A. Guiberteau Cabanillas

Rapid Determination of Sulfathiazole, Oxytetracycline and Tetracycline in Honey by High-Performance Liquid Chromatography

Abstract A simple, rapid and precise analytical method for sulfathiazole, oxytetracycline and tetracycline residues in honey has been established using micellar reversed-phase high-performance liquid chromatography with photometric detection. The mean recoveries of sulfathiazole, oxytetracycline and tetracycline were 97.7, 95.3 and 100.4%, respectively. Detection limits in honey were 0.9 μg/g for sulfathiazole, 1.2 μg/g for oxytetracycline and 3.0 μg/g for tetracycline.

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.

Square wave adsorptive stripping voltametric determination of the mixture of nalidixic acid and its main metabolite (7-hydroxymethylnalidixic acid) by multivariate methods and artificial neural network

Nalidixic acid (NA) and its main metabolite, 7-hydroximethylnalidixic acid (OHNA), are quinolones antibacterial used as agents used for the treatment of urinary tract infection. For both compounds an adsorption process on a hanging mercury electrode (HMDE). On this basis, a square wave adsorptive stripping voltammetry (SWadSV) method has been developed for the individual and simultaneous determination of NA and OHNA. The variables that affect to accumulation process, such as concentration of perchloric acid, accumulation potential and accumulation time have been optimised by using an experimental design (concretely a Box-Behnken design with three levels) together with the response surface methodology (RSM). Calibration curves were linear in the range (0-1.38)x10(-7)molL(-1) for NA and (0-3.23)x10(-8)molL(-1) for OHNA, in the optimized conditions, with detection limits of 9.48x10(-9)molL(-1) and 8.06x10(-10)molL(-1) for NA and OHNA, respectively. The method was applied to urine samples containing only one of the analytes with satisfactory recoveries. As the voltammetric signals of these compounds show a high overlapping, different chemometric methods, such as classical least squares (CLS), partial least squares (PLS), principal component regression (PCR) and artificial neural network (ANN) have been used for the resolution of the mixture. The analysis of these compounds in urine samples were carried out using the different chemometric tools and the best recoveries were obtained by using ANN. No pre-treatment of the sample was necessary.

Simultaneous determination of quinolones for veterinary use by high-performance liquid chromatography with electrochemical detection.

A selective method based on high-performance liquid chromatography with electrochemical detection (HPLC-ECD) has been developed to enable simultaneous determination of three fluoroquinolones (FQs), namely danofloxacin (DANO), difloxacin (DIFLO) and sarafloxacin (SARA). The fluoroquinolones are separated on a Novapack C-18 column and detected in a high sensitivity amperometric cell at a potential of +0.8 V. Solid-phase extraction was used for the extraction of the analytes in real samples. The range of concentration examined varied from 10 to 150 ng g(-1) for danofloxacin, from 25 to 100 ng g(-1) for sarafloxacin and from 50 to 315 ng g(-1) for difloxacin, respectively. The method presents detection limits under 10 ng g(-1) and recoveries around 90% for the three analytes have been obtained in the experiments with fortified samples. This HPLC-ECD approach can be useful in the routine analysis of antibacterial residues being less expensive and less complicated than other more powerful tools as hyphenated techniques.

Determination of fenthion and fenthion-sulfoxide, in olive oil and in river water, by square-wave adsorptive-stripping voltammetry

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO(4). The metabolite gives rise to a peak due to an adsorptive-reductive process at -0.786 V. Fenthion is isolated from olive oil by carrying out a solid-liquid extraction procedure using silica cartridge, followed by a liquid-liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g(-1) and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid-liquid partitioning with trichloromethane. The detection limits are 0.41 ng g(-1) and 0.44 ng g(-1), for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.

Polarographic behaviour and determination of furaltadone in its formulations, milk and urine by differential-pulse polarography

The polarographic behaviour of furaltadone was studied in Britton-Robinson buffer solutions and perchloric acid media. Three well defined reduction waves appear in acidic media (pH < 4) whereas at higher pH the last two peaks overlap. The variation of E1/2 or Ep and Ilim or Ip with pH was studied. The diffusion-controlled nature of the waves at pH 1.87 (Britton-Robinson solution) and in 0.1 M perchloric acid was established and the irreversibility of the electrode process was verified by different criteria. The mechanism for the reduction is discussed. A method for the determination of furaltadone by differential-pulse polarography which allows 0.025–2.0 μg ml−1 (7.7 × 10−8−6.2 × 10−6 M) of this compound to be determined is proposed and was applied to the determination of furaltadone in its formulations, milk and urine.

Determination of Mo(VI) with 2-benzylideneiminobenzohydroxamic acid (2-BIBH) in urine by cathodic stripping voltammetry

SummaryControlled adsorptive accumulation of Mo(VI)-2-BIBH at the hanging mercury drop electrode (HMDE) provides the basis for the direct stripping measurement of Mo(VI) in nanomolar concentration. The cathodic stripping response is evaluated with respect to experimental parameters such as preconcentration time, preconcentration potential and others. A differential pulse cathodic stripping voltammetric method for the determination of Mo(VI) with 2-BIBH in urine is proposed. The detection limit is 10−9 mol/l Mo(VI), standard deviation for 5×10−8 mol/l is ±1.58×10−9 mol/l.

Quantification of Danofloxacin and Difloxacin in Chicken Tissues in the Presence of Sarafloxacin As Interference

A new spectrofluorimetric method has been developed for the quantification of danofloxacin (DANO) and difloxacin (DIFLO), in the presence of the primary metabolite of difloxacin, with sarafloxacin (SARA) as interference, in chicken tissue samples. The method is based on second-order multivariate calibration, applying parallel factor analysis (PARAFAC), to the excitation-emission matrices (EEMs) of these compounds. High overlapping of the signals and influence of matrix effects were observed. To solve the problem, the standard addition method was used. Chemical variables were optimized. The measured EEMs of the analytes, as analytical signals, allowed their quantification in chicken tissue samples. Solid phase extraction was used for the extraction of the analytes in real samples. The range of concentration examined varied from 30 to 100 ng g(-1) for danofloxacin, and from 100 to 200 ng g(-1) for difloxacin. Both analytes can be analyzed individually, and the binary mixture can be resolved, with recoveries comprising between 88.7 and 106.6%.