[aclark91]

Hi guys This is my first post here, might not be the last! I'm having to run some dilutions on standards so I can run them on an HPLC system and discover retinoid concentrations in feeds.
I have received my standard, retinol palmitate, which came in 100mg neat. I'm going to dissolve the oil in 2ml of ethanol or hexane so I get a conc of 50mg/ml. I've been told by colleagues today that a good thing to do is prepare another stock solution of 1mg/ml which you can use to make up working solutions while you have a nice, almost full stock of 50mg/ml in the -20.
Just to clarify, because dilutions were never my strong point, if i want to dilute 50mg/ml to 1mg/ml would I take 0.1 microlitres of stock and dissolve in 5ml of ethanol?
I then need to prepare another solution of 1ng/per microlitre. I worked with someone last year and I saw him take 0.1 microlitres of stock and dissolve in 10ml of ethanol to get to this concentration, and for the life of me I cannot figure out how he got that or if I even was watching the right thing
If anyone can show me how I can get 1ng/per microlitre from a stock of 1mg/ml I would be extremely grateful. Literally any advice/help you guys can give will be very much appreciated
Hope to hear from you, looking forward to your replies

[Borek]

Dilution is based on the idea that amount of substance doesn't change - how much you put into the solution will be there after dilution.

In other words, it is just a mass conservation, no magic.