The application status of current detection method for trace chloride ion at home and aboard was summarized.On this basis

this paper improved the spectrophotometric method and proposed an online measurement method for trace chloride ion in water vapor system of power stations

which modifies the formula of chromogenic agent and adds the concentration system and waste liquid treatment device.The chromogenic agent consists of a variety of additives and is a water soluble medicament with low toxicity.This online method can detect chloride ions with concentration range from 0μg/L to 1 000μg/L.Application of this method on chloride ions detection for a 300 MW

600 MW and 1 000 MW unit shows that

the minimum detection limit of this trace chloride ion online measuring method can reach 0.2μg/L

the relative deviation of the measurement results is small and has good repeatability and accuracy

indicating this method can be applied in the monitoring of chlorine ion concentration in the water vapor system of power plants.