Graphite furnace analysis of cadmium

Hello,i have a PG-990 model AAS and I have been doing with my AAS for a long time on both FAAS and GFAAS modes but I faced a problem on the analysis of cadmium in GFAAS mode I manipulate the atomizing temperature to be 1500 degree centigrade but no difference there is no any peak observed please could you give me any suggestion.thanks!