Determination of inorganic phosphate by flow injection with fluorescence quenching

Abstract

An FI method using fluorescence quenching for the determination of phosphate ions is proposed. The method is based on the ability of phosphates to inhibit the formation of a strongly fluorescent complex of scandium ions with 2-hydroxy-1-naphthaldehyde-p-methoxy-benzoylhydrazone (HNAMBH) in weakly acidic (pH 4) water–ethanol (50% v/v) mixtures. The optimal chemical conditions for fluorescence quenching of the HNAMBH–Sc complex by phosphates were studied, and a simple FI manifold was developed. The method has been applied to the determination of phosphate in blood serum. The sensitivity of the method allows a 1:1000 dilution of the serum samples, so that interferences from other serum constituents are suppressed. The measurement throughput was 120 h^–1. The ranges of application (as phosphorus) are 3.0–15 µg l^–1 and 15–150 µg l^–1. The detection limit of the method is 3.0 µg l^–1(3.0 mg l^–1 for serum, high concentration range) and 0.8 µg l^–1(0.8 mg l^–1 for serum, low concentration range). Within-run s_r values for 6.0, 9.0 and 15.0 µg l^–1 of phosphorus were 5.7, 5.2 and 1.8%, and for 30.0, 60.0 and 120 µg l^–1 of phosphorus were 2.6, 2.5 and 1.8%, respectively. Analytical recoveries from serum samples range from 95.5 to 103.9%(mean 99.1%).