peak deformation during sugar and ethanol analysis with RID

[niknosnen]

I use sugar pak-I for analysis of gfructose, glucose and ethanol to monitor production of vinegar.
My mobile phase is Calcium salt of EDTA (0.025g/500 ml water) with a flow of 0.4 ml/min at 80 oC and an RI detector. I start progressivley increasing the flow and the temeperature till the working conditions each time. I have carried out numerous analysis and after a long time deformation of the peak mainly in ethanol eluting later is observed (almost 2 peaks). I regenerate the column by reversing the column and for 5-6 h passing again the solvent and after that in the past peak shape was OK. LAtely, even after the regeneration the peak problem especially in ethanol cannot be fixed in this way. Can anyone propose something?

Thanks

[tom jupille]

I suspect your column is dead. The symptoms you describe are consistent with a headspace at the top of the column. Reverse-flushing the column "fluffs" the bed of packing, but the bed gradually re-compresses and the problem returns.