HPLC - quantification of tea catechins

[murugesh]

I am using Epigallocatechin (EGC) along with other 3 major tea catechins viz.,EGCG, ECG and EC as standards in HPLC based quantification of these catechins in tea samples. But the EGC concentration in samples based on the callibration graph is unusually high(mere impossible), this experiment was repeated number of times to rule out experimental error(weight of standard, dilution, sample preparation). The slope of the calibration graph is 375, the area under the curve expressed in mV. I am using isocratic elution, mobile phase is water:methanol:acetic acid(73:23:1). Coloumn is oyster BDS premium C18 (300mm X 4.6 mm), coloumn temperature: 313K. What could be the possible error.

Waiting for the kind response from experts
Murugesh

[tom jupille]

Given that you have already checked for "pilot error", the next most likely explanation is co-eluting interferences.

[murugesh]

Given that you have already checked for "pilot error", the next most likely explanation is co-eluting interferences.

Thank you for your suggestion, i ll check the co-eluting interferences.

[juddc]

The first co-eluting species I might suspect would be caffeine. Where does that elute?

[murugesh]

The first co-eluting species I might suspect would be caffeine. Where does that elute?

The retention time of EGC is 6.6 min but for caffeine it is 13.5 min.

Murugesh