Constant Carryover

[lauries]

I am having issues with constant carryover on an Agilent 1100. The peak is at the same retention time as my peak of interest.

I see this with two method with two different columns. I am assuming it is the same stuff (pluronic f68). One method: 90%water10%thf to 100% thf on DVB column. If I run 50%water50%thf to 100% thf I see no peak. I believe this is because the mobile phase is strong enough to not allow it to build on the head of the column. My other method is 100%meoh to 100%thf, also on DVB column. I tried a brand new DVB column and still see stuff! (different pore size, so it looks a little different) Using ELSD detection, peak is at about 90%thf, 10% meoh.

I do believe the contamination is before the column since my retention times are always the same.

I do not believe it is in the injector because: I took out the needle and needle seat and sonicated them in meoh. While I did this, I hooked the pump directly up to the column, so no part of the injector was in the system. I continued to do runs and still got my peak.

I ran a special cleaning mix of organic solvents in all mobile channels up to where the column is (kept the column off) for 20 min, 5 mL/min. Cleaned my mobile bottles (with the fresh hplc grade solvent straight from a virgin bottle) and refilled them. Then ran my solvents through the lines. changed the purge valve frit. Still seeing the dang thing! I don't know where else it could be!

Any thoughts?

[tom jupille]

Run the "three blank gradients" test as described in the "mini-tutorial" on gradient artifact peaks: viewtopic.php?f=31&t=19085 (you can scroll forward to about 4.5 minutes). From what you have already done, I suspect that it is contamination coming from your weak solvent. If you have a two-pump system, you can use the guard cartridge trick, or with a one-pump system you can try filtering your A mobile phase through an SPE filter disk (both are described near the end of the video).

[carls]

Did you change the filters in the solvent reserviors?

[lauries]

So. I have two methods. 1= 100% methanol to 100% thf and I saw the carryover at about 6 min on a 8 min run. 2=90% water 10% thf to 100% thf. I thought it was in my thf since it was common between the two methods. The methods had different columns but same instrument.

On method 2 I was able to cure it my changing my thf to acn. Another reason I thought it was my thf.

For method 1, I put it on a new instrument. All mobile bottles were completely unique, so if it was a contaminant that had gotten into the mobile on the first instrument, it should not be in the second. I still see the peak in every single run when I do meoh to thf. HOWEVER... if I do ACN to THF... I don't see the contamination! So the second experiment leads me to believe the contamination is in the meoh. This then leads me to believe the meoh is contaminated from the manufacturer (it is supposed to hplc grade, but I'm getting a 150 count height peak!). So right now I'm distilling it. But I'm still wondering if it's in the THF, and maybe only manifests itself with the meoh present.

Any thoughts? I am also observing lines in my thf mobile bottle as the solvent level goes down. I am currently doing LCMS on the meoh and thf to try to identify it. I'm pretty sure it's peg, but it would be good to know which one it is in for sure. I definitely do not want to distill the THF due to safety issues. Perhaps there is an spe filter for this? The THF is unstabilized, hplc grade.

[Klaus I.]

Any thoughts? I am also observing lines in my thf mobile bottle as the solvent level goes down. I am currently doing LCMS on the meoh and thf to try to identify it. I'm pretty sure it's peg, but it would be good to know which one it is in for sure. I definitely do not want to distill the THF due to safety issues. Perhaps there is an spe filter for this? The THF is unstabilized, hplc grade.

You are also observing the described blank-peaks when you use a freshly opened THF-bottle (HPLC-grade without stabilizer) and using also new bottles of (undistilled and also hplc-grade) other solvents and doing no injection?