Teresa Galeano Díaz

Abilities of differentiation and partial least squares methods in the analysis by differential pulse polarography Simultaneous determination of furazolidone and furaltadone

Abstract A comparison between the applicability of two multicomponent analysis methods, differentiation of signals and partial least squares (PLS) methods, to the resolution of overlapping differential pulse polarographic (DPP) peaks corresponding to the irreversible reduction process of two nitrofuran derivatives has been performed. The results show that the derivative DPP signals are not suitable for the resolution of mixtures of these system, by application of the zero-crossing method, because the zero-crossing potential is not independent of the concentration. However, PLS has the capacity of modelling the total evolution of the DPP peaks with the concentration. The PLS multivariate calibration method has been successfully applied to the simultaneous analysis of both compounds in a pharmaceutical formulation.

Resolution of ternary mixtures of nitrofurantoin, furazolidone and furaltadone by application of Partial Least Squares analysis to the differential pulse polarographic signals

The abilities of the Partial Least Squares (PLS) methods in the resolution of ternary mixtures of organic compounds (furaltadone, furazolidone and nitrofurantoin) by using their differential pulse polarographic (DPP) signals are reported. The applicability of these methods to resolve very overlapped peaks whose E(p) also changes with concentration is demonstrated. The analysis of both synthetic and real samples has been made with satisfactory results. The relative error of prediction (REP) is 8.7% for FD, 7.7% for FZ and 6.7% for NF by application of the PLS-2 method.

Square-Wave and Differential Pulse Oxidative Voltammetric Determination of Diquat and Paraquat in Alkaline Medium

Square-wave and differential pulse voltammetric methods are proposed for the determination of the herbicides paraquat and diquat, based on their oxidation peak at the glassy carbon electrode, following their degradation in strong alkaline medium. The potential values are near 0.31 V for paraquat and 0.37 V for diquat in SWV mode and near 0.24 V for paraquat and 0.31 V for diquat in the differential pulse voltammetric (DPV) mode. Once the influence of the chemical conditions and instrumental variables were examined, two different procedures are proposed. The first allows the determination of diquat between 0.05 and 1 µg mL–1, using a 0.05 M sodium hydroxide concentration. In a stronger alkaline medium (1 M sodium hydroxide) both paraquat and diquat can be determined between 1 and 10 µg mL–1. The determination of both compounds is carried out by application of the partial least squares (PLS) type 1 multivariate approach. After optimization of the parameters of the chemommetric procedures, the proposed methods are validated with synthetic samples and applied to determine these herbicides in a commercial formulation containing both compounds and in fortified river water samples.

Stopped flow kinetic-spectrophotometric determination of Diquat in waters

Using the measures of initial reaction rate, a kinetic-photometric method is developed that uses the reaction of Diquat with H2O2 in basic medium. The reaction rate is very high and therefore the stopped-flow mixing technique is required in order to make kinetic measurements. The reaction rate is obtained in 20 s after the reactants are mixed and it allows the simple application of the method proposed to the routine analyses. The sensitivity of the method is very high being the detection limit 0.44 microgmL(-1) and the application range between 1 and 16 microgmL(-1). The time of measure per sample is 90s. The proposed kinetic-photometric method has been applied to the direct determination of this compound in river water, in the water of laundry of the olives, and in a commercial product. The results are very acceptable.

Determination of piceid by photochemically induced fluorescence and second-derivative: Response surface methodology for the optimization of a liquid–liquid extraction procedure for its analysis in wine samples

trans-Piceid itself is weakly fluorescent, but the fluorescence signal (lambda(exc/em)=260/361nm) is greatly enhanced by UV-irradiation of its hydroethanolic solutions. Employing the photoinduced emission signal at 361nm or the amplitude of the second-derivative-photoinduced emission spectrum, between 353 and 361nm, a linear relation is found in the assayed range 5.7-31.4ngmL(-1) of trans-piceid and limits of detection of 1.7 and 2.1ngmL(-1), respectively, are obtained. A previous liquid-liquid extraction is necessary for the determination of piceid in wine. Experimental design (Central Composite Design) together with the Response Surface Methodology have been used to find optimum conditions for the extraction procedure. For this purpose, the difference between the photoinduced-fluorescence signal (lambda(exc/em)=260/361nm) of the aqueous phase, before and after being extracted, has been considered as Response Function. A tartrate buffer (pH 5.0) concentration of 0.15molL(-1) and a phase ratio of 1 are determined as optimum conditions. The amplitude of the second-derivative-emission spectrum, corresponding to the evaporated and re-dissolved organic phase, between 353 and 361nm has been employed as analytical signal. Standard addition method has been applied to the analysis of piceid in different wine samples under optimum conditions. Results of wine analysis have been satisfactorily validated by HPLC.

Determination of 1-naphthylamine and the related pesticides, naptalam and antu, in river-water by high-performance liquid chromatography. Application to the study of the degradation processes of naptalam

A method is described for the determination of 1-naphthylamine and the related pesticides, naptalam and antu, in river-water by high-performance liquid chromatography. A Nucleosil 5 C18 100A (25 × 0.46 cm) column is used, and a mobile phase of water–(0.1% acetic acid)–acetonitrile, which was found to be the optimum for this determination. Photometric detection is conducted at 220 nm. Preconcentration on C18 Sep-Pak cartridges has been used to determine these compounds in river-water, with good recoveries. A study of the degradation processes of naptalam to 1-naphthylamine and N-1-naphthylphthalimide is also described.

Semiautomatic determination of furazolidone and furaltadone by continuous and stopped flow FIA methods

New methods are proposed for the semiautomatic determination of furazolidone and furaltadone by photometric flow injection or stopped flow FIA analysis, on the basis of their alkaline hydrolysis reactions. Linear calibration graphs between 1 and 30 μg/ml are obtained for both compounds, the detection limits for furazolidone and furaltadone being 0.20 and 0.26 μg/ml, respectively, by flow injection and 0.27 and 0.21 μg/ml by the stopped flow approach.

Characterization of Spanish Paprika by Multivariate Analysis of Absorption and Fluorescence Spectra

ABSTRACT Spanish paprika was clustered on the basis of the Spanish Protected Designation of Origin “Pimentón de La Vera” by molecular absorbance and fluorescence with principal component analysis and parallel factor analysis. Rapid extraction of carotenoids, capsaicinoids, and tocopherols was optimized; the best conditions included ethanol as the extractant, an extraction time of 10 min in an ultrasonic bath, and a sample size of 0.1 g. The procedure provided good precision with a relative standard deviation of 1.2% for four samples. Molecular absorption spectra were obtained from 250 to 600 nm and fluorescence excitation and emission spectra were collected from 200 to 295 nm and 300 to 400 nm, respectively. Forty-eight “Pimentón de La Vera” paprika samples and 19 samples from other origins were characterized. A principal component analysis model was constructed from the absorption spectra and clustering was obtained based on the origin. Parallel factor analysis was performed on the fluorescence data and better characterization of the origin was obtained.

Multiresidue method for the control of pesticide residues in tomatoes and derived products

A new multiresidue method, intended for the routine analysis of 60 multi-class pesticides in tomatoes and derived products, has been developed. The method uses gas chromatography, with a large volume injection system and tandem mass spectrometry detection (LVI-GC-MS-MS). The pretreatment of the samples is fast and simple, as the pesticide residues are extracted from the sample with ethyl acetate in presence of NaHCO3 and anhydrous Na2SO4, without additional clean-up steps and, consequently, with cost and time saving benefits. The method presents appropriate selectivity and good sensitivity with limits of quantification (LOQs) between 0.5 and 20 μg kg−1, which are lower than the maximum residue levels established by several regulatory legislation. Average recoveries between 70 and 115%, with a relative standard deviation lower than 20% in all cases, and good linearity were obtained in the studied concentration range. For the routine analysis, a quality control system was applied to avoid false positive and false negative results.