Determination of alkali-labile phosphoprotein phosphorus from fish plasma using the Tb³⁺-tiron complex as a fluorescence probe

A sensitive method based on the fluorescence quenching effect of the Tb³⁺-Tiron complex is proposed for the determination of alkali-labile phosphoprotein phosphorus (ALP) released from fish plasma. The detection limit was 5.4 ng/ml (S/N=2), and the relative standard deviation of the quenching effect (6 replicates) was 4.6%. The results obtained by the proposed method were in good agreement with those obtained by the colorimetric assay. The advantages of the present method are its relatively simple detection procedure, the lack of toxic organic solvents, and high sensitivity.