1988 Volume 4 Issue 2 Pages 181-184
A sensitive and accurate method is described for the determination of phosphate with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolatoJcobalt(III) chloride (Co-5-Cl-PADAP). The ion pair of Co-5-Cl-PADAP with molybdophosphate was floated at the phase boundary between aqueous phase and butyl acetate phase when the aqueous phase was adjusted to 0.125mol dm-3sulfuric acid, 0.225mmol dm-3ammonium molybdate and 25μmol dm-3 Co-5-Cl-PADAP. After the aqueous phase was discarded, the ion pair which had been floated was dissolved by addition of methanol. The absorbance of the organic phase was measured at 560nm. The calibration curve was linear up to 0.4μg phosphorus (r=0.999). The molar absorption coefficient was 3.4×1O5dm3 mol-1 cm-1and the relative standard deviation was 1.45% for 0.4μg phosphorus (6 runs). Arsenic(V) and dodecylsulfate interfered. The proposed method was applied to the determination of phosphate in river water.
