Desenvolvimento de célula espectroeletroquímica em fluxo e sua aplicação analítica ao estudo e a determinação de derivados fenotiazínicos / Development of spectrolectrochemical flow cell and its analytical application to the study and the determination of phenothiazinics derivatives

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The present work is concerned with the enhancement and assessment of a novel long-optical-path spectroelectrochemical cell for in situ spectrophotometric detection in the ultraviolet and visible range, optimised for flowing operation, especially under FIA (Flow Injection Analysis) conditions. The sensitive and rather selective monitoring of electrolysed species present at the electrode-solution interface, together with simplicity of assembly and adaptation to existing commercial equipments, were some of the features targeted in the cells improvement. The use of Au-film electrodes obtained from certain types of recordable CDs (Compact Disc-Recordable), attached onto acrylic supports in turn accommodated directly in conventional 1-cm optical-path cuvettes, makes the production of this cell cheaper than any other model so far proposed. O-tolidine and potassium hexacyanoferrate were employed as model systems for the assessment of instrumental parameters such as applied potential, flow rate, injected volume, repeatability and concentration range of the analyte, aiming at establishing the best working conditions for its application in analytical chemistry. High optical sensitivity, stable and reproducible operation, as well as the possibility of functioning either in the stationary or in flow modes, thus with the advantage of exploiting the FIA methodology, are some of the features observed for the cell. Further to highlighting the cellpotentials and in order to seek a better understanding of the processes involved, the oxidation mechanism of a few phenothiazinic derivatives was investigated. Prometazine, promazine and chlorpromazine were comparatively studied in different media. The combination of the electrochemical and spectroscopic information obtained in situ contributed for a better comprehension of the mechanisms involved and revealed that the structure of the side chain is the key factor in the formation of the oxidation products, although the difference in the electrolytic medium is likely to play a significant role in the oxidation process. New analytical methodologies for the quantification of phenothiazinic derivatives in farmaceutical formulations were developed through studies focused on the definition of the optimum experimental conditions and on the effect of potential interfering species. Prometazine was determined in Fenergan (Rhodia-Farma) and in Lisador (Farmasa), whereas chlorpromazine was quantified in Amplictil (Aventis). The limits of detection (LOD) for promethazine were determined to be 1,3 10-6 mol L-1 and 3,0 10-5 mol L-1 for spectrophotometric and electrochemical measurements, while the limits of quantification (LOQ) were determined to be 1,1 10-4 mol L-1 and 2,2 10-5 mol L-1 for spectrophotometric and electrochemical measurements, respectively. For chlorpromazine, the limits of detection (LOD) were determined to be 7,6 10-5 mol L-1 and 4,1 10-5 mol L-1 for spectrophotometric and electrochemical measurements, while the limits of quantification (LOQ) were determined to be 3,3 10-4 mol L-1 and 1,6 10-4 mol L-1 for spectrophotometric and electrochemical measurements, respectively.The results obtained using both analytical curves and the standard addition methods, were consistent with the outcome of official methods and with the data supplied by the manufactures. The double response provided by the technique, amperometric and spectrophotometric, allows overcoming the interference of electroactive and colored species, hence turning this a highly selective method with an enhanced discrimination strength between the signal of the analyte and that of interfering species.

ASSUNTO(S)

análise em fluxo flow analysis spectroelectrochemistry espectroeletroquímica phenothiazinics derivatives derivados fenotiazínicos

ACESSO AO ARTIGO

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