Determination of ultratrace iron in KH2PO4 by derivative adsorption chronopotentiometry

A sensitive derivative adsorption chronopotentiometric method for the determination of ultratrace Fe(III) in KH2PO4 has been studied based on the formation of the Fe(III) complex with 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). The influence of KH2PO4 on the signal of the reduction of the complex Fe(III) with 5-Br-PADAP was discussed. Fe(III) was separated from the solution containing KH2PO4 by using the coprecipitation of Fe2S3 with PbS prior to electrochemical detection. The method was used for determination of ultratrace Fe(III) in KH2PO4 crystals and its saturated liquor with satisfactory results.