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This method is for determining sodium in petroleum distillate fractions, No. 2 fuel oil and lighter, over a concentration range of 0.03 ppm to about 1 wt-%. Sodium in samples may result, for example, from entrainment of aqueous droplets from a caustic washing operation or may be present as an oil-soluble salt. Analyses can be made for: (a) total sodium, which includes suspended alkali plus oil-soluble salts, and (b) oil-soluble sodium salts.
The sodium content of the heavier distillates, whole crude, or residual oils should be determined by means of a wet-ashing technique, such as described in UOP Method 391.