measuring and mixing acetonitrile and water.. - wat is the accurate and reproducible way to do this? (Apr/22/2010 )

hi all..
i need to make a mix of acetonitrile and water.. with TFA for use in RP-HPLC.
i observe many shifts in retention time when i use different preparations of the mobile phase.

i wished to know what is the right way to measure and mix, temperature etc to make such a mobile phase consistently.
any ideas?

thanks!

I work with HPLC-DAD my retention times vary over the course of a day (+- 30sec) with the same mobile phase used throughout. Assuming you mix you mobile phase the same way ever time you are probably doing the best that can be acheived.

I tend to work with the problem of changing retention times, not try to fix the problem. You could try running some compounds that don't degrade easily and show a distinct peak within the parametres your RF-HPLC runs. I use caffeine and beta-carotene. From here you have a marker for the variation and adjustment of your rention times. But I guess this idea depends on your project... good luck!

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thanks for the responses..

mdfenko, thanks for the reply but im unable to open the last webpage.. cud u please send me the contents..
thanks much!

sorry, i was mistaken, the link would not answer your question.

this hplc troubleshooting guide from waters should answer your question (chapter 30 should handle most of the question), keep in mind that whichever way you choose to prepare your mobile phase, be consistent: