Avaliação e síntese de corantes fenotiazínicos para determinação espectrofotométrica de sulfeto e sulfito empregando sistemas de análise em fluxo.




In this work seven aromatic amines O e N-substituted were evaluated at optimized reaction conditions for symmetrics phenothiazinic dyes. DMPD, DEPD, PPD, PAP e PAA were the start reagent, where the yield for phenothiazinic dyes varying from 10% to 43% for different oxidizing (Fe3+ or ClO-), acids (H2SO4 or HBF4) and precipitant agent (ClO4 - or BF4 -). The lowest variations for reaction yields at different reaction conditions were obtained with DMPD. The potential of synthesized dyes were compared for spectrophotometric determination of sulfide by flow injection analysis (FIA). Initially the absorbance obtained with the flow system for phenothiazinium dyes produced by five different amines were evaluated in the same conditions. Since three of evaluated amines (DMD, DEPD and PPD) had shown better reaction kinetics, they were selected for subsequent experiments. The parameters related to the concentration of amine, oxidizing agent (Fe3+) and H2SO4 were evaluated. A central composite design was employed for the optimization of reaction conditions by using response surface strategy. In the evaluated concentrations conditions for three investigated parameters, only DMPD showed optimal condition with ruggedness for small variation of the optimized parameters. Even through the DEPD did not attained optimal condition at the experimental ranges it presented the highest molar absortivity (LD, 18,34 mg L-1). At the best studied conditions for sulfide determination PPD and DMPD the detection limits (3s) were calculated for 60.1 mg L-1 and 71.46 mg L-1, respectively. Notwithstanding a flow system procedure for indirect sulfite determination was proposed. This species was converted to SO2 and reduced to H2S in strong acidic medium and in the presence of Zn, in a conversion rate of 10.31%. In this sense an integrator operation device were developed and coupled in the flow system for sample preparation (HSO3 - Æ SO2) following the conversion to H2S, gas permeation through PTFE membrane and for the reaction with DMPD and Fe3+ in order to produce methylene blue. The PTFE membrane was selective to H2S compared with SO2, at different conditions. In order to sampling the H2S generated with sulfite conversion, an electronic circuit was developed to control a set of solenoid valves and to interrupt the acceptor solution into the integrator device. The system was optimized and NaOH solution acceptor lead to better results in comparison with a solution of DMPD and Fe3+. A carrier solution with 15% (v/v) in ethanol had minimized the matrix effect of wine samples. Interference of H2S at concentration higher than 0,5 mg L-1 and higher than 10 mg L-1 in the absence and presence of zinc acetate, respectively, were observed for the proposed proceedure. The procedure in flow system showed distinct analytical ranges for free and total sulfite with detection limits (3s) of 0.35 and 1.2 mg L-1, respectively, and it was employed for sulfite determination in juices and wines samples. The results obtained by proposed method were compared with reference method with agreement for 95% confidence level.


unidade integradora de operações síntese de corantes fenotiazínicos quimica analitica sulfite determination sulfide determination aromatics amines flow injection analysis determinação de sulfito aminas aromáticas integrator operation device phenothiazinic dyes synthesis sistema de análise em fluxo determinação de sulfeto

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