Chromatography Forum

Hi,

I am having a dilemma on final calculations of an unknown sample. This is my first time to use a standard with a different salt form compared to that of the sample. My only available standard is in the "HCl" salt form whereas the drug in my sample is in the "Sulfate" salt form. I am going to use LC-MS-MS for assaying. How should I go about it?

Thanks

Just calculate on a mole basis and correct back to weight basis. The LC-MS should separate the neutral molecule from the salted part of the molecule. If you look in the void volume in negative mode, might see elution of Cl- ion.

The MS will have the same response for the compund on a mole basis since it will see the protonated form of the base whether you inject the HCl salt of the sulfate salt as long as the drug is retained on the column long enough to separate from the acid complexed with it.

For UV work, we just multiply by the appropriate formula weight ratio to convert the one salt to the other.

Sorry for not responding immediately. I was not able to get online for sometime to check the replies.

The drug that I am analyzing using LCMS is Ephedrine sulfate in the sample and my standard is Ephedrine HCl. I just want to make sure I understand clearly. So, in case my results are all expressed in the HCl based on the standard that I have, is it that I should multiply the HCl result by a factor equivalent to the ratio of MW (Eph. sulfate)/MW (Eph. HCl) where MW = molecular wt. This way the final answer would be as the sulfate form?

Thank you for your replies.

That should do it.

oops - dbl post