Staining, Histochemistry and Histotechnology
(Frequently Asked Questions)
Dr. John A. Kiernan
Department of Anatomy
and Cell Biology
The University of Western Ontario
Molecular sieves for making anhydrous solvent
Which type of molecular sieves are used for making anyydrous acetone or alcohol, and how much should I put in the bottle?
The molecular sieve to use for acetone is type 3A, mesh 8-12. EM Science Catalog # MX1583L/1 for 500 g or /3 for 2kg.
Before using a molecular sieve, you first have to determine which one to use. Type 3A if for unsaturated hydrocarbons and polar fluids. These include methanol, ethanol, and acetone. The 3A refers to the size of the molecule it can absorb. In this case, less than 3 angstrom. Molecular sieve 3A has an absorption capacity of 22% by weight.
To dry a liquid, add a slight excess of drying agent.
Next, a little calculation. If the information isn't on the label, call your vendor and retrieve a C of A (certificate of analysis) for the lot of solvent you're using. There should be a spec for water content. This value is the moisture in the bottle upon release. An opened bottle will have higher moisture, depending on how hygroscopic the reagent is. Let's use methanol, which is very hygroscopic, as an example, with the C of A stating that the water content is 1.0%, which equates to 4 ml in a 4 liter bottle. 4 ml of water is equal to 4 g of water. This is 22% of (4 X 100 / 22) = 18.18 g. For excess use 20g of molecular sieves.
Mix thoroughly and allow the liquid to stand. After a few minutes the drying agent settles to the bottom of the container. Separation can be completed by decanting or filtration (suction filtration would work best and fastest ). How often you would dry a solvent out is dependent on application, use, and humidity.
TIP: Depending on application and specifications required, the use of molecular sieves may eliminate to need to purchase expensive super dry reagents.
Rande Kline & Joe Daniels
Technical Services, EM Science