Determination of orthophosphates using a macro segmented flow analyzer (MSFA) based on colorimetric detection

Fabrication of a macro segmented flow analysis (MSFA) system based on reconfiguration of the manifold by adjustment of the sample/reagent ratio, has been found to produce a sensitive method for orthophosphate analysis based on colorimetric detection at 880 nm. Optimization of sample tube length, reaction temperature and molybdate concentration in the carrier solutions has been carried out. The larger sample tube internal diameter led to the combined advantages of better sensitivities, wider working range and higher sample throughput over most existing methods. Using the optimized conditions of 50.0 cm sample tube length (1.6 mm i.d.), 37.0 °C reaction temperature and 0.0113 M molybdate concentration in the carrier solution, the calibration model for orthophosphate standard solutions was found to be linear (y = 0.04895x + 0.003561; correlation coefficient, r2=0.9970) over the working range 0.01–2.00 mg l−1 orthophosphate. The volume of the sample injected was 1.396 ml at a flow rate of 6.0 ml min−1. The sample throughput of this MSFA method was 40 samples per an hour, with a detection limit of 4.0 μg l−1, and %R.S.D.’s below 5%. The MSFA method was successfully applied to analysis of water and wastewater samples.