An accurate and sensitive analysis of trace and ultratrace metallic impurities in plastics by NAA

Neutron activation analysis (NAA) has been studied to improve the accuracy and sensitivity of the analysis of trace and ultratrace metallic impurities in plastic materials. There are two main problems in the analysis of plast ics by NAA. First the contamination during sample preparation, especially s ample crushing procedure is very serious for ultratrace analysis. Another p roblem is the destruction of the sample capsule due to the pressure build-u p by the gases formed during neutron irradiation. A simple preparation tech nique of the sample crushing method using liquid nitrogen and reducing the capsule pressure by a pin hole was developed to solve the above problems. T wo different irradiation and seven cooling conditions were also investigate d to optimize the experimental conditions. A SRM from NIST (1632b coal) has been used to investigate the accuracy of the analysis. More than thirty el ements could be analyzed in the range of sub-ppb to percent. Samples analyz ed in this work were polyethylene and polypropylene which were made by diff erent manufacturing procedure, and pigments. Two kinds of plastic products used for food and drug containers were also analyzed. It was found that NAA could be a powerful technique for the analysis of metallic impurities in p lastics even though their concentrations were at ultratrace levels.