RESUMEN

A polarographic study about how three anti-inflammatories, such as Aceclofenac, Tenoxicam and Droxicam behave, using tast polarography (TP) and differential pulse polarography (DPP) was carried out. These studies were always carried out in a media formed by Methanol-Britton-Robinson aqueous buffer (0.1M) (4:96 (v/v)) due to the low solubility of these drugs in water. A strong influence of pH on analytical signals was observed, showing that the optimal pH values were between 4 and 5. Using DPP in the optimal experimental conditions, a detection limit of 10 ppb for Tenoxicam and Droxicam and 52 ppb for Aceclofenac was reached. The DPP proposed method was successfully applied to the determination of the active compounds in commercial drugs.

Asunto(s)

Antiinflamatorios no Esteroideos/análisis , Diclofenaco/análogos & derivados , Diclofenaco/análisis , Metanol/química , Piroxicam/análogos & derivados , Piroxicam/análisis , Polarografía/métodos , Piridinas/análisis , Agua/química , Antiinflamatorios no Esteroideos/química , Antiinflamatorios no Esteroideos/normas , Diclofenaco/química , Diclofenaco/normas , Piroxicam/química , Piroxicam/normas , Piridinas/química , Piridinas/normas , Control de Calidad , Solubilidad

RESUMEN

Differential pulse polarography (DPP) and square wave voltammetry (SWV) were investigated, in order to know the stability of solid propellants which contain diphenylamine. The simultaneous determination of N-nitrousdiphenylamine (NnDPA), 2-nitrodiphenylamine (2nDPA), 4-nitrodiphenylamine (4nDPA) and 2,4-dinitrodiphenylamine (2,4dnDPA) by DPP and SWV was proposed due to these nitro-derivatives appear during the stabilisation process from degradation of diphenylamine (DPA) used as stabiliser in propellant compositions. The proposed methods were successfully applied to the simple base solid propellant (with nitrocellulose as the only active component), with its stabiliser DPA. In all cases and with both the techniques, detection limits

RESUMEN

A kinetic study of the hydrolytic decomposition of droxicam was carried out in order to establish the possible pharmacological action of the drug in the organism of the human being. The electrochemical technique used was scan cyclic voltammetry on a HMDE, giving a well-defined peak. Due to the insolubility of droxicam in water, the working media was a methanol-H(2)O (4:96, V/V) mixture. The decomposition product of droxicam is piroxicam, which is also reduced on a mercury electrode giving a well-defined cyclic voltammetric peak. It is proposed that the decomposition of droxicam is controlled by a kinetic equation: v=(1.93 x 10(-3)+78.9 [D]) [D]=k(D)[D].

Asunto(s)

Antiinflamatorios no Esteroideos/química , Piridinas/química , Electroquímica , Concentración de Iones de Hidrógeno , Cinética , Metanol/química , Solubilidad , Agua/química

RESUMEN

A polypyrrole electrode modified with a tetrasulfonated nickel(II) phthalocyanine complex (GCE/PPy/NiPcTs) was used as amperometric electrochemical detector in a flow injection system, in order to determine some antioxidants in foods. The lather were separated by HPLC and detected at the modified electrode. Previous investigations carried out in our laboratory employed this electrode and cyclic voltammetry (CV), obtaining excellent results, due to an electrocatalytic effect on the oxidation of certain alimentary antioxidants, such tert-butylhydroquinone (TBHQ), 3-tert-butyl-4-hydroxyanisole (BHA) and propylgallate (PG). In order to obtain good separation, the chromatographic conditions were optimised. The geometry of the flow injection analysis (FIA) circuit and the reproducibility of the results were also optimised and, finally, the linear relationship between the signal and the concentration was verified. The proposed procedure is more precise and accurate than the conventional voltammetry methods. These results offer new analytical possibilities to this type of modified electrodes. The developed methods were applied to the determination of these antioxidants in commercial food.

RESUMEN

The voltammetric behaviour of the antioxidants 3-tert-butyl-4-hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ), at a polymer electrode modified with nickel phthalocyanine as electron mediator, is described, and an electroanalytical method for the determination of these antioxidants based on their electrochemical oxidation on the modified electrode is proposed. Cyclic voltammograms showed well-defined oxidation peaks slightly shifted towards less positive potentials with respect to those obtained at the platinum disk electrode for both antioxidants. The peak currents measured at the modified electrode are considerably higher than those obtained at the unmodified electrode. A scan rate of 100 mV s(-1), a minimum methanol percentage of 0.5% and a 0.1-M Britton-Robinson medium were chosen as working conditions. The obtained results suggest that the BHA oxidation produces the TBHQ reduction product. This product is oxidised during the second cyclic scan, to generate the mentioned TBHQ as final product. These studies also reveal that sensitive response for both antioxidants can be obtained by using the differential pulse voltammetry (DPV) technique. Responses observed are dependent on the nature of the control solution (% methanol and pH) and the nature of voltammetric conditions (potential amplitude, DeltaE, and scan rate, v(b)). These factors have been modified in order to find the best analytical conditions. The mutual interferences between both antioxidants and the measurement reproducibility were tested. Using cyclic voltammetry (CV) and differential pulse voltammetry, BHA and TBHQ linear calibration graphs were obtained. The detection limits were 2.1 ppm for both when CV was used, and 18.7 ppm (BHA) and 1.23 ppm (TBHQ) for DPV. The developed methods were applied to the determination of BHA in spiked glaze biscuits and TBHQ in spiked mushroom cream.

RESUMEN

In this paper a study of the electrocatalytic oxidation of propylgallate (PG) by using a polypyrrole electrode modified with tetrasulfonate nickel (II) phthalocyanine complex (Pt/PPy/NiPcTs) was carried out. Several parameters of this polymeric electrode, such as: (a) its stability in hydroorganic solution, by using an indium tin oxide (ITO) electrode and spectrophotometry; and (b) its thickness using electrochemical techniques, have been studied. In addition, several parameters affecting the PG voltammetric peak, such as pH, methanol water ratio, potential scan rate and analyte concentration, were considered. Finally, the developed method was applied to the determination of PG in spiked potato flakes and cornflakes, showing its validity.

RESUMEN

An electroanalytical method for determination of the anti-inflammatory agent aceclofenac at the ppb level using adsorptive stripping voltammetric techniques on conventional and surfactant chemically modified electrodes is developed. In this electroanalytical study a process of aceclofenac adsorption on carbon particles has been identified. In order to improve the aceclofenac determination, a chemical modification of the carbon paste was carried out employing several hydrophobic substances such as phospholipid and fatty acids, as well as several surfactants such as the non-ionic Triton X-100 and Triton X-405 and anionic sodium dodecyl sulfate. The influence of parameters such as pH, preconcentration time, carbon Nujol ratio, surfactant carbon ratio, potential scan rate, etc., on sensitivity of the method were widely studied. The proposed method was applied to the determination of the active compound in tablets.

RESUMEN

A method for piroxicam determination based on adsorptive stripping voltammetric techniques, using conventional and chemically modified carbon paste electrodes in micellar media, is described. The employed surfactants were sodium dodecyl sulfate (SDS), Triton X-100, Triton X-405, Tween 80 and Brij 30. However, the purpose of this paper is, at present, to research the use of surfactants as carbon paste modifier because one of the mechanisms of hydrophobic drugs ad-accumulation on the carbon paste electrode is based on the chemical affinity. Besides, because of the water piroxicam insolubility, a special aqueous medium, such as a surfactant solution above its c.m.c. was used, this micellar media being very advantageous in relation to the use of organic or aqueous-organic media, in order to dissolve the studied drug and to remove the problems derived from the organic solvents use. In addition, a piroxicam ad-accumulation increase, on surfactant modified carbon paste electrode, with the surfactant mass incorporated into the electrode, was observed.