The 2-pyridinecarboxylic acid europium(III) complexes (Eu(PA)(3)) could be dissolved by acetic acid (HAC). The relationship between absorbance and concentration of Eu(PA)3 complexes in HAC was linear. The Eu(PA)(3) complexes have been in situ synthesized in the 1% EuCl3 and 3% 2-pyridinecarboxylic acid (PA) co-doped gels. The concentration of the Eu(PA)(3) complexes which had been in situ synthesized in the gel was obtained by measuring absorption spectra of the HAC solution in which the Eu(PA)(3) complexes in the gel had been extracted according to the relationship between the absorbance and the concentration of the Eu(PA)(3) complexes in HAC. The dependence of the concentration of the Eu(PA)(3) complexes which were in situ synthesized in the gel on the heat treatment time at 90 degreesC have been determined. (C) 2002 Elsevier Science B.V. All rights reserved.