Buffer selection

[Nay Win Kyaw]

Hell everyone
Again please! May I kindly request your kind suggestions.We have low experience in HPLC.
For our project, we use HPLC analysis of USP and the mobile phase is 37% of aqueous phase (0.1 mMEDTA in a mixture of phosphate buffer pH 6 and water, 3:1) and 67% of organic phase (acetonitrile and methanol, 2:27).
Sample preparation is dissolving the drug in diluent (40g/L EDTA in water/adjust pH to pH 7).
Now, we would like to continue in-vitro drug release assay with Franz diffusion cell. We found that the drug is more soluble in acetate buffer and we have plan to use acetate buffer as receptor medium.But the point we worry is the difference in ionic strength between acetate buffer of receptor medium and phosphate buffer of mobile phase. And also, we need to dilute the sample (collected from receptor medium of acetate buffer) with diluent EDTA.
Could you please suggest me?
1. Should I change the mobile phase of phosphate buffer into acetate buffer? or
2. Could I use the same mobile phase?

[tom jupille]

First of all, if you are running the USP method in a regulated environment (GLP or cGMP), then you must run it "as-is" or verify that a modified method is equivalent.

As far as buffers go, you didn't specify the ioic strength of the acetate buffer but as long as it is not too different from the phosphate buffer (say, a factor of 2), then it should not matter.
If your injection volume is small enough, even bigger disparities can be accomodated.

If this were my problem, I would try using the existing (phosphate) mobile phase with the new (acetate) diluent and see what happens. We can speculate all day, but the experiment will give the answer.

[Nay Win Kyaw]

Thanks so much Tom for your kind suggestion.I use sodium acetate buffer pH 5 and 50mM.It's still ok for HPLC but I worry for long time.If I inject many times,can it affect the column?May I apologise you for my delay response.I just see your reply.Thanks so much.

[tom jupille]

I would not expect any problems.

[Nay Win Kyaw]

Thanks so much Tom