Chemical Treatment before Irradiation:
In some cases chemical separations are required before irradiation as a special measure because the concentration of analyte in the sample is too small or if speciation studies are to be carried out. This is often referred to as chemical neutron activation analysis (CNAA). These may be of following types;
Preconcentration NAA: It is especially useful in case of water samples because of low levels of analyte elements present (at µg or ng or even pg/cm3). For this purpose, water is passed through an ion exchange resins or some other adsorbent where the analyte elements are retained. In other cases, measured volume of water can be drying ashed whereby the sample size is reduced and analyte elements are concentrated.
Chemical Neutron Activation Analysis (CNAA): It was developed for determining trace amounts of analyte elements such as As and Hg in a variety of matrices including water, sedimentary rock, plant, animal organs etc. In this case, a chemical procedure is followed whereby trace elements are separated before irradiation and thus sensitivity is enhanced.