Determination of ng ml-1 levels of phosphorus in waters by diisobutyl ketone extraction and inductively coupled plasma atomic emission spectrometry

Reduced molybdoantimonylphosphoric acid is extracted into diisobutyl ketone (DIBK) and phosphorus in the extract determined by i.c.p. emission spectrometry at the P I 214.91-nm line. The Mo II 213.61 nm line interfered with the P I 213.62-nm line. The method is applied to 0.2–200 μg of phosphorus in 500 ml of river or sea water. Arsenic(III), Si, Ge, Fe(III) and most anions do not interfere, but As(V) >10 × P) causes positive errors. The detection limit is 0.37 ng P ml^-1, and the relative standard deviation for 5 μg of phosphorus is 2.1%.