Abstract: Analyzing sample blending adequately strong nitric acid, high chlorin acid and hydrofluoric acid by self-controlling technology for cleaning microwave digestion under the pressure of optical fiber. Rapidly decomposing by adopting increasing ladder pressure in 0.5MPa 2min, 1.0MPa 2min, 1.5MPa 1min under the fixed deferent power 650W of microware with a simple and convenient, quick, accurate result also reducing analytic liquid polluting. Correctitude across examination was adopted to choose the best digestion system. The detection limit was 0.20μg/cm3, RSD 1.90%, CV 98.70%～100.70%.The method has been used for the determination of Pb in foods with a satisfactory result.

Key words: self-controling pressure, microwave digestion, dithizone spectrophotometric, foods, Pb