HPLC Infinity II - valey after peak

Hello everyone,

I have some troubles with peak evaluation in my chromatograms. We have system Agilent Infinity II with refractometric detection, we use column CarboPac PA10 (25 cm x 4 mm) and 0,1 M NaOH as a mobile phase, flow rate 1 ml/min. In this case, we have fluorodeoxyglucose and fluorodeoxymannose as analytes. During analyses, after each peak (no matter what analyte we have) a valley appears, which causes difficulties in evaluation (see attached file) – we are not able to achieve required peak resolution (Pharmacopoeia requirement). I have tried a lot of experiments to avoid these valleys, but I was not successful: reference cell of RI detector is purged well, temperature of column and detector is the same, mobile phase is freshly prepared, several columns were tested. Can someone help me to solve this problem? What is wrong? Thank you very much.

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