migration time shifting in chiral CE assay

[wangqg]

Hi, All,
I am runing a chiral CE assay. The condition is roughly as follow:
50umx56cm capillary, 5% sulfatd CD with 10% acetontrile in 25mM phosphate TEA buffer, pH 2.5, -15kV, and the peaks come out around 20min. The migration time of all peak are roughly decreased about 0.2 min after every injection (5 min rinse with buffer between injections). If no acetontrile in buffer, there is no shift. Is this due to acetontrile evaporazition or something else? The solvent evaporazition seems fairly quick to me if it is the reason.

Thanks a lot.

[Fiz]

Hi, All,
I am runing a chiral CE assay. The condition is roughly as follow:
50umx56cm capillary, 5% sulfatd CD with 10% acetontrile in 25mM phosphate TEA buffer, pH 2.5, -15kV, and the peaks come out around 20min. The migration time of all peak are roughly decreased about 0.2 min after every injection (5 min rinse with buffer between injections). If no acetontrile in buffer, there is no shift. Is this due to acetontrile evaporazition or something else? The solvent evaporazition seems fairly quick to me if it is the reason.

Thanks a lot.

Maybe try first after every run the following: Rinse 1 min. with 0.1M NaOH (to reactivate and clean the inner surface) then rinse 1 min. with water and finally rinse at least 3 min. with buffer. I would think that this solves your problem.

[Rob]

Try also putting some extra run buffer vials on the system and running each injection with a pair of fresh buffer vials to see if that removes the MT drift between runs. I am wondering if you get a pH/electrolyte change during the run which is somehow accentuated when the buffer contains ACN.

[wangqg]

Bob and Fiz,
Thanks for the suggestions. I used 0.1N NaOH rinse, and it gave the same result, ~ 0. 2 min decrease every injection. Using new buffer vials helps, but there is not very convenient in routine analysis.