F. Salinas

Simultaneous determination of sulfadiazine, doxycycline, furaltadone and trimethoprim by partial least squares multivariate calibration

Quaternary and ternary mixtures of doxycycline (DX), sulfadiazine (SD), furaltadone (FT) and trimethoprim (TM) were determined by application of a multivariate calibration model. Partial least squares (PLS) methods were applied. The optimized model allowed the simultaneous determination of DX, SD, FD, and TM in artificial mixtures and in milk, and also, the simultaneous determination of SD, FT and TM in artificial mixtures and in a veterinary formulation.

Indirect voltammetric determination of carbaryl and carbofuran using partial least squares calibration

Abstract A differential pulse voltammetric method is proposed for the determination of the carbamate pesticides carbaryl and carbofuran, based on the anodic peaks observed following their alkaline hydrolysis (formation of phenol derivatives). Linear relationships between the oxidation peaks and concentration were obtained in the ranges 5 × 10 −7 to 10 −4 M for carbaryl and 5 × 10 −7 to 5 × 10 −5 M for carbofuran, the relative standard deviations being 1.62 and 1.86%, respectively. The method was applied to the determination of these compounds in formulations. Different chemometric methods (PLS-1, PLS-2 and CLS) were examined for the resolution of the overlapped peaks of both compounds and their determination in mixtures. The best results were obtained with the PLS-1 method, which was applied to determine both compounds in river water samples.

Study and determination of the pesticide Imidacloprid by square wave adsorptive stripping voltammetry

An electroanalytical method has been developed for the detection and determination of the pesticide 1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2ylidineamine (Imidacloprid) by square wave adsorptive stripping voltammetry on a hanging mercury drop electrode (HMDE) in aqueous solution with Britton-Robinson buffer as supporting electrolyte. The best adsorption conditions were found to be pH 7.2, an accumulation potential of -1050 mV (HMDE vs. Ag/AgCl-KCl 3M) and an accumulation time of 50 s. Effects of square wave frequency, step potential and pulse amplitude were examined for the optimization of instrumental conditions. Calibration curve is linear in the range 2 x 10(-8)-5 x 10(-7) M with a detection limit of 1.6 x 10(-8) M (Clayton et al. method). The method is applied to the direct determination of the pesticide in river water samples. For a concentration of 4.1 x 10(-8) M a recovery value of 104+/-3% is obtained. In order to determine lower concentrations, previous preconcentration and cleaning steps (liquid-liquid extraction into CH(2)Cl(2) and solid-phase extraction with Sep-Pak C(18) cartridges) are carried out. The recovery values obtained in spiked river water are 89+/-4% for 2 x 10(-8) M and 90+/-6% for 8 x 10(-9) M.

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.

Polarographic behaviour of sulfadiazine, sulfamerazine, sulfamethazine and their mixtures. Use of partial least squares in the resolution of the non-additive signals of these compounds

The polarographic behaviour of the sulfonamides sulfadiazine, sulfamerazine and sulfamethazine was studied in Britton–Robinson buffer solutions. These compounds show well defined reduction waves and differentiated peaks in differential-pulse polarography (DPP) with Ep values near –700, –790 and –1140 mV, respectively, in an acidic medium (approximately pH 2), the behaviour of the sulfonamides in response to variations in pH and concentration is very similar. However, when two or three of these compounds are present together, the signal obtained in DPP does not agree with the superposition of the signal of each one of them when present alone. This fact can be explained by the change that the dc wave corresponding to any of the sulfonamides undergoes owing to the presence of one or two of the others, thus making the direct analysis of their mixtures by DPP impossible. The ability of partial least squares multivariate methods to resolve this problem was examined. In general, good results were obtained and the method was applied to the analysis of mixtures of these sulfonamides in veterinary and pharmaceutical formulations.

Voltammetric Behavior and Simultaneous Determination of the Antioxidants Propyl Gallate, Butylated Hydroxyanisole, and Butylated Hydroxytoluene in Acidic Acetonitrile-Water Medium Using PLS Calibration

The voltammetric behavior of propyl gallate (PG), butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) has been studied at the glassy carbon electrode (static and rotating), in an acetonitrile-water medium using LS, sampled DC, DP and cyclic voltammetry. The use of a Britton-Robinson buffer (pH 2.8) containing 20 % of acetonitrile together with the sampled DC mode allows one to analyze binary and ternary mixtures of these antioxidants by applying a PLS type 1 multivariate approach. After optimization of the parameters of the chemometric procedure, the proposed method was validated with synthetic samples and applied for the determination of these antioxidants in different spiked samples of packet soup.

Determination of nitrofurantoin, furazolidone and furaltadone in milk by high-performance liquid chromatography with electrochemical detection

A HPLC method with coulometric detection has been established to carry out the separation of the three nitrofuran derivatives, nitrofurantoin, furazolidone and furaltadone. A Nova-Pak C18 column (150 x 3.9 mm) and a Coulochem II detector from ESA have been used. After obtaining the hydrodynamic curves of the three compounds in the porous graphite electrode a potential of -600 mV was selected as the working potential. The influence of other variables such as mobile phase composition and flow-rate were studied. The mobile phase considered as an optimum was acetonitrile-0.1 M aqueous solution of sodium perchlorate (28:72), with 0.5% glacial acetic acid. The oxygen of the mobile phase was removed with a vacuum system on-line and a nitrogen stream was used to remove the oxygen of the samples. The calibration graphs and the detection limits were established. The method proposed was used, with good results, for the determination of the three compounds in milk.

Determination of binary mixtures of sulfonamides by photochemically induced fluorescence using partial least squares multivariate calibration

Binary mixtures of sulfamethazine (SMTZ), sulfamerazine (SMRZ) and sulfadiazine (SDZ) were determined by room-temperature photochemically induced fluorescence. The resolution was accomplished by partial least squares (PLS) multivariate calibration. The fluorescence intensity of these heterocyclic sulfonamides was measured after ultraviolet irradiation for 12 min. The photoproducts obtained showed analytically useful fluorescence signals when an excitation wavelength of 284 nm was used. PLS was applied with previous optimization of the calibration matrix by the PLS-1 method. The multivariate factor analysis based calibration method allowed the simultaneous determination of SMTZ–SMRZ, SMTZ–SDZ and SMRZ–SDZ mixtures.

Photochemical-spectrofluorimetric method for the determination of benzoylurea insecticides : applications in river water samples and in technical formulations

Ultraviolet (UV) irradiation was used to obtain fluorescent photoproducts from four non-fluorescent benzoylurea (BU) insecticides (flufenoxuron (FLF), lufenuron (LUF), hexaflumuron (HF) and triflumuron (TRF)). The effect of solvent, pH (in aqueous solutions), organic solvent percentage and UV irradiation time on the excitation and emission wavelengths and fluorescence intensity were investigated. The largest fluorescence signals and the shortest UV irradiation time were obtained in methanol, ethanol and 2-propanol. Linear calibration graphs were established in the interval between 0.025 and 1.000 microg ml(-1) from FLF and TRF and between 0.050 and 1.000 microg ml(-1) from LUF and HF with regression coefficients larger than 0.99. A method based on the use of the first-derivative of the spectra of photoproducts was applied to the determination of BU insecticides in river water samples and in technical formulations. The mean recoveries ranged from 95.0% to 110.0% in river water samples and from 92.0% to 101.0% in technical formulations, according to the compound. A preconcentration step, using LLE, allowed to reach the concentration levels established by the EU directive for pesticides in drinking water.

Comparison of chemometric methods : Derivative ratio spectra and multivariate methods (CLS, PCR and PLS) for the resolution of ternary mixtures of the pesticides carbofuran carbaryl and phenamifos after their extraction into chloroform

The resolution of a ternary mixture of the pesticides carbofuran, carbaryl and fenamiphos in heterogeneous media (after extraction into CHCl 3 ) by the application of different chemometric methods such as derivative ratio spectra (DD), classical least squares (CLS), principal components regression (PCR) and partial least squares (PLS) was performed. CLS, PCR and PLS were applied with the absorption spectra or with their transformations (logarithm or first or second derivative). Also, different data preprocessing algorithms were examined. Second-derivative spectra were used for DD. A comparison of the results obtained in the analysis of these compounds by the different methods was made by using analysis of variance (ANOVA). These methods were successfully applied to the analysis of spiked river water samples.