Turbidimetric determination of sulphate employing gravity flow-based systems Original Research Article

A gravity flow-based manifold to perform turbidimetric determination of sulphate, comparing different approaches, such as sequential injection analysis (SIA), FIA with multicommutation and binary sampling (FIA-MBS), FIA with sandwich sampling (FIA-SS) and monosegmented flow analysis (MSFA) is described. Solutions of 5.0% barium chloride, 0.25 mol l−1 perchloric acid and 0.3% EDTA in 0.2 mol l−1 NaOH were used as precipitating agent, carrier fluid and cleaning solution, respectively. After optimisation, SIA, FIA-MBS and FIA-SS approaches showed linear response ranges from 40 to 200 mg l−1, while for MSFA the range was from 20 to 125 mg l−1. In the SIA system, a sampling frequency of 30 samples per hour was obtained, while a value of 40 samples per hour was obtained when FIA-MSB, FIA-SS and MSFA approaches were employed. The flow manifold was evaluated by determining sulphate in plant, bovine liver and blood serum digests. The SIA, FIA-SS, FIA-MBS and MSFA systems showed a R.S.D. of 3.2, 2.7, 2.0 and 1.0%, respectively, expressed as the relative standard deviation of the signal intensities of six measurements of a 120 mg l−1 SO42− solution. When the results were compared with those obtained by conventional FIA, no significant differences were observed for FIA-MSB, FIA-SS and MSFA at a confidence level of 95%, while for SIA the results were similar at a level of 97.5%.