Limit of Free Salicylic Acid USP Test

[Sallybeetle]

Does anyone have experience with the Limit of Free Salicylic Acid USP Test?

1. I can not find the USP specified column dimensions ANYWHERE. It is a C-18 (L1) 5-µm 300 x 4.6mm column. Does anyone sell a C18 with these dimensions anymore? Would a special packed column take weeks to get?

2. Using the same column as used for last year's test (L1 10-µm 300 x 3.9mm column), my sample is at 130% label claim. But, the USP reference standard solution peak areas are similar to that seen last year.

3. Is the column internal diameter and micron size so critical that two peaks could coelute in this test? Last year's test did not show any small, closely eluting peaks that would interfere this year's sample.

As always, any answers or wisdom imparted on this subject would be greatly appreciated.

[Sallybeetle]

This test is performed for the Bismuth Subsalicylate USP raw material.

[Consumer Products Guy]

Is the column internal diameter and micron size so critical that two peaks could coelute in this test? Last year's test did not show any small, closely eluting peaks that would interfere this year's sample.

I don't think the column dimensions or micron size will have any appreciable effect here. What you're experiencing is typical outdated USP columns or techniques.

[paul duque]

hello, may be this comments can help.
my experience with free salicylic acid was with ASA tablets.
pH,was the most important factor to separate salicylic acid and ASA:pH was of 5,9

Best regards
paul

[Uwe Neue]

The column diameter has nothing to do with this. If you get such a difference, there are two possibilities: either your compound has indeed 130% of the label claim, or something is coeluting with your parent compound, because you are not using the column on which this assay was developed. It also has little to do with outdated column chemistries. In most USP methods, you separate two peaks, and this can be done even with with a column from the last century