Chromatography Forum

i use normal phase to determine a compound at 210 nm.I used heptane and IPA IN THE MOBILE PHASE,And i used a CN column.
My peak shows a great band of absortion at 218 nm.
in a past test done,the peak was elute verwell at 210 nm,but in that moment i used hexane and ethanol in my mobile phase and a L3 column,i.e (Si column).

any can tell me if this changes in the system do the change in the maximum of absortion of my peak?

Why happened that?

Can i do my test at 218 nm?

my employed method result invalid at 218 nm.?

Many thanks to all for your comments.
best regards
Paul.

"peak was elute verwell at 210 nm" - i don't really understand this part could you explain it

as i understand your post what you did was changing the method which included the mobile and stationary phases change and what you observed was change in maximum of absorption of your compound, right?

how did you measure that change? - any pictures or results would be useful, in what conditions did you measure it?

"my employed method result invalid at 218 nm.?" - which method? the method is valid if it is valid(ated)
If you have validated the method then you have shown that it is valid - that is the purpose of validation

First of all, if you have a "validated" method, the method must be run *exactly* the same way. Validation is a formal process widely required by pharmaceutical regulators. It demonstrates that the method does what it is supposed to do.

Now, assuming that the original method was validated: you are using a different column, a different mobile phase and a different wavelength versus the original method. So no, your results are not valid (they may or may not be correct, but they are certainly not valid).

...they may or may not be correct, but they are certainly not valid...

Well said Tom!

Than you for your useful comments
PDuque.