DETERMINATION OF FUNCTIONAL-GROUPS ON PARTICLE SURFACES BY FLUORESCENCE AND REFLECTION SPECTROSCOPY

The application of fluorescence and reflection (absorption) measuremen ts for the determination of functional groups on surfaces has been inv estigated. As an example, amino-functionalized silica surfaces have be en studied that were labeled with the strongly colored fluorodinitrobe nzene (FDNB) and the fluorescent Lucifer Yellow VS (LY). Both with ref lection measurements and with fluorescence detection, amino groups cou ld be quantified with concentrations as low as 10 mmol/kg, which is si gnificantly lower than the detection limit attainable with conventiona l titration approaches. At concentrations higher than 250 mmol/kg for the FDNB-labeled samples and above 50 mmol/kg for the LY ones, calibra tion curves become nonlinear. From the concentration dependence of the LY fluorescence, information can be derived on the structure of the l abeled surface. Finally, it is shown that the fluorescent particles ca n also be examined individually by application of now cytometry. On th e basis of now cytometric measurements, the concentration of functiona l groups, homogeneity of functionalization, and particle size distribu tions can be obtained.