The present work proposes the application of the 4-Hidroxy-3-(2-hydroxynaphtylazo)-benzenesulphonic acid (C.I. 15670), Alizarine Violet N (AVN), as a reagent for direct aluminium determination using molecular absorption spectrophotometry in the presence of tensoatives. Al(III) cation reacts with AVN in pH 9.4, forming a red complex, stable for at least 24 hours, with absorption minimum at 607nm and, against a reagent blank, (epsiloncomplex - epsilonreagent) = -2.71x10(4) L.mol-1.cm-1. The reaction occurs in the presence of a Triton-X100 and CTAB tensoatives mixture, in the presence of EDTA. Al(III) determination is possible in the linear range of 50 up to 400ng.mL-1, with a detection limit of 41 ng.mL-1.

No presente trabalho apresenta-se um método seletivo e sensível para rápida determinação de urânio usando o 2-(2-Tiazolilazo)-p-Cresol (TAC). O TAC reage com o urânio(VI) em pH 6,5 formando um complexo estável por pelo menos 3 h. Brometo de N-cetil-N,N,N-trimetil amônio (CTAB) e triton X-100 foram usados para aumento da sensibilidade e solubilidade do sistema respectivamente. O método permite a determinação de urânio na faixa de 0,30 a 12,0 mig mL-1 com absortividade molar estimada em 1,31 x 10(4) L mol-1 cm-1 e limite de detecção de 26 ng mL-1 em 588 nm. O uso do ácido 1,2-ciclohexilenodinitrilo tetraacético (CyDTA) como agente mascarante aumenta a seletividade do reagente para a determinação de urânio. O método proposto foi aplicado para determinação de urânio em água drenada de mina onde a precisão (R.S.D. < 2%) e exatidão obtidas foram satisfatórias.

A sensitive and selective spectrophotometric method is proposed for the rapid determination of uranium using 2-(2- Thiazolylazo)-p-Cresol (TAC). The reaction between TAC and uranium (VI) is instantaneous at pH 6.5 and the absorbance remains stable for over 3 h. N-cetyl-N,N,N-trimethylamonium bromide (CTAB) and triton X-100 are used for increasing the sensitivity and solubility of the system respectively. The method allows the determination of uranium in the range from 0.30 to 12.0 mug mL-1 with a molar absorptivity of 1.31 x 10(4) L mol-1 cm-1 and features a detection limit of 26 ng mL-1 at 588 nm. The selectivity of the reagent was improved by the use of (1,2-cyclohexylenedinitrilo) tetraacetic acid (CyDTA) as masking agent. The proposed method has been successfully applied to the determination of uranium in mine drainage waters. The precision (R.S.D. < 2%) and the accuracy obtained were satisfactory.

Cr(III) slowly forms a violet complex with EDTA at pH 2.5-5.0 under normal conditions. The complex formation can be accelerated by irradiating the reacting mixture with microwave energy. The complex Cr(III)-EDTA is completely formed within 3 minutes of microwave irradiation and followed by a simple and rapid method for spectrophotometric determination of chromium. The method may be successfully applied to determination of chromium in catalyst.