Expiration dates ! - (Aug/09/2007 )
hi guys,
how do u know that your chemicals are expired!!
i noticed that some chemicals in our lab are old and when i tried to find the date of expiration, there was nothing !! 
we tried one chemical and compare it with a new one, the readings were different !!!!
how do u know that your chemicals are expired!!
i noticed that some chemicals in our lab are old and when i tried to find the date of expiration, there was nothing !!
we tried one chemical and compare it with a new one, the readings were different !!!!
I guess it depends which chemicals you meant. Many (or most?) salts have no expiration date (actually I used some common salts (e.g., KCl) that were 20 years old. Enzymes you have to try out if they work, but I guess if they are handled appropriate and rarely they can be used surprisingly long. Most problems will occur with contaminations and impurities after long use.
Different reading can have various reasons, not only old chemicals (e.g., differences in concentration).
In my experience, many expiration dates - when specified - are placed long before the real expiration of a product.
NaCl ar ethanol have expiration dates that cover some years after purchase, but I'm sure they won't suddenly change their chemical properties after those date.
This is not true for other properties, such as purity, humidity, loss of weight etc. even if I believe that these depende on the way you handle your chemicals more than on their expiration date.
E.g. if you take your ethanol and make from time to time aliquotes, you will introduce less impurities than taking a bit every time you need it directly from your stock.
The decision of using of an expired reagent depends on how much you know about the chemistry of your reaction and how critical is that reagent in your protocol. You can always decide to make a previous assay to check if it's effective or not...
we tried an amino acid (new and old) with the same concentration !
agree with u ila at this point, chemistry issues are important
Sometimes you can check the manufacturer's website for starters to get an idea for when products will expire. For instance, SIGMA posts Certificates of Analysis on their products. If you type in the catalog number and then search by lot number, you can find information on your product. Or, you can call their technical support and ask as well. Sorry, I know that only helps if you have bought a chemical, rather than prepared the reagent yourself, but the other replies seem like good suggestions as well.
for amino acids, they're bought of course !
What kind of a measurement (reading) did you do for this amino acid? I guess that the storage conditions are also relevant. Storing in a refrigerator or in a dessicator. Also: did you check the % purity in the label of both (the new and the old) amino acids. Sorry to ask such a question, but sometimes I have forgot to do so with other substances, and then when double checking things finally work.
I don't know whether it is true or not.....
The amino acid (old) may absorb the moisture from air and become heavier...depend on storage
Therefore when you measure the same amout of old and new, you will have less concentration of the old amino acid compare with the new ones.
Hope this may help.
the old bottle of amino acid contains little powder and mostly is in form of clumps...
clumps is due to humidity.
Do you have a lyophiliser in your lab? It's an interesting technique to restore water free powder. without damaging by heating.