Frequently Asked Questions (FAQ)
Please explain the wide variations in hygromycin purity. And why does activity vary between lots from the same company ?
Hygromycin B is a compound very difficult to purify. The degree of purity achieved can vary widely between different production batches. Since lots have different purification levels, most suppliers list their hygromycin as "superior than x% pure" to accomodate for batch variability .
Why are some suppliers providing hygromycin as a defined quantity by mass (i.e. 1g , 5g) while others supply it in units (i.e. 1 mU) ?
Arbitrary units provide no information on the product impurities, whereas mass and purity are scientific standards used for any fine chemicals. There cannot be a standard universal unit scheme for measuring hygromycin activity since any measure of activity relies on a biological test (i.e. how much product is needed to kill an arbitrarily chosen organism).
How can I roughly assess hygromycin purity ?
The color of a hygromycin solution is a good indicator: the clearer it is, the purer. Therefore, "caramel colored" solutions are of inferior grade. The color difference may not be very dramatic with a freshly made low-concentration hygromycin solution, but with some aging the difference is striking:
* Impurities present in the hygromycin preparation are easily visualized because their oxydation over time darken the solution. To speed up this process for a quick visual test, the solution can be artificially aged by heating-up the solution for a few minutes at 60°C.