Chromatography Forum

Would it be necessary to stir mobile phase on a stir plate while doing runs? Advantageous, even in the presence of IPn reagents...? Many a thank you in advance.

Philip

No

It should never be a requirement to stir mobile phases as everything should be in solution before you start. If buffer components and the like start to precipitate there is an inherant robustness problem that should have been dealt with during method deveopment.

I hope that helps

John

Try running insulin some time, you will find yourself with a heated stir plate sitting atop your LC.

the IPn reagents are in the mobile phase?
can you show your method? they are numerous easy methods for the separation of insulin out there.
do you have some special requirements because of the nature of your samples?

The impurity assays for insulin are anything but easy. And not I can not provide any detail as these methods are company confidential.

This is from the USP, so you get the idea:

Related compounds—
Solvent— Dissolve 28.4 g of anhydrous sodium sulfate in 1000 mL of water. Pipet 2.7 mL of phosphoric acid into this solution, adjust, if necessary, with ethanolamine to a pH of 2.3, and mix.

When the lab temperature cooled down overnight (to save money), things sometimes liked to drop out solution.

From what has been mentioned here recently, one could conclude that the USP should be thrown out of the window.
A mobile phase which might or might not have ethanolamine in it, precipitates when the temp changes a bit, made by dissolving Na2SO4 (why anhydrous when hydrates are much better defined??) in 1000mL (what´s the final volume?), and pipetting H3PO4 (what %?). Neat.
AA, did the stirring keep your stuff in solution or the heat produced by the stirrer? Just curious: Any idea how much the savings were due to lowering the heating as compared to the extra expenses due to digging out of the ice the next morning?

From what has been mentioned here recently, one could conclude that the USP should be thrown out of the window.

If you're bored, and want casual entertainment, read the USP Expert Committee's responses to improvement suggestions, example available below,
http://www.usp.org/pdf/EN/USPNF/USP30-N ... entary.pdf

For example,
Cefepime Hydrochloride
Comment Summary #2: For the Related compounds test the commenter questioned the validity of adjusting the pH of the Mobile phase component solutions after the addition of organic.
Response: Comment not incorporated. The Committee believes that the current Mobile phase preparation is valid. The commenter did not supply data to support a revision.

Ibuprofen monograph
Comment Summary #1: Commenter claimed that the title “impurity Câ€

You wont get any argument from me that many of the methods in the USP are very poor and could really use an upgrade. But, as the last poster points out, the USP is an organization that is somewhat resistant to change.

i might be thrown sticks and stones for saying this but on the other hand USP gives you the tools to show your own validated method.
we generally don't do it because it cost less at the R&D stage and when we give our drug for approval it is faster cheaper and more importantly less questions, since it is a USP crappy method that we say we use.
but in the long run the QCs are stuck with a very poor method that causes big delays and increase expense costs daramatically.
i think i will call it the easy, lazy generic appraoch

like jtreacy said, it is an inherant robustness problem.
the correct aproach is too revalidate. in the long run it will cost you a lot less in time, money and especially nerves