Determination of phosphate in natural water employing a monosegmented flow system with simultaneous multiple injection

A monosegmented flow system was employed for the determination of low contents of phosphate in natural water. In this approach, sample and reagents are simultaneously injected to a PTFE reaction coil where the homogenization of the mixture occurs while the monosegment is pumped forwards the photometric detector. The proposed system was evaluated by determining phosphate ion, based on the reaction of association between molybdophosphate and malachite green. It was evaluated individually the best concentration of the reagent solution in relation to blank signal (absorbance of the blank) and the sensitivity of the method. A factorial design was proposed to explain the contribution of each component on the formation of the ion association complex, evaluating the individual contributions as well as the synergistic and antagonistic effects. With the established conditions, phosphorous is determined in the concentration range of 5.0–75 μg P PO43− l−1 (r=0.9992), with a detection limit of 0.70 μg P PO43− l−1 and a relative standard deviation of 2% (20 μg P PO43− l−1, n=8). The proposed method has a sampling frequency of 72 h−1.