Chromatography Forum

Hi everyone,

I am a novice HPLC user. At the moment I am trying to analyze 5-HIAA in brain tissue. I am using two positive controls (25 ng/ml and 10 ng/ml), the problem is that the HPLC is telling me that the concentrations for 5-HIAA are approx. 6ng/ml in the 25ng/ml and 3 ng/ml in the 10 ng/ml.
I was told to consider changing the electric potential of the channel that is measuring it. It is currently at 130 mV. Does anybody have suggestions what electric potential is best when measuring 5-HIAA

agfahey,

We run our 5-HAIAAs at 350mv. The setting may depend on your detector cell but it looks to me like you aren't supplying enough voltage to induce the REDOX changes that are actually measured. Are you using a coulometric system or amperometric? Either way, ramp up those mVs and watch the strip chart. You know you've used to many mV if the signal is too quick (you burn off all those electrons too fast).