Determinação espectofométrica de hipoclorito em alvejantes e cloro em águas de abastecimento empregando sistema em fluxo por multicomutação e células convencional e de longo caminho óptico

Abstract

A multicommutation flow system for the spectrophotometric determination of hypochlorite in bleaching products using a cell with pathlength of 1 cm is proposed in this work. In this system, N,N-diethyl-p-phenylenediamine (DPD) reacts with hypochlorite and the product was monitored at 515 nm. The analytical curve for hypochlorite was linear in concentration range from 2.68x10-5 to 1.88x10-4 mol L-1 (2 to 14 mg L-1) with a detection limit of 6.84x10-6 mol L-1 (0.51 mg L-1). The sampling rate of 45 h-1 and a relative standard deviation of 1.4 % (n = 10), were obtained. The recovery of this analyte ranged from 97% to 102.5%. The results found for six bleaching products using the proposed multicommutated flow system agreed with those data obtained using a reference method (iodometric titration) at the 95 % confidence level. A multicommutation flow system for the spectrophotometric determination of chlorine in water samples using a cell with 100 cm of pathlength is also proposed in this work. In this system, dichloridrate orto-Tolidine (3,3-dimethyl bencidine) reacts with chlorine and the product was monitored at 438 nm. The analytical curve for hypochlorite was linear in the concentration range from 1.34x10-6 to 2.01x10-5 mol L-1 (0.1 to 1.5 mg L-1) with a detection limit of 9.4x10-8 mol L-1 (7.0x10-3 mg L-1). The sampling rate of 45 h-1 and a relative standard deviation of 1.0 % (n = 15), were obtained. The recovery of this analyte ranged from 96.8% to 104.6%. The results found for six water samples from São Carlos city using the proposed method agreed with those data obtained using the method used by CETESB (Kit DPD colorimetric) at the 95 % confidence level. The long pathlength optic system is composed by amorphous fluorpolymeric Teflon AF2400tube with a 100 cm of length and refraction index smaller than the water one that was used as wave guide, aiming to minimize radiation losses. Finally, flow system involving multicommutation was developed to increase analytical features, decrease the reagents consumption and residual production.