Foam remover

[Mattias]

Sorry to bother you again with this benzalkonium chloride (BAC) determination, but this molecule seems to be more tricky that I first anticipated.

When I prepare standard solutions, the BAC forms a foam. This foam is highly enriched with BAC making the bulk solution too weak. Does anyone now a good way to avoid the formation of foam?

I have tested to add some EtOH in the end of the preparation - and this removes the foam. However, I need to mix the solution afterwards and the foam is formed again. I am limited to about 20% organic to avoid peak distortion in the LC.

[krickos]

Hi

Adding a magnetic stir bar and stirr very gently?

Sonication?

[chemgeek]

What kind of agitation are you using? I have used a stir bar at moderate speed with good success. Also a vortexer at a low setting worked well.

The only other option I can see is to be patient and allow the foam to settle and agitate gently.

[Consumer Products Guy]

We constantly make aqueous solutions of cleaning products, anionic surfactants, and cationic surfactants such as BAC. We mix by stirring, with the foam just about at the volumetric flask neck. We pull up the stirring bar higher than the mark with an external magnet, add a few ml alcohol to break the foam, add water to the mark, lower the stirring bar gently using the external magnet, then stir. Believe me, most cleaning products and anionic surfactants foam way more than BAC.

[Mattias]

Thanks!

I have just turned the volumetric flasks upside down a couple of times. I am not too fond of "fishing" for magnetic stirrers - this method is going to a QC lab and who knows what "fishing gear" they may use.

I will try ultrasonic and see what happens. I found that in 50% EtOH the BAC will not form any foam no matter how I shake the flask. To my surprise I could inject 50 µl of this solution and still have identical chromatography. This could be the way to go.

By the way, the foam consists mostly of the C14 analog. This is probably why I loose only the C14 analog in some samples. Strange but true!

[Dan]

Two compounds that I have heard used in these situations are: simethicone and n-octanol.

Simethicone is the active ingerdient in those OTC anti-gas products. I don't recall the concentration that is used, but I remember it doesn't take a lot of the simethicone, just a little works.

I heard that the use of n-octanol is mentioned in one of the the USP dissolution Chapters, <711> or <1092>. It takes only a few (2-3) drops of n-octanol per 100 - 200 mL of solution.

I have never tried either compound. I have only tried to minimized shaking and stirring to avoid the problem.

Regards,
Dan

[Vlad Orlovsky]

on several occasions I used THF to suppress foaming.

[Mattias]

Thanks a lot!

Vlad> Is there any risk of injecting 50% EtOH on the Primesep D? I remember that Primesep is not compatible with MeOH.

[Vlad Orlovsky]

Mattias,

You are okay with alcohols and Primesep D which yo use for benzalkonium. You need to avoid alcohol with cation-exchange mixed-mode, which can be esterified/modified.