Aerosol can sampling

[Consumer Products Guy]

I'd like to pose a question for others: how does one best sample an aerosol can, for example, if one wants to assay for an active in the entire product (concentrate plus propellant is the sample). If we're interested in identity of propellant, we can always puncture the can using an adapter and withdraw a sample in a gas syringe, or put a non-lubricated condom over the can, spray some out, and draw out some propellant in a gas syringe. If we freeze the can, open and let propellant escape, we have to back-calculate based upon the percent of propellant v. concentrate, and the concentrate holds a bit of the propellant for a while, and may lose other volatiles while the propellant comes off. Therein lies the issue, thanks for any ideas.

[Mark Tracy]

Just an idea. After freezing the can and releasing the propellant, transfer the liquid to a flask. Refreeze the liquid, and apply vacuum. You will need to do some experiments to get the temperature, pressure and time such that the propellant is removed, but the volatiles of interest are kept.

[GOM]

Hi,

I use this can piercer from Alltech. http://alltechweb.com/productinfo/techn ... /u8013.pdf
together with a Precision Sampling Corp Pressure lok 25ul syringe.

I sometimes sample directly from the nozzle using an adaptor fitted with a disposable syringe. I dispense into a butyl septum sealed headspace vial about 50% full with acetone or ethyl acetate. You can't do this with all cans because there are three types of dispenser.

1. No dip tube - so turn the can upside down and dispense
2. Dip tube - keep can upright
3. Dip tube with a vapour phase tap i.e. a hole near the top so that the liquid and headspace are dispensed at the same time.

Sometimes you have to cut a can open to find out which type is present.
So the liquid can be sampled representatively through the nozzle with 1 and 2. one of the problems is that every time you sample what is left behind changes as the contents re-equilibrate.

Hope that helps - coincidentally I have one coming in next week to analyse.

Regards,

Ralph

[Consumer Products Guy]

I need to have a representative sample of the entire contents for my sample weight, that's how the active is calculated. That's the issue.

[GOM]

Hi,

What is the active? I presume that this is an LC application?

Regards,

Ralph

[Consumer Products Guy]

The active is aluminum chlorohydrate, aerosol antiperspirant. There are no other sources of chloride than the active, so a potentiometric silver nitrate titration of the chloride ratioed v. the chloride content of the aluminum chlorohydrate itself delivers the amount in the product. My pointy-haired boss doesn't want to trust the amount listed on the can. It pays the bills....

[ym3142]

assuming the propellant does not interfere the active titration:
1) find the accurate total amount of an aliquot of the product;
2) find a solvent which will complete dissolve the product or at least the acitve;
3) find the amount of the active by titration;
4) cal the percentage of active in the product.
Or may be I do not understand your problem yet.

[HW Mueller]

Assuming that the chlorohydrate is not volatile (otherwise it wouldn´t do much antiperspiration), maybe you can weigh the can, take everything out, evaporate the propellant (freeze-thaw?), weigh the leftovers, analyze them for chlorohydrate content.....? (A bit similar to what Mark suggested)

[Peter Apps]

How about:

Weigh the whole can plus contents.

Chilll it to below the boiling point of the propellant at 1 atmosphere, puncture the can then slowly warm it to get a smooth evaporation of the propellant.

Weigh the can plus non-propellant ingredients. This gives you the mass of propellant. To be sure that all the propellant is gone you can evaporate to constant weight.

Cut around the can, remove a portion of the contents and weigh the portion. Wash out the remnants and weigh the can. This gives the weight of the non-propellant, and the weight of the total contents.

Assay the weighed portion for active.

Mass fraction of active in portion times weight of non-propellant gives mass of active in can.

Mass of active in can divided by mass of contents gives mass fraction of active in contents.


Peter

[GOM]

Hi,

We use the principle outlined by Peter for this with just a slight modification - we use the can piercer that I mentioned earlier, place the preweighed can on its side at room temperature, pierce the septum with a hypodermic needle and allow the propellant to escape. Then cut open the can and transfer the contents. You can use a C18 Sep-pak to remove silicones. The ACH is water soluble and is analysed by an LC method.

Regards,

Ralph

[Consumer Products Guy]

Ralph - you assay the aluminum chlorohydrate by an HPLC procedure??? Can you post details of that procedure, and why you use HPLC? Also, I want to re-inforce that one should ALWAYS for safety use non-sparking tools like berylium when opening a can containing flammable propellants.

[GOM]

Hi,

Yes, but it is an in-house method based on size exclusion developed for patent work when we were part of a large consumer product company and I really am sorry but this is one where I cannot give away the details.

Regards,

Ralph