Dear Kasun,

please find attached a paper (Abdel-Hadi, M. A., A SIMPLE APPARATUS FOR BIOGAS QUALITY DETERMINATION) reporting the use of KOH solutions at a concentration of 40%. The authors cite other works in which the concentration of KOH were:10%, 33% and 40% (APHA et al., 1992; Hamilton and Stephen, 1964; Okeke and Ezekoye, 2006).

Thanks a lot. I've used 9N KOH and it really worked well. Yeah higher concentration is better.