I am working on IC-Pak Ion exclusion column for ethanol determination. My mobile phase is 0.5 uM H2SO4. When I equllibrate the system, a peak always appears at 9 minute. I have washed my column with water, dil HCL, acetonytrile and methanol for several times but again when i equilibrate to make base line, again a peak appears at 9 minute. Can someone please explain either the problem lies in my column or mobile phase or what else?
Thanks

P.S: according to reported data ethanol peak also appear at 8 or 9 minute... but this peak appears every time without sample load.