ELSEVIER Analytica Chimica Acta 331 (1996) 271-280 l4luALmc.A zyxwvutsrq CHIMICA zyxwvutsrqpon ACTA Determination of sulphate in natural waters and industrial effluents by sequential injection analysis J.F. van Staden *, R.E. Taljaard zyxwvutsrqponmlkjihgfedcbaZYXWV Department of Chemistry, University of Pretoria, Pretoria 0002, South Africa Received 6 December 1995; revised 26 February 1996; accepted 12 March 1996 Abstract A sequential injection analysis system for the determination of sulphate in natural waters and industrial effluents has been developed. The method is based on the turbidimetric determination of sulphate using barium chloride as reagent and measuring the absorbance of the formed suspension spectrophotometrically at 540nm. The proposed system is fully computerised and is able to monitor sulphate in samples at a frequency of 26 samples per hour with a relative standard deviation of better than 3.9%. The calibration graph is linear between 10 and 200mgl-‘. Keywc7rds: Sequential injection; Sulphate; Spectrophotometry; Turbidimetry; Industrial effluents; Natural waters 1. Introduction The quality of water, especially drinking water is very important to human life. In a country like South Africa with its periodic periods of drought, water is a relatively scarce commodity. Furthermore, the recent drought in our country resulted in a dramatic decrease in our natural water resources. This inevitably results in an increase in the concentration of substances in the water system. The limited available water resources, therefore, automatically lead to rigid environmental requirements. In this circumstances the quality of available water becomes a factor to be seriously considered within water supplies. Pollution of the fresh water sources is, therefore, a main concern as it determines the quality of water. There is * Corresponding author. Fax: +27 12 432863. 0003-2670/96/1$15.00 0 1996 Elsevier Science B.V. All rights reserved PIfSOOO3-2670(96)00 139-O thus an increasing need for process analysers to monitor natural water streams and industrial efflu- ents. The sulphate ion is one of the components that needs monitoring. Several approaches have already been described for the determination of sulphate ions. The existing manual methods, for example the standard gravimetric method [l] and the titrimetric methods [2,3], including potentiometric methods with ion-selective electrodes, which usually involve precipitation titrations with lead(H) solution and a lead-selective electrode [3-S], are all cumbersome, tedious and time-consuming. Accordingiy, a number of spectrophotometric methods for determining sulphate have been developed. The three methods that appear to be used almost universally are the barium chloroanilate method [9,10], the methylthy- mol blue method [l l] and the barium sulphate