3RD-ORDER DERIVATIVE SPECTROPHOTOMETRIC DETERMINATION OF PHOSPHATE ASTERNARY COMPLEX WITH MOLYBDATE AND RHODAMINE 6G

This paper describes a third-order derivative spectrophotometric proce dure for the determination of traces of phosphate, based on the format ion of a ternary ion-association complex by reaction of phosphate with rhodamine 6G in the presence of molybdate. The pink complex is readil y formed in 0.08-0.16 M H2SO4 medium and remained stable for 2 h. The influence of various instrumental parameters and reaction conditions f or maximum colour development are discussed. The few interfering ions can be masked by the addition of appropriate reagents. The procedure i s simple, rapid and reliable and allows the determination of 1.5 mug l -1 of phosphate. The relative standard deviation for the determination of 0.08 mg l-1 of phosphate was 1.1%. The method is applicable to the determination of phosphate in river water, sea water, drinking water, milk powder and standard reference materials.