Abstract:In order to determine sulphur trioxid, first, the sample should be treated with dilute hydrochloric acid. Under acidic conditions, sulphur trioxid in the gypsum samples occurred in sulfate in testing solution as sulphate, then filtrated acid insoluble substances. After processing, the testing solution can be determined directly on the inductively coupled plasma atomic emission spectrometer. The detection limit of the determination method is 0.01%, and national standard materials are GBW03109, GBW03109a, GBW03110 and GBW03111a. It is showed that the relative error of standard sample is 0.26%~0.69%, allowed limit of relative error is 1.45% which can meet the quality requirements.