[tterragx]

In DIN 53240-2 Determination of Hydroxyl Value, Hydroxyl Value is define as the Hydroxyl Value from the potentiometric titration plus the Acid Value of the sample. What if the value you obtained from the potentiometric tirtation is a negative value. Will you still add it to your Acid Value to obtain the actual Hydroxyl Number?

Thank you

[Arkcon]

Not really, no.  But you've left a lot of things out of your posting, so we really can't tell.  Some thoughts:

You're going to have to explain why (and how) you got a negative value for a titration.  And also which titration you mean.  Or do you mean the the difference goes negative.  I can't follow you well.  What you're saying is you started a titration, and you were already past the endpoint, and had to back titrate to reach the starting point, or what?

Do you mean after subtracting the blank, the result goes negative?  That means your accuracy is suspect.  Did you run multiple blanks to see your precision?

Consider this topic logically:  You have to determine, in a sample, how much acid and hydroxyl impurity there is.  If this was an incredibly pure sample, you'd expect the best result to be zero impurity.  What have you found -- better than 100% purity?  Or have you found an impurity that overwhelms the assay?  Or some other error?