Apparatus and method for analyzing fluid streams for their content of elemental and ionic mercury even in the presence of other contaminants, for example, elemental or available chlorine. The sample is automatically measured and treated with aqueous stannous chloride reagent. The resulting elemental mercury is transferred to a photometric detector and the results are indicated and/or recorded automatically, accurately and rapidly. The apparatus and method are especially useful in the control of mercury contamination in the environment and also for monitoring chemical process streams.

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