Evaluation of DMIT [4,5-Dimercapto-1,3-Dithyol-2-Thionate] as chelating agent in a cloud point extraction procedure for [Pb.sup.2+] determination in water samples/Avaliacao do DMIT [4,5-Dimercapto-1,3-Ditiol-2-Tionato] como agente complexante em um procedimento de extracao por ponto nuvem para determinacao de [Pb.sup.2+] em amostras de agua

The present study proposes a new method for cloud point preconcentration of [Pb.sup.2+] ions based on complex formed with [4,5-dimercapto-1,3-dithyol-2-thionate] and posterior determination by flame atomic absorption spectrometry (FAAS). The preconcentration of [Pb.sup.2+] was carried at pH 5.0 under following conditions: time and temperature of batch at 15 min. and 70°C, respectively, 0.1% (v/v) Triton X-114, 0.003 mol [L.sup.-1] acetate/acetic acid buffer solution, 1.0 x [10.sup.-5] mol [L.sup.-1] DMIT and 0.5% (m/v) NaCl. Under the best analytical conditions the method provided a limit of detection of 2.85 µg [L.sup.-1] by preconcentrating 10.0 mL of sample and calibration curve ranging from 0 up to 650 µg [L.sup.-1] (r = 0.99945). The applicability of proposed method for [Pb.sup.2+] determination in natural waters without interferences was checked through addition/recovery tests. Keywords: DMIT [4,5-dimercapto-1,3-dithyol-2-thionate], cloud point, lead, FAAS. O presente estudo propoe um novo metodo para pre-concentracao por ponto nuvem de [Pb.sup.2+] baseado no complexo formado com [4,5-RELATED ARTICLE: imercapto-1,3-ditiol-2-tionato] e posterior determinacao por espectrometria de absorcao atomica em chama (FAAS). A pre-concentracao de [Pb.sup.2+] foi realizada em pH 5,0 nas seguintes condicoes: tempo e temperatura do banho de 15 min. e 70°C, respectivamente, Triton X-114 0.1% (v/v), solucao tampao acetato/acido acetico 0,003 mol [L.sup.-1], DMIT 1.0 x [10.sup.-5] mol [L.sup.-1] e NaCl 0,5% (m/v). Nas condicoes otimizadas, o metodo forneceu um limite de deteccao de 2,85 µg [L.sup.-1] preconcentrando 10,0 mL de amostra e curva de calibracao variando de 0 ate 650 µg [L.sup.-1] (r = 0,99945). A aplicabilidade do metodo proposto para determinacao de [Pb.sup.2+] em aguas naturais sem interferencias foi confirmada por meio de testes de adicao e recuperacao. Palavras-chave: DMIT [4,5-dimercapto-1,3-ditiol-2-tionato], ponto nuvem, chumbo, FAAS.