I am working on a formulation having three active ingradients. I want to set method for dissolution test for this multicomponent formula. My problem is one of the early eluting peak ampong three components (RT about 3 min)is failing for peak purity test in acid stage only. Peak purity is passing in Buffer pH 6.8 and Mobile phase containing buffer and acetonitrile adjusted to pH 6.8.
My dilutions are
1 tab ---> 900 ml with 0.1N HCl
aliquote ---> diluted with mobile phase.or
1 tab ---> 900 ml with Buffer pH 6.8
aliquote ---> diluted with mobile phase.
My question is
1) What may be the reason.
2) What is possible remedy.

I think you shold work out a system where all three peaks will be retained well. That`s all.
Constantine

This question was posted twice and received two responses. none of the responders seemed to understand the requirements for dissolution sample analysis. When analyzing dissolution samples by HPLC, seeing individual impurity or degradant is not necessary, but getting the main components separated in a short time is critical (< 10 min, preferably isocratic conditions). Having to make over 100 injections a day is nothing unusual in a dissolution lab. If you developed an HPLC method with more than 15 min run time, the QC lab analysts may curse you when they are running this method.

The problem could be limited buffer capacity of the mobile phase. Have you check sample apparent pH after diluting with m.p. (for acid stage only)? What’s the pKa of your first component?

Dear Anonymous,

I Understood your problem. Your formulation is a delayed release formulation, am I right, hence there should not be any drug release in the Acid stage, and it should start releasing as soon as you transfer it to buffer stage. How can you find a peak in acid stage at that particular retention time since there is no release. Think that there is a partial release also, the interference could be due to the placebo peaks etc., check the pH of the solution which you are injecting, it may be acidic when compared to the Buffer stage sample. This could be one of the reason where there is a chance that pKa of the molecule is altered and some peak which is eluting close to the first peak may be merging with it. chekc for any closely eluting peak in the buffer stage sample. Try to decrease the solvent concentration in mobile phase and push off the peak much later may be upto 5 minutes and check. Since most of the buffers also interfere may be roughly upto about 5 minutes depending upon the type of buffer matrix which you are using.

I will agree with the answer that jt gave, there is no need to look for peak purity in dissolution testing. The only thing that you should look is a fast reliable separation for the quantification of your analytes.
A faster way is by using UV derivatives for the three analytes if the 1st and 2nd derivative spectra's don't have ovelapping regions (zero point crossing)