The spectroscopic properties, reaction media, analytical parameters, interferences by other ions and practical applications have been summarized.

Analysis of antibiotics in fish samples

The use of antibiotics in food-producing animals has generated considerable interest because the widespread administration of these drugs may lead to the development of resistant human pathogens. A large increase in the demand for seafood products has occurred in the last century. This has led to a concomitant increase in high-intensity aquaculture methods, characterized by high stock density and volume, and the heavy use of formulated feeds containing antibiotics, among other substances. Therefore, accurate and sensitive determination of antibiotic residues is now a necessity. In order to protect human health, the European Union and other regulatory authorities worldwide have established maximum residue limits (MRL) for antibiotic residues in animal products entering the human food chain. This paper reviews the most recent methods for analysis of antibiotic residues in fish.

Cyclodextrin-induced fluid solution room-temperature phosphorescence from acenaphthene in the presence of 2-bromoethanol

Abstract A 1:1 stoichiometric ratio and a formation constant of 130 1 mol −1 were obtained for the binary inclusion complex between acenaphthene and β-cyclodextrin (CD). On addition of 2-bromoethanol, effective quenching of the fluorescence emission and enhancement of the room-temperature phosphorescence (RTP) of acenaphthene is observed. The use of 2-bromoethanol as an external “heavy atom” to obtain room-temperature phosphorescence in fluid solutions is discussed. The RTP emission from acenaphthene included in β-CD was optimized and characterized. The apparent formation constant of the ternary associate was determined to be 880 1 mol −1 by the use of RTP enhancement in the presence of 1% 2-bromoethanol. The data indicate a ternary association between acenaphthene, β-CD and the bromo alcohol. The use of sodium sulfite, for chemical deoxygenation, to obtain RTP emission from a non-heavy atom-containing luminophor is shown to be feasible. The kinetics of the deoxygenation reaction were established and a photochemical catalytic effect on the reaction was demonstrated.

Simultaneous determination of 2-furfuraldehyde, 5-hydroxymethylfurfuraldehyde and malonaldehyde in mixtures by derivative spectrophotometry and partial least-squares analysis

Abstract 2-Furfuraldehyde, 5-hydroxymethylfurfuraldehyde and malonaldehyde are known to react with 2-thiobarbituric acid when heated in an acidic medium. A study of the influence of several chemical and physico-chemical variables on the reaction was undertaken. The products of reaction show high absorption in the visible spectral region with several degrees of overlapping. The resolution of ternary mixtures of these compounds was accomplished by several chemometric approaches. A comparative study of the results obtained for simultaneous determinations in mixtures by using derivative spectrophotometry and partial least-squares analysis is presented. The multi-wavelength factor analysis-based method is demonstrated to be the method of choice for the multi-component analysis of ternary mixtures of these compounds.

Monitoring of phenylurea and propanil herbicides in river water by solid-phase-extraction high performance liquid chromatography with photoinduced-fluorimetric detection.

The separation and determination of five herbicides, including propanil and the phenylureas diuron, isoproturon, linuron and neburon, has been performed by an HPLC method, using photochemically-induced fluorescence detection. The non-fluorescent herbicides were transformed into fluorescent compounds by post-column photochemical reaction. A 60:40 (v/v) acetonitrile-buffer solution of potassium phosphate dibasic (pH 7, 0.01 M) was used for the chromatographic elution to separate propanil, linuron and neburon. The overlapping of isoproturon and diuron peaks, in the selected conditions, was resolved by changing the initial movil phase composition to 50:50 (v/v) methanol-buffer solution of potassium phosphate dibasic (pH 7, 0.01 M). The procedure was applied with satisfactory results to the analysis of these herbicides in Guadiana river water samples (Badajoz, Spain), allowing the detection of herbicide residues in the order of mug l(-1), by using a solid-phase extraction (SPE) pre-concentration step.

Partial least squares multicomponent fluorimetric determination of fluoroquinolones in human urine samples

Ternary mixtures of fluoroquinolones, with a 7-piperazinyl substituted group have been simultaneously determined in human urine samples by application of a multivariate calibration partial least squares (PLS) model. The calibration set was designed with 15 urine samples containing different concentrations of the three fluoroquinolones and 16 blank urine samples. The concentration range for the fluoroquinolones were up to 25ngml(-1) for norfloxacin (NOR), 80ngml(-1) for ofloxacin (OFLO) and 300ngml(-1) for enoxacin (ENO). The method is based on the native fluorescence emission of these compounds in sodium dodecyl sulfate (SDS) medium, at pH 4.0, when exciting at 277nm. A selection of the emission wavelength range used for the analysis was made for each component. Intraday and interday precision values were determined. Figures of merit as selectivity, sensitivity, limit of detection (LOD) and analytical sensitivity were also calculated. Using the standard addition methodology, five urine samples from five different persons, fortified with three concentration levels of the fluoroquinolones, were analyzed. The limits of detection in urine were 10.0, 0.5 and 0.8ngml(-1) for ENO, NOR and OFLO, respectively.

Determination of fluoroquinolones in urine and serum by using high performance liquid chromatography and multiemission scan fluorimetric detection.

A high performance liquid chromatography (HPLC) method has been developed for the simultaneous determination of four fluoroquinolones. The studied compounds have been enoxacin (ENO), norfloxacin (NOR), ofloxacin (OFLO) and enrofloxacin (ENRO). An isocratic elution method, using a mixture of tetrahydrofuran (8%) and phosphate buffer (pH 3.00, 30.0mM, 92%) as mobile phase, has been developed. Fluorimetric detection, exciting at 277nm, and multiemission scan (407nm for ENO, 444nm for both NOR and ENRO and 490nm for OFLO) has been used. Detection limits of 500, 14.7, 25.2 and 15.0ngmL(-1) for ENO, NOR, OFLO and ENRO, respectively, have been obtained. The proposed method has been satisfactorily applied to analyze NOR, OFLO and ENRO in human urine and serum samples.

Absorptiometric and spectrofluorimetric study of the inclusion complexes of 2-naphthyloxyacetic acid and 1-naphthylacetic acid with β-cyclodextrin in aqueous solution

The inclusion complexes of 2-naphthyloxyacetic acid (NOA) and 1-naphthylacetic acid (NAA) with β-cyclodextrin have been investigated in aqueous solution. It has been demonstrated that the naphthalene derivatives form 1:1 complexes when included in the cyclodextrin. A possible structure is proposed, having an axial inclusion of the naphthalene derivatives. In the case of the β-CD: NOA complex, the naphthyl moiety is included in the cyclodextrin and the acetic acid group protrudes from the cavity, while NAA is only partially included because of the steric effect of the group in position 1. Association constants of 560±100 M−1 and 100±50 M−1 have been calculated for the β-CD: NOA and β-CD: NAA complexes, making use of the increment in the fluorescene emission produced in the inclusion process.

Simultaneous determination of pesticides by multivariate spectral analysis and derivative spectrophotometry

Abstract The quantitative predictive abilities of derivative spectral analsis by using the zero-crossing point method are compared with the results obtained by the use of a multivariate calibration method. Mixtures of two pesticides (carbaryl and chlorpyrifos) were resolved of derivative spectrophotometry. Partial least squares (PLS), a full spectrum calibration method, was also applied with previous optimization of the calibration matrix by the PLS-2 method. Both approaches were satisfactorily applied to the simultaneous determination of carbaryl and chlorpyrifos in commercial formulations. The simplicity of the derivative method makes it the method of choice for simple binary mixtures.

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%.