ASTM D7622 Standard Test Method for Total Mercury in Crude Oil Using Combustion and Direct Cold Vapor Atomic Absorption Method with Zeeman Background Correction
4. Summary of Test Method
4.1 Controlled heating following thermal decomposition of the analysis sample in air is used to liberate mercury. The sample is placed into the sample boat, which is inserted in the first chamber of the atomizer, where the sample is heated at controlled temperature at 300 °C to 500 °C (depending on the selected operation mode). The mercury compounds are evaporated and partially dissociated forming elemental mercury vapor. Mercury and all decomposition products are carried to the second chamber of the atomizer heated to about 700 °C to 750 °C (mercury reduction takes place on the surface of heating NiCr coil, thus no catalyst is required). Mercury compounds are totally dissociated, and the organic matrix of the sample is burnt out. Continuously flowing air carries mercury and other combustion products through absorbance analytical cell heated up to 750 °C positioned in the light path of double-wave cold vapor Zeeman atomic absorption spectrophotometer. The mercury resonance line 253.65 nm is split to several components, one of those falling within the mercury absorbance line (analytical line) profile and another one lying outside (reference line). Difference between the intensities of these compounds is proportional to number of mercury atoms in the analytical cell. Absorbance peak area or peak height is a function of the mercury concentration.
NOTE 1 - Mercury and mercury salts can be volatized at low temperatures. Precautions against inadvertent mercury loss should be taken when using this test method.
5. Significance and Use
5.1 The emission of mercury during crude oil refining is an environmental concern. The emission of mercury may also contaminate refined products and form amalgams with metals, such as aluminum.
5.2 When representative test portions are analyzed according to this procedure, the total mercury is representative of concentrations in the sample.
