By Anonymous on Monday, January 5, 2004 - 06:33 am:
I routinely use 0.1%TFA (in HPLC water) and MeCN at 70/30. I then use 100% MeCN as a wash and overnight storage.
Occasionally I want to use HPLC water and MeCN at 80/20 and 190nm with the same column. I run 100% MeCN again prior to this mobile phase. The equilibration (flat baseline) takes about 90 to 120mins.
Is this solely due to flushing residual TFA from the column?
I am using a Bonus-RP amide phase.
Any ideas would be great
Dave
By Chris Pohl on Monday, January 5, 2004 - 10:10 am:
Dave,
Our tests indicate that Bonus-RP contains a significant number of weak anion exchange sites. These sites are probably responsible for the slow release of trifluoroacetic acid. My suggestion would be to try adding an intermediate rinse solution solution containing a UV transparent anion such as sulfate to speed up the elution of the trifluoroacetic acid (make sure you use an HPLC grade salt for this purpose). 10-15 minutes of rinse should be sufficient for this purpose. Then you can switch to your 80/20 eluent.
By Anonymous on Wednesday, January 7, 2004 - 03:04 am:
Thanks Chris.
I have tried the same procedure using a BDS C18 phase and the baseline settles in 20-30mins compared to 90-120mins.
I need to re-evaluate the BDS C18 for my samples.
Saved me some time!!
Dave
By Uwe Neue on Wednesday, January 7, 2004 - 06:09 pm:
Some of the packings with embedded polar groups are free from this problem. Among them are the XTerra RP and SymmetryShield packings from Waters and the Discovery RP Amide C16 from Supelco. You still have the advantage of the good peak shape and the unique selectivity of packings with an embedded polar group.
By Anonymous on Thursday, January 8, 2004 - 02:14 am:
I did use Discovery RP Amide C16 but they didn't offer a 3.5um particle so I started using RP-Bonus - which gave slightly different selectivity.
Dave