Determination of phosphorus in river water, sewer water and domestic waste water by inductively coupled plasma-optical emission spectrometry

An inductively coupled plasma-optical emission spectrometry (ICP-OES) forthe determination of phosphorus in water samples was studied. The extent of the interferences of the spectral lines from argon, NO emission and stray light for the analytical line was investigated in detail and the best experimental conditions were established. No spectral line interferences from matrix elements were observed for the second order line of P I 213.62 nm, while the spectral lines from argon at 427.22 nm and NO emission overlapped with the analytical line, giving rise to the positive interferences. The spectral intensity of the former increased at higher temperature part of the plasma, that is, at the off-axis part of the plasma and lower observation height above load coil, and the latter increased at the center and fringe of the plasma. These spectral line interferences were able to be minimized by optimizing the source parameters as follows: RF power (1.4 kW); argon gas flowrate: plasma gas (1.2 1/min), coolant gas (10.3 1/min) and carrier gas (1.0 1/min); and observation height (12 mm above load coil). The interference from stray light was also observed for the analytical line. The spectral back ground level increased rectilinearly with increasing the concentration of magnesium: the presence of 1000 ppm of magnesium gave an interference equivalent to 2 ppm of phosphorus. The interference of magnesium was able to be easily eliminated by a preliminary cation-exchange procedure. With the optimal conditions, a preactical detection limit of 0.13 ppm was achieved and the method established was applied to the determination of phosphorus in water samples in comparison with colorimetric method in good agre ement.