It depends on Expiry date. Some chemicals have no expiry. These chemicals you can change unless and until there is no physical change, eg. color, liquification etc. At the time of assay you have to check  pH, moisture contents etc.

There is no \\simple answer as many factors apply,   Age--many chemicals wii decompose over time or will react with air components.  How many times have containers been opened?  Chemicals such as simple ethers will form O--O--O.  I had a reaction explode when using "old" dioxane due to this.  Have the color of the chemical changed indicating decomposition.  Does the chemical look wet or swollen indicating absorption of water?  Usuage--If the chemical is used for pH adjustment it may have a longer shelf life than a chemical which is measured out by weight.  If NaOH or Carbonates are used to form solutions used to alter pH monitored by pH measurements or indicators they can be used longer than if an quantitative solution by weight is being made.  If reagent for reactions, slight impurities from breakdown of molecules can increase side reaction products. 

Instead of disposal, it might be better to use up opened bottles first and then opening up a new bottle than to always open up a new bottle and having many partial bottles hanging around. 

Other considerations apply.  Look at the needs of the lab and then see what can be done to minimize open  bottles and the requirments needed by projects as to age and condition of chemicals used.  Then decide on disposal requirements

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Expiration date of chemicals depends mainly on many factors from the conditions of storage and processes of usage. Except that, the manufacturer's instructions are supported.

Thanks for your comments. Here I am not talking about saving any chemical which is in a opened container, which shows physical change, color, liquification etc. for future use. As Wayne Morris mentioned, solvents like Ether, dioxane etc can go bad with time and we wouldn't even notice it unless it is tested analytically.

But here I am referring to unopened containers of solid chemicals which does not come with an expiration date and perfectly in usable condition. I wouldn't agree to discard these precious chemicals just to comply with some guidelines.  As Michael Pach pointed out, I am sure it is just lack of understanding between the bureaucrats and scientists. 

First question arises, why do we need chemicals? Certainly to find the results for unknown sample. What if known sample i.e standard samples are analysed with these chemicals. If results are accurate  that means chemical is still in better condition else needs disposal. Probably that is the best method to determine the purity of your chemicals. However, you have to experiment with every closed jar. We call this method Finding the Real Parents.

There must be one more approach, but i am not sure about it, knowing the half life of various constituents? If the chemicals have long half life and are in inert condition, one should not worry.

Its depends upon your uses.

As per iso you have to manage Media and Chemical inventory, Uses and Discard Record.

You can use your chemical and media before expiry, after open if there any change in appearance then you have go validation of media and Chemical with Records

Our 10M NaOH bottle opened Aug 2017 seems to have been affected. Its opened every few days. Could its molarity or other properties be affected by air contact? All buffers or reagents made with it seem dysfunctional.

I think its depend on whatever the dates of expiration and also the instruction given by the manufacturer. If the chemicals not follows date and instruction then you can go for colour, odour and pH if again it will not supported then it will better to change it by considering safety and efficacy

Look at the label of COA. It should say the date of expiration. That is it.

Someone might use expired chemicals only for teaching purposes but again a knowledgeable person should confirm the activity.

As a rule of thumb, you should never use expired chemicals.

There are three labels that are mentioned on any chemical package, Expiry Date, Shelf Life and No label on its life or expiry. There is no issue with Expiry and Shelf Life. But, any container without these two makes one confused. We long for such kind of questions. You will see that NaCl bottle of one brand mentions shelf life and other don't specify it. So, this is what suites the manufacturer best.

In such a situation follow the best practices that helps the chemical to remain free from contamination,. Don't open the container too frequently; use inert device while drawing or shifting the chemical; all such kind of practices shall enhance the shelf life of chemical. See do's and don'ts while dealing with CRM/SRM. Always keep a check on its physical properties of chemical after opening the container. Generally, the chemical shelf life is 5-6 years, where not specified. I have seen agar containers with expiry mark, and you keep it open for a while its gone.

Hi All, We are having 12 years old carboxymethyl cellulose (CMC) in our laboratory. I wonder, should I use this very old chemical or not. Appreciate your valuable suggestions.

Thank you.

Concerning Seema's question. While CMC is stable when stored properly there is a chance over that period of time that contamination could have occurred. While it may still be ok for certain non-critical applications, CMC is relatively inexpensive and unless you can determine that it is "fit for your use" my suggestion would be to purchase new. Consider the cost of a failed experiment, or any downstream ramifications that could result due to contamination. I would certainly NOT recommend using it for any food or pharmaceutical preparations.

Dear Dr. Thomas,

Thank you for your valuable suggestion.

Regards