DETERMINATION OF INORGANIC-PHOSPHATE BY FLOW-INJECTION WITH FLUORESCENCE QUENCHING

An FI method using fluorescence quenching for the determination of pho sphate ions is proposed, The method is based on the ability of phospha tes to inhibit the formation of a strongly fluorescent complex of scan dium ions with ydroxy-1-naphthaldehyde-p-methoxy-benzoylhydrazone (HNA MBH) in weakly acidic (pH 4) water-ethanol (50% v/v) mixtures, The opt imal chemical conditions for fluorescence quenching of the HNAMBH-Sc c omplex by phosphates were studied, and a simple FI manifold was develo ped, 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 constituent s are suppressed, The measurement throughput was 120 h(-1), The ranges of application (as phosphorus) are 3.0-15 mu g l(-1) and 15-150 mu g l(-1), The detection limit of the method is 3.0 mu g l(-1) (3.0 mg l(- 1) for serum, high concentration range) and 0.8 mu g 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 mu g l(-1) of phosphorus were 5.7; 5.2 and 1.8%, and fo r 30.0, 60.0 and 120 mu g 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%),