EXPLANATION
This test method is applicable for the determination of nitrogen in lubricating oils when present in the concentration from 0.03 to 0.10 weight %, and for the determination of nitrogen in fuel oils when present in the concentration from 0.015 to 2.0 weight %. This test method may not be applicable to certain materials containing N-O, N-N linkage, and thus in such materials may produce low nitrogen results compared to other instrumental methods, such as Test Methods ASTM D4629, ASTM D5291, or ASTM D5762.
TEST SUMMARY
The sample is digested in a mixture of concentrated sulfuric acid, potassium sulfate, mercuric oxide, and copper sulfate. After digestion, sodium sulfide is added to precipitate the mercury, and the mixture is made alkaline with caustic. Nitrogen, now in the form of ammonia, is distilled into a boric acid solution. The ammonia is titrated with standard sulfuric acid using methyl purple as an indicator.
TEST PRECISION
Where M = mean of two values.