Related to same Retention Time

[kspansheria]

Dear all,

If I analyzed my product (e.g. Levonorgestrel & Ethinyl Estradiol Tablet) on dual wavelength say 210nm & 254nm for two different molecules. Oneknown impurity integrated on one RT at one wavelength (say 210nm and at same RT but different wavelength (say 254nm) one impurity comes what should I mark that impurity????


Regards
Kamlesh

[unmgvar]

why do you think it is a different compound?
many compounds have absorbance spectrums that can stretch from 200 to 280nm
do you have a PDA or MS to confirm that these are different compounds eluting at the same RT?
can you do a UV spectrum of that known impurity?

after you have shown that these are indeed different compounds eluting at the exact or approximate RT then depending on their UV spectras you can decide what to do

for example if each compound does not share any absorbing range with the other, then their value are correct and you can simply look at this at 2 dinstinct chromatograms
if either one of them absorbs at 210 or 254 then you must separate them in your chromatography.

[Alex Buske]

If something absorbs at 254nm it is most likely that it also absorbs at 210 nm. If it is a known impurity you have to take the higher amount (if 210 nm gives 0.1% and 254nm gives 0.25% then you have to use 0.25%) unless you have done a accuracy validation and maybe established response factors. If it is a a unknown impurity you have to calculate it with respect to lower concentrated API (according to ICH impurity guideline).