Hasnaa Mahmod If you scroll down on that Sigma Aldrich page you will be able to obtain a Certificate of Analysis (CoA) for the lot number you have purchased. The purity of the lot you have will be stated on the CoA and this can then be used to determine the potency.

You also need to calculate the active fraction (the portion of the molecule you have that is active agent) which can be determined as mw (antibiotic only) / mw (complete salt) [this is 100% if you bought the pure salt of ciprofloxacin rather than the hydrochloride]

Lastly you need to determine the water content, which should be listed on the CoA. This will be 0 for pure salt, but the hydrochloride is a monohydrate, so will have a water content >0.

Once you have all of these values you calculate the potency as:

Potency = (Assay purity) * (Active fraction) * (1-Water Content)

Hope that helps

Hi Dory Nicoletti

Depending on the values provided by the manufacturer in the certificate of analysis, you would normally take the water into account within the "water content" component of the calculation and only compare the HCl vs pure salt for the active fraction. Some manufacturers provide a purity value determined by mass balancing and these often include the water content within the calculations performed. Usually those manufacturers will provide a method at the end of the CoA that can help you to determine if this is the case or not

Hope that helps