Abstract: Phosphate is involved in a number of important biomineralization processes such as bone formation as well as pathological processes such as the genesis of renal stones. Consequently, its determination in biological fluids is important. The determination of free phosphate ion in human urine and serum is very important, since they have diagnostic value in some clinical cases. Here we report a simple and sensitive method to determine phosphate in urine and serum. This new ensemble was prepared by adding ytterbium chloride and pyrocatechol violet in a 2∶1 molar ratio in aqueous solution of 10 mmol/L HEPES buffer at pH=7.0. With the addition of urine or serum sample, in UV-Vis absorption spectra the maximum absorption peak gradually shifts from 623 nm to 444 nm and the ensemble results in a change of color from blue to yellow. The ensemble exhibits an excellent selectivity for phosphate over other constituents of urine and serum. Mean urine and serum phosphate concentrations found in healthy individual are 23.25 and 1.14 mmol/L respectively. The detection results are basically consistent with those of normal excretion of phosphate.

Key words: Phosphate, Urine, Serum, Pyrocatechol violet-PV, YbCl₃, UV-Vis spectra