Chromatography Forum

Hi, I have been doing optimizing a new HPLC method on a new "aqueous" column and ran into some older issues that I had on a spherisORB ODS2 C18 column. There is a persistent blob that always comes off the column.

At around 4 min past the solvent front we begin to see the weird blob. Here are some things I have tried to fix the problem.

HPLC- columbic cell detector

- replace the mobile and flush column
- clean and replace rheodyne parts
- replace sample loop
- try different percentages of MeOH (does seem to move blob slightly)
- injecting pure MeOH makes the blob really big

When I just do the trigger I don't see the blob, however, if I inject mobile phase into the loop I see the blob. If I inject water I see the blob or if I inject the sample I also see the blob.

It might be just me, but I have some troubles understanding your terminology. What is a columbic cell detector? Does 'doing the trigger' means a run without injection?

Which mobile phases are you using? Is this a gradient method? What column are you using?

I can sort of imagine what a blob looks like but a chromatogram would help!

Have you tried the same method and injections with a different column? Both a different identical column and perhaps a non-identical column?

we are using a ESA model 5011 analytical cell and ESA model 5021 conditioning cell for the detection. I am using a rheodyne valve for injections when I say trigger only that means I am only flipping the valve to start the run with no injection. This is a manual injection system.