The following link may be useful in this regard (http://www.drug-dissolution-testing.com/?p=1270)

The single point dissolution test is only one withdrawn sample but in dissolution profile testing, multiple samples are withdrawn that may affect the % dissolved at 30 minutes in a possible significant or non significant. The drug filtered, after each withdraw, on filter paper or sample filter may affect its %. The fresh dissolution medium that will be added can be another cause for dilution of drug.

Ramy:

In a sense, you are correct that at 30 minutes, or any other time, results might be different after single sampling vs multiple sample. However, for proper comparison, these results must be corrected for sampling and volume losses. The results with correction should be similar, because the dissolution results at a particular time point must be the same (product characteristics) and if these are different then it is analytical issue not that of dissolution and/or product issue.

With regard to filtering aspect, filters should be free from the artifact as well, i.e. they should not adsorb drug with single or multiple sampling, otherwise they will introduce error in results.

May be varied, we are adding the fresh dissolution medium to maintain the sink conditions after withdrawn of 5 ml of sample for every 5 min.

I agree with Mr. Saeed , no difference in both cases if we do the correction for the amount withdrawn during the multiple points of dissolution period before the 30 min.

I also agree with Mr. Saeed . If you perform all the correctons, there'll be no difference in both cases