Detection on paper, III

The NAA measurements on the paper samples were made at the Breazeale Nuclear Reactor Facility at the Pennsylvania State University with a TRIGA Mark III reactor at a flux of about 1013 n/cm2-sec. Samples were irradiated from 2 to 20 min and counted for 2000 sec, after a 90 min decay time for Ba and a 60 hr decay for Sb, Analyses were performed instrumentally, without radiochemical separation, using a 35cm3 coaxial Ge-Li detector and a 4096-channel pulse height analyzer. With these procedures, detection limits for Ba and Sb were 0.02ug and 0.001 ug, respectively. These sensitivities are comparable to those obtained by GA s radiochemical separation procedure, and are made possible by the use of the higher neutron output from the more powerful reactor and in combination with the higher resolution solid state detector... 

Due to the modifications of the electronic cloud induced by complexation, the quantum yield and the excitation spectrum are also modified. As the direct determination of the absolute quantum yield is very difficult to achieve, one usually finds in the literature quantum yield values determined by comparison to well-known standards, such as quinine sulfate. For example, some values can be found in Georges (1993) or in Klink et al. (2000) for some europium complexes but may be found also in many other papers on lanthanide luminescence. Studies on the correlations between the photophysical properties of a given type of europium complexes and the energy levels can be found in Latva et al. (1997), Klink et al. (2000). A correlation has been found between the excitation properties and the stoichiometry of various Eu(III) complexes (Choppin and Wang, 1997). Note that the changes in the excitation maximum induced by complexation usually amount to a few tenths of nanometers, which requires high resolution for detection. In the case of Eu(III), a correlation has been found between the frequency... 

Immunoassay bv Visual Comparison. During the course of this study, 421 Immunoassay analyses were made by visual comparison as described previously in this paper. Immunoassay analyses on these same samples were also made with the aid of a spectrophotometer in addition, 180 of the samples were analyzed by GC/MS. A comparison of the visual analysis with spectrophotometrlc Immunoassay results and GS-MS results is given in Table III. The results Indicate a visual detection limit for Immunoassay of about 0.5 ug/L. For the 173 samples in which the visual analysis results were negative, 98 percent of the spectrophotometrlc analyses were less than 0.5 ug/L. Also, for 45 of these samples that were analyzed by GC/MS, 98 percent contained less than 0.5 ug/L of atrazlne. 

---