unknow impurities

[vicentexxx]

Hi everyone,

I 'm writing to you for 2 misterious impurities that i notice on my chromatogram (0.2%). I'm sure that my product is pure because i analysed it with several purity method (HPLC) and I never noticed them. With this new method from Pharmcopeia i find these 2 impurities but I can't understand their origin. Eluent and solvent are MeOH, H2O, Na docusate and HCLO4 (pH3) and column is a bondpack C18.
These are the evidences:
- I try to inject only solvent but I can't notice impurities
- impurities are present when I have my product in the sample but if I add 50% more of my product to the same solution there is no any increasing of these impurities.
- in anther Lab (injecting the same sample) i find these impurities at 0.1%

docusate is for me the cause of these impur. but i can't inject without it because the chromatogram profile would be too different to make any comparison. the docusate in the two different labs is the same brand.

what about it?is it possible a problem in tha stationary phase?did you have any problems with docusate?

Your ideas about the cause of this impurities wuold be very useful

thank you in advance


Vicente
thank you in advance

[sassman]

It is possible that your product is not as pure as you thought it was. Under different conditions and with different columns selectivity can change so that something that coeluted with your analyte before now becomes visible. It is strange that adding more of your analyte does not result in an increase in the impurity peak. Maybe try adding double or four times to see if the impurity increases? Also possible that your analyte is reacting with the mobile phase before it reaches the detector, but I doubt that docusate is the culprit. Docusate is at a constant concentration in the mobile phase right? You didn't say what your product is.

[HW Mueller]

vicentexxx,
if these are all the observations you made it seems reasonable to assume that you cought some dirt while preparing the initial sample solution.