My SRM for ASTM D4739 is NIST 1848 Lubricating oil additive. It's certified value for TBN is 44~55.2. But my results show negative values.
Other samples results are minus as well.
I use Mettler Toledo Autotitrator.

Why do I get negative values on TBN?

Is there any other SRM available for ASTM D4739 not D2896? Please recommend one.

Thanks,
Viv

This message has been edited. Last edited by: Viv,

What is the unit of the TBN?

TBN is measured in mg KOH/g. However, I'd like to know if it is the only SRM for TBN. Is there any others? I'm also looking to check my titrator performance.

You don't say if this problems is just for this range of testing.
We had a simmilar situation when we started to use a new titrator (replacement) as you know the equipment reads millivolts. What happened, whe inverted the inputs in the rear part of titrator. May be this help.