Chromatography Forum

Hello,

Just a quick question about your experiences with mobile phase lifetimes. How long do you normally use a mobile phase prep (ie: buffers, pure water, organics, mixes, modified, etc)? Are these expiry dates based upon experimentation or just common sense?

I curious about practices. If there any articles that you know, directions would be appreciated.

thanks,

Ravi

Mobile phase expiration is generally dictated in the method or by lab SOP. Generally, fresh is best. Having said that, I personally try to remake mobile phase after one week as a general rule. I have seen chromatography deterioration after as little as one day, but have also had reproducable data after mobile phase has been on the bench for 2 months. I am always aware of mobile phase prepartaion dates. Mobile phase preparation needs to be evaluated on a case by case basis.

i think fresh is best , beware of bacterial/fungal growth in aqueous systems. Sterile techniques may have to be considered for prolonged storage. But case by case basis dependent on SOP. I would always prepare mobile phases with minor volatile additives on a daily basis unless validated process shows storage is not a problem.

What about 'stability' during analysis. For example, when we use ethanol anhydrous as one of mobile phase component, how do we keep it still anhydrous when we run the analysis?

What is all this fuzz about mobile phase stability? Your standards will show when it is not useable anymore. You also can device methods with which to check them, admittedly, not always easy with UV. Also, if you see microbe colonies in your bottle it´s high time to part with it... all common sense. Guess, the regulations take common sense out of it.

Which regulations? How does one determine what is a proper lifetime in order to get an accurate SOP?

How long does MilliQ (Analytical Grade) water normally last before you throw it out (1, 3, 7, 14, longer) ? How about modified mobile phases (i.e. TFA)? Organic mobile phases? Buffered (do you take pH into account)? How about mixed?

The reason for this is that there is a little debate amongst my collegues and I was soliciting some general practices from members of this board. I'm interested in the rationale for the lifetimes.

thanks for your input.

Ravi

When writing a method or providing input on a method, I try to avoid specifying how long mobile phases can be stored. Then I can use them as long as my system-suitability, check standards etc., pass the method criteria. Or for as long as common sense dictates, as HW Mueller said. If I have 500 mL of ACN/water mixture left that is 8 days old, and all method checks are fine, then why should I dump it in the waste bucket? Hmm?

GLP requires that the mobile phases be labeled with an expiration date, but does not specify what the expiration date must be. I label them with preparation and expiration dates, with the expiration being the longest I would ever keep the stuff in accordance with common sense, although I do try to be consistent with this.

Edit: forgot to include my expiration dates.

Aqueous/organic>10% or organic/organic mixtures: 6 months.

Aqueous or aqueous/organic<10%: 1 month. (I have stored them longer than this without observing anything floating in the bottle; I don't use phosphate containing mobile phases).

Direct question:
How do we keep ethanol absolute still anhydrous during analysis when it is used for mobile phase? How to prevent moist absorption by this solvent that can change the composition of mobile phase?

What else is in the mobile phase besides EtOH?

The mobile phase is a mixture of methanol and ethanol anhydrous (13:7). It is USP method for ubidecarenone.

We used to attach a trap filled with anhydrous CaSO4, partially with a blue indicator version (Fluka), to anything which had to be kept in communication with the atmosphere, yet had to be kept dry.
Actually, in your case I would give it a try to keep going until I notice a chromatographic change, could be a long time unless you willfully "moisturize" your solvent.

Friends,

Iagree with all the comments of previous postings. Everybody is right about everything (or mostly so). I would like just to add my 10cents worth of experience here.

Most mobile phases are sort of immune to bacterial growth if they contain a large ( i.e. 20%) content of an organic modifier (ACN, MeOH). However, those are are mostly aqueous and close to pH 7 will develop this problem quite rapidly. This seems to be most agravated when phosphates are also present.

Many instruments employ some sort of He degassing system, and that means that the phases are always blanketed by a very inert atmosphere, obviously this enhances the stability of the phase as long as it is not sparging all the time. Prolonged sparging will tend to decrease the % of the volatile components. Therefore it is a good practice to sparge for 5-10 min when the phase is freshly prepared and then maintain only a very small flow of He of close it all and maintain the He blanket. I have heard of substantial loses of organic solvents when the sparging is 20 min of so.

Some laboratories employ "phase concentrates" that are kept in refrigeration. These are diluted at the moment of use and just in the amount needed for a particular determination.

In summary, phases are always better use fresh, and even though it is possible to keep them for some time, and the basic question is why do it?

Good Luck,

Benjamin