[Beaker]

   There are many products which make use of activated charcoal, such as air filters and 3M Tarni-Shield Strips.  How can I determine whether the activated charcoal still has any potency, and if possible, what that level of potency is?  (And by that, I don't mean insofar as scientific units, but rather whether the activated charcoal is completely fresh, half "strength", mostly useless, etc...)

   Surely there must be a way to test for this without requiring extensive equipment?

[Alpha-Omega]

I think you are speaking of materials used in the household.  Tarni-Shield Strips are activated charcoal strips that people usually place in jewelry boxes to prevent tranishing of silver, nickel, copper, bronze, brass, tin
and gold. Place in box or bag with jewelry. They are advertised as "Lasts up to six months, depending on exposure to air  (one year in a sealed environment)."  Activated charcoal air filters are used to adsorb irritants and undesirable materials from the ambient atmosphere.

It would not be unreasonable to see the effectiveness to be dramatically decreased, depending on the amount of material that is being adsorbed on the surface of these strips and filters. 

Upon exposure to the air (ambient environment) activated charcoal will adsorb stuff.   Activated charcoal exerts its effects by adsorption.  Adsorption is a process in which atoms and molecules move from a bulk phase (such as a solid, liquid, or gas) onto a solid or liquid surface.

The charcoal is "activated" because it is produced to have a very fine particle size. This increases the overall surface area and adsorptive capacity of the charcoal. It is produced by adding acid and steam to carbonaceous materials such as wood, coal, rye starch, or coconut shells.

Therefore, once exposed to the atmosphere it will adsob and its "potency" effectiveness will be decreased dramatically.

Theoretically, the fact that those strips are kept in a box would imply that the environment is sealed.  That is not really accurate and correct.  Jewelry boxes are opened and closed.  the amount of undesirable junk in the atmosphere can change depending on ambient conditions.

I would imagine that the lifetime of these strips and filters is quite variable depending on ambient conditions.

Activated charcoal is a fine black odorless and tasteless powder made from wood or other materials that have been exposed to very high temperatures in an airless environment. It is then treated, or activated, to increase its ability to adsorb various substances by reheating with oxidizing gas or other chemicals to break it into a very fine powder. Activated charcoal is pure carbon specially processed to make it highly adsorbent of particles and gases.

In the lab, activated charcoal is kept in a sealed vessel so nothing in the amient environment can affect the material. These conditions preserve the effectiveness of the material.  Of course it has an expiration date that has to be acknowledged.

Activated charcoal is also ingested to eliminate toxins from the body.  It ia an antoxin for poisoning.  It is used to induce vomiting if accidental overdosing or a suicide attemted is suspected. It is also used for deodorizing and  gastro-intestinal distress associated with influenza. There are differnt forms:  powders, capsules, pills, etc...With regard to that material, the potency is denoted on the package and there is an expiration date.  As with any medicinal remedy the expiration date should be noted.

Again, if this material is exposed to the atmosphere it will adsorb.  I mean that is why it is ingested.  So logically, the moment it makes contact with the atmosphere it will adsorb. 

So your best bet is to observe the effectiveness.  If you see it has diminished then replace the strips and filters.  The shelf life for activated charcoal purchased at plant nurseries is designated from the date of manufacture.

here is some information on microfilters that use a charcoal stage:

Many microfilters may include silt prefilters, activated charcoal stages, or an iodine resin. Most filters come with a stainless steel prefilter, but other purchased or improvised filters can be added to reduce the loading on the main filter element. Allowing time for solids to settle, and/or prefiltering with a coffee filter will also extend filter life. Iodine matrix filters will kill viruses that will pass through the filter, and if a charcoal stage is used it will remove much of the iodine from the water. Charcoal filters will also remove other dissolved natural or manmade contaminates. Both the iodine and the charcoal stages do not indicate when they reach their useful life, which is much shorter than the filter element. If you are depending on the stage for filtering the water you will have to keep up with how much water passes through it.

[Arkcon]

   Surely there must be a way to test for this without requiring extensive equipment?

I'd bet not.  For industry applications, there may be ranges for absorption of some known compound, and a certain batch or grade of activated carbon, you can make a theoretical calculation, and determine about how much you need, or how long a small quantity will last, but that's it.  I figure, you test your final, post filtered product, and if it's not adequate, you reprocess with fresh absorbent.  Trying to see, what's been absorbed, unto a micro-porous surface, with anything less advanced than a scanning electron microscope, that I just don't see.

In my experience, there are two extremes.  I'll wear a facemask, with a activated carbon filter, whenever I work with hazardous solvents.  One company I worked for changed the filters with each day's use, they acknowledged that might be expensive and wasteful, but better safe than sorry.  Another company was less wasteful, and insisted you wait, until you noticed solvent leaking through, and then you could get a new filter.  A little bit unsafe there, but costs were an issue.

[Beaker]

The problem with the just-try-it method, is that for many useages, you can't easily see an immediate result.  The Tarni-Shield strips are a perfect example of this.  Testing that product in that way would mean that you'd be waiting months - which is not only impractical, but wasteful.

Ordinarily, the average person would think that in order to test whether a certain physical material is what it's supposed to be, you'd need specialized equipment to examine it on a molecular level.  And yet, there are special markers used to see if a currency bill is genuine, chemical tests for certain precious metals, etc...


I was hoping that something similar could be done with activated charcoal.  For example (and this is probably enormously incorrect - but try to get the spirit behind the idea), a solution consisting of a yellow fluid and blue particles, yielding a green color - and if applied to useable activated charcoal, would turn more yellow in color, the more blue particles were being adsorbed into the test material.

My point is that I would think that there must be a (relatively) simple way to test for adsorption in a more timely and obvious manner.

[Arkcon]

And yet, there are special markers used to see if a currency bill is genuine,

A rather poor example you've chosen there, but it does show where your thought process is coming from.  That is an iodine pen, looking for the starch used as sizing in computer printer paper, which the linen currency paper doesn't use.  Spray some genuine bills with laundry starch, if you want to make them non-negotiable at a place that relies on those pens.  'Tho most dishonest people would rather work that problem from the other end. -- and I can think of at least one potential reagent that might work, 'tho I won't be posting it here. There is no simple chemical test for the abstract concept of honest currency, despite the urgent need.

My point is that I would think that there must be a (relatively) simple way to test for adsorption in a more timely and obvious manner.

Adsorption is a molecular process, not a chemical reaction.  It doesn't form products, etc.  You could try to get the carbon to release it's absorbed products, but what are they, and how will you detect them? Look at this other thread on absorption:
http://www.chemicalforums.com/index.php?topic=23625.msg89733#msg89733