Chromatography Forum

Hello all,

I am using a waters RI detector to measure sugar levels in dairy product samples and since my last calibaration I have been consistently detecting a mystery peak between the lactose and glucose peaks. I am using reversed phase with 0.02N H2SO4 mobile phase.

I am going crazy trying to find out what that peak could be! Does anyone have any idea?

First off, 20 mN H2SO4 is an unusual mobile phase. What kind of column are you using?

Next, does the mystery peak show up in blanks and samples or only in samples?

One of the disadvantages of RI is that it's universal (that's also one of its advantages!), which means that you could be seeing something as simple as a system peak.

Under those conditions on an ion exchange column the most common thing that would come out between lactose and glucose would be citric acid.