HELP! This has nothing to do with gc or hplc, but I have an ISO method that calls for the use of an "ester acid". In 30 years, I have never heard, that I can remember" this term. Can anyone tell me what this is???? thank you

I think you are referring to, if I am correct, is a half acid, half ester, or half acid ester. This is not to be confused with a half assed ester.

Seriously, I sat through a seminar in my grad school days where an outside speaker was giving a synthetic organic presentation involving half acid esters. He spoke so fast trying to get in everything he wanted to say, that every time he said "half acid ester" it sounded like, and at times did come out as "half assed ester". He had the entire faculty, some of which took themselves too seriously, rolling with laughter.

RCOO(CH2)nCOOH