Can someone explain me about the definition of true boiling point (TBP). There are certain ASTM standards by which TBP of petroleum fractions are determined. ASTM D2892 method corresponds to TBP distillation of crude oil while ASTM D-86 does not determine True boiling point. I would like to know more about these methods for determining crude assay.

If it is possible for you, search for the book "Elements of petroleum processing" by D.S. Jones.
It's excellent engineering literature, and it can provide full set of information you are looking for.

Thanks a lot. I'll look for that reference book.