Pre-concentration by electrostacking and by cloud point for determination of metallic ions in environmental and biological samples / Pre-concentração por electrostacking e por ponto nuvem para determinação de arsenio e cadmio em amostras ambientais e biologicas

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The propose of this work is to study two pre-concentration systems for the determination of metallic ions by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption speetrometry (ETAAS). First, the use of the bi-directional electrostacking system (BDES) for the pre-concentration and speciation of As(V) and total As in water samples employing ETAAS teehnique was related. In the refered system, the As (V) is pre-concentrated applying the potential difference, such as capillary electrophoresis (CE). The parameters investigated for As pre-concentration are: sampling zone (150 mL aliquot collected sequentially), sample tube dimension (12.4 e 4.1 cm in length), voltage (500, 750 and 1000 V), time employed in the voltage application (5, 10, 15,20 and 40 min), pH of the sample (4.0; 7.0; 8.0 and 12.0), nature of buffer solution (Tris/HCI, glycine/NaOH and H3BO3/NaOH) and buffer concentration ( 0.05 - 0.2 mol L ). In such case, the better conditions for the pre-concentration of As(V) are: voltage of 750 V applied during 20 min and using the buffer H3BO3/NaOH in the concentration of 0,05 mol L. In such conditions is possible to obtain a pre-concentration factor (PF) as 5 times. The pre-concentration of As (III) applying the same system optimize for the As (V) was also studied. Notwithstanding, this system condition was not efficient for the pre-concentration of As (III). In this case, the As (III) is oxidized to As(V) using KMnO4 and H2SO4. The oxidation efficiency ranges from 75.0 to 85.0 % and the PF is also 5 folds. Another pre-concentration system investigated is the extraction/pre-concentration based on the cloud point. Two complexing agents (1-(2-pyridilaze) 2-naphtol (PAN) and O,O - diethyl ditiophosphate ammonia (DDTP) was investigated. Triton X-114 is employing as surfactant. A NaCI 1 % (m/v) solution is used to induce the cloud point formation without heating. Others effects are studied (the complexation time, Cd standard volume and Triton X-114 volume and volume of ethanol added to dilute the micelle). The obtained results changing the complexation time show that the values of PF remain constant for both systems tested. Additionaly the DDTP (from 0.01 to 0.2 mol L) and PAN (from 2.7 x 10 to 2.7 X 10 mol L) concentration is optimized. Employing PAN at 1.0 x 10 mol L concentration a maximum PF (6.5) is obtained, and for DDTP at 0.05 mol L the PF is 6.3. A decrease on PF of Cd is observed for these two systems (Cd-PAN e Cd-DDTP) when increased the surfactant concentration, being that using with Triton X-114 at 0.04 % (m/v) a better analytical result was obtained. The volumes between 400 to 1800 mL of ethanol/HNO3 were evaluated. The results show that ethanol/HNO3 volume of 400 mL correspond to the best pre-concentration factor for Cd, and a PF of 16 and 19 times was observed when Cd-PAN and Cd-DDTP was used respectively. After optimized the methodology, it is apply for pre-concentration of Cd in cigarette sample, lake water, mineral water and physiology solution with quantification by flame atomic absorption spectrometry. Good recoveries were obtained for all analyzed samples.

ASSUNTO(S)

cloud point preconcentration electrostacking pre-concentração ponto nuvem electrostacking

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