The applicability of boron-doped diamond (BDD) as a working electrode in an amperometric cell, coupled to HPLC, was demonstrated, for determining benzodiazepines in pharmaceutical preparations. The separation of the benzodiazepines was achieved using a Waters XTerra RP18 column (250 Â 4.6 mm, 5 mm) with a mobile phase sodium phosphate (pH 3.5; 0.10 mol L . The measurements were performed in a system 871 Advanced Bioscan (Metrohm) with a BDD (8000 ppm) adapted to the thin layer mode cell. Stainless steel and platinum wire were used as reference and auxiliary electrodes, respectively. The cell was operated in pulse mode, using À 1.9 V as initial potential. The method presented linearity, repeatability and ruggedness and it represents a novel, alternative electroanalytical method for benzodiazepines determination.

Recebido em 16/9/99; aceito em 12/1/00 SPECTROPHOTOMETRIC DETERMINATION OF VITAMIN B 2 (RIBOFLAVIN) IN PHARMACEUTICAL FORMULATIONS USING FLOW INJECTION ANALYSIS. A flow injection spectrophotometric procedure exploiting merging zones is proposed for determining vitamin B 2 (riboflavin) in pharmaceutical preparations. The determination is based on the red-colored complex formation between vitamin B 2 and silver(I) which was measured at 520 nm. Vitamin B 2 was determined in four pharmaceutical preparations in the 1.0 to 50.0 mg L-1 concentration range, with a detection limit of 0.5 mg L-1. The recovery from three samples ranged from 98.0 to 104.0 %. The analytical frequency was 42 h-1 and r.s.d. were lower than 1% for solutions containing 10.0, 30.0 and 50.0 mg L-1 vitamin B 2 (n= 10). The results obtained in commercial formulations using the FIA procedure were in good agreement with those obtained by using a conventional fluorimetric procedure (r=0.9998) and also with the label values (r= 0.9997).

Dedico este trabalho aos meus pais, Milton e Elizabete e à minha irmãTaissa, por todo amor, incentivo, apoio, carinho e compreensão. vii AGRADECIMENTOSÀ minha orientadora Profa. Dra. Susanne Rath, pela oportunidade, orientação, apoio durante todos esses anos, carinho e amizade.