Development of sequential injection methodologies for the spectrophotometric direct and kinetic determination of aluminium in natural and waste waters

Raquel B R Mesquita,António O S S Rangel

doi:10.1590/s0103-50532008000600018

Abstract

Two sequential injection methodologies for the spectrophotometric determination of reactive aluminium in water samples are proposed, based on the reaction between chrome azurol S (CAS) and aluminium. The two methods involve a direct and a kinetic methodology (for its application to coloured waste waters), both accommodated within the same manifold. The working ranges obtained were: 0.040-0.500 mg Al L-1 for direct method and 0.050-0.300 mg Al L-1 for the kinetic method. The described system has high degree of automation, enabling sampling throughputs of 31 and 57 h-1 for the kinetic method and direct methods, respectively. The reagents consumption per determination is low: 46 µg of CAS, 3.75 mg of sodium acetate and 25 µg of ascorbic acid. The volume of effluent produced per determination is only around 2.8 mL in the direct method and 3.4 mL in the kinetic method.

Highlights

The generalized public interest on water quality has substantially increased the demands on water monitoring
As mentioned above the aluminium monitoring in water treatment plants is of extreme importance due to the addition of aluminium salts to the effluent water in the coagulation step
A spectrophotometric alternative for the determination of aluminium was presented enabling the screening of aluminium in water samples without any previous treatment

Summary

Introduction

The generalized public interest on water quality has substantially increased the demands on water monitoring. As mentioned above the aluminium monitoring in water treatment plants is of extreme importance due to the addition of aluminium salts (in excess) to the effluent water in the coagulation step When these waters are involved, several factors must be taken into account such as: suspended solids, turbidity and intrinsic colour, which could mean several pre treatment steps. To overcome this problem, a kinetic methodology for the same reaction was developed. Manifold for the spectrophotometric determination of aluminium in different types of water: CAS: 0.4 g L-1 chrome azurol S solution; Ac: 15% sodium acetate solution; Aa: 0.1% ascorbic acid solution; S: sample or standard; W: waste; P: peristaltic pump; SV: 8 port selection valve; HC: holding coil 300 cm; R - reaction coil (randomly knitted) 100 cm; λ: spectrophotometer at 545 nm. The analytical signal (reaction rate) corresponded to the absorbance increase per time (s)

Results and Discussion

Method

Conclusions