DETECTION AND SORPTION STUDY OF DIOXOURANIUM(VI) IONS ON N-(2-MERCAPTOPROPIONYL)GLYCINE-MODIFIED SILVER COLLOID BY SURFACE-ENHANCED RAMAN-SCATTERING

An aqueous silver colloid activated at 514 nm with 10(-3) M N-(2-merca ptopropionyl)glycine (MPG) involves surface-active sites for the compl exation of uranyl ions and displays the v(5) UO22+ SER spectrum at 840 cm(-1), allowing uranyl detection at concentrations as low as 5 x 10( -9) M. This level of detection competes successfully with spectrophoto metric and fluorimetric determination. A quantitative study of the SER spectra as a function of total uranyl concentrations in the colloid, ranging between 5 x 10(-9) and 1 x 10(-5) M, shows that half of the so rption sites are occupied by uranyl for a total uranyl concentration o f about 10(-7) M; from this value, a 100-fold concentration increase i nduces only a twofold enhancement of the uranyl band at 840 cm(-1), al though no appreciable change of the colloid appears. As a result of an analysis of the uranyl colmplexation either in solution or simultaneo usly with several sorbed MPG molecules, the surface site concentration for uranyl sorption in the colloid used is estimated to be close to 1 0(-8) M. This value corresponds to about one complexation site per pri mary particle of silver, perhaps at contacts between aggregated partic les. At such sites, MPG molecules bonded to the metal surfaces through S-Ag bonds still involve amide and carboxylate groups free to coordin ate an uranyl ion. The mean enhancement of the Raman cross-section of uranyl at the surface complexation sites reaches 3 x 10(5) with respec t to uranyl nitrate aqueous solution. (C) John Wiley & Sons, Ltd.