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By Anonymous on Wednesday, June 30, 2004 - 03:02 pm:
We are currently using a GPC set-up using DMF (with 0.01 M LiCl) as eluent and PLgel columns (mixed-D). We are using a HP-1050 HPLC pump with a HP-1047A RI detector.
Our question involves the origin of a mysterious peak that is positive and then negative and shows up regardless of sample purity or sample type. It appears that it MAY be due to water, BUT it comes off at ~3000 g/mol relative to polystyrene. Has anyone ever encountered this problem???? We have a nitrogen sparge hooked up to the eluent and the peak is there even when we use fresh HPLC grade DMF (no stabilizers). there are several experienced DMF GPC users here that have NEVER seen the "water peak" at this retention time. help!!!!
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By Jan Poskrobko on Thursday, July 1, 2004 - 04:41 am:
Are You sure this peak is not from early injected samples? Is the retention time repeatable or random?
In GPC with polystyrene column and DMF is possible adsorption of more hydrophobic compounds (like esters) if some amount of water is present in DMF. Then this compounds are eluted after the total permeation time. Check water content in sparging nitrogen and in DMF
Some years ago I stooped to use PS column with DMF then I don’t remember at the moment how it looks there water injection. With more polar GPC columns and DMF water gives two peaks: positive and negative with retention times longer than total permeation time. As well by adding water, is possible to change this retention times.
We are currently using a GPC set-up using DMF (with 0.01 M LiCl) as eluent and PLgel columns (mixed-D). We are using a HP-1050 HPLC pump with a HP-1047A RI detector.
Our question involves the origin of a mysterious peak that is positive and then negative and shows up regardless of sample purity or sample type. It appears that it MAY be due to water, BUT it comes off at ~3000 g/mol relative to polystyrene. Has anyone ever encountered this problem???? We have a nitrogen sparge hooked up to the eluent and the peak is there even when we use fresh HPLC grade DMF (no stabilizers). there are several experienced DMF GPC users here that have NEVER seen the "water peak" at this retention time. help!!!!
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By Jan Poskrobko on Thursday, July 1, 2004 - 04:41 am:
Are You sure this peak is not from early injected samples? Is the retention time repeatable or random?
In GPC with polystyrene column and DMF is possible adsorption of more hydrophobic compounds (like esters) if some amount of water is present in DMF. Then this compounds are eluted after the total permeation time. Check water content in sparging nitrogen and in DMF
Some years ago I stooped to use PS column with DMF then I don’t remember at the moment how it looks there water injection. With more polar GPC columns and DMF water gives two peaks: positive and negative with retention times longer than total permeation time. As well by adding water, is possible to change this retention times.
