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- Posts: 3
- Joined: Wed Mar 21, 2018 11:24 am
I am running a method to analyse simultaneously two compounds and using two analogues as respective internal standards (ISs). I tried four different C18 columns (same types/brands) and found out that retention times of one analyte and 2 ISs are similar when using different columns and very stable between days. The other analyte behaves very weirdly: different retention times among different columns and with one column, it also show different retention times on different days. My mobile phase is gradient 0-100% B within 2 mins with A 0.1% formic acid in 5% ACN/water and B 0.1% formic acid in 95% ACN/water. One analyte and its IS always have retention time round 1.7 mins; the other IS elutes at 1.4 mins and the weird analyte elutes from 1.4 to 2.1 mins when it supposes to elute around 1.4 mins as its IS.
Highly appreciate if you have any suggestion to fix this retention time changing.
Thank you!