I am using a smaller diameter column than my previous one keeping all other factors such as stationary phase, solvent, solvent gradient constant. (Obviously, flow rate will be less in smaller column). I would like to know will changing the diameter affect the retention time of my target?
The key idea is that when you change column diameter, you keep the superficial linear velocity the same. For example if I have an analyte which elutes on a 10 cm x 4.6 mm i.d column at 7 minutes at 1 mL/min. Now we change the diameter to 3 mm, we have to use a flow rate of 0.425 mL/min to keep the retention time the same. Now we wish reduce the diameter further, say 2.1 mm i.d., now you should use 0.21 mL/min so that your analyte elutes at 7 minutes.
Search the keyword: superficial linear velocity, HPLC