I need to prepare 10ml of 1000ppm(ug/ml) of streptomycin stock solution. So i need to weigh out 10mg of pure streptomycin and dissolve in 10ml of water. But I have with me a Sigma Streptomycin sulfate with formula C21H39N7O12. 1.5H2SO4 and MW=728.69, moisture content of 6% and potency 749units streptomycin base per mg on dried basis. How to calculate how much of this streptomycin sulfate to weigh which is equivalent to 10mg of pure streptomycin? Do i have to convert unit/mg into ug/mg? Anyone please help?
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Re: convert units/mg to ug/mg (potency)
Originally posted by xiaolingI need to prepare 10ml of 1000ppm(ug/ml) of streptomycin stock solution. So i need to weigh out 10mg of pure streptomycin and dissolve in 10ml of water. But I have with me a Sigma Streptomycin sulfate with formula C21H39N7O12. 1.5H2SO4 and MW=728.69, moisture content of 6% and potency 749units streptomycin base per mg on dried basis. How to calculate how much of this streptomycin sulfate to weigh which is equivalent to 10mg of pure streptomycin? Do i have to convert unit/mg into ug/mg? Anyone please help?
Pure streptomycin = MW 728.69  147.12 = 581.57 ????? (check this).
Therefore weigh out 10mg x 100/94 x 728.69/581.57 = 13.3mg plus any allowance for different activity factors.
Also, it is important to understand that you need to make this up to 10mL, for example in a volumetric flask, rather than adding 10mL of water, as the material will have a small but significant volume.  This is the difference between having a known amount in a known volume, as opposed to having a known amount in an unknown volume.
Hope this helps, sometimes it is worth sitting down and spending a few hours really coming to grips with these dilution questions, otherwise you can struggle with them for years, and never be confident of your results.
Good luck with your studies.

Re: convert units/mg to ug/mg (potency)
Originally posted by xiaolingThanks a lot Mrs X. But can you please tell me what is activity factor? Is that the potency?
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Re: convert units/mg to ug/mg (potency)
I am having the same problem!!
So if you have a sample of streptomycin sulfate that has activity units of 730 units per mg; then how do I calculate the molar concentration so I can then determine the activity against a bacterial strain?
Is it as simple as 730/1000 for the 'real' mass you are using?
Or a division of the real mwt including sulphate by the 730??
Heeeellllppp
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Re: convert units/mg to ug/mg (potency)
Hello, also I have encountered a problem concerning streptomycin sulfate. I have to calculate a solution of 7 % streptomycin sulfate (dissolved in ionized water) into ion strength, that is mM. I have used streptomycin sulfate from Sigma with product description similar to the above mentioned (in this thread): Mw of 1457.38 g/mol; H2O content: 6,5 mol/mol; 764 units streptomycin base per mg (not sure what that means). I am dumbstruck!
If would appreciate if a kind soul would give some help!
/Jim
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Re: convert units/mg to ug/mg (potency)
In addition to adjusting for the H2O content and sulfate, you may also need to apply a conversion for IU to ug : theoretically, 100% pure anhydrous streptomycin sulfate contains 798ug streptomycin base, and the Third International Standard for used for determining potency is 785 units per mg sulfate. Therefore, you need to multiply the I.U. value for your material by the ratio 798ug/785IU to obtain ug streptomycin base per mg streptomycin sulfate weighed. In the above example,
749IU x 798/785 = 761ug/mg
or 76.1% streptomycin base. Adjusting for moisture, 1000ug  6% = 940ug anhydrous sulfate x 761/1000 = 715ug pure streptomycin base for each mg of sulfate weighed.
Hope this helps...
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Originally posted by Unregistered View PostRe: convert units/mg to ug/mg (potency)
In addition to adjusting for the H2O content and sulfate, you may also need to apply a conversion for IU to ug : theoretically, 100% pure anhydrous streptomycin sulfate contains 798ug streptomycin base, and the Third International Standard for used for determining potency is 785 units per mg sulfate. Therefore, you need to multiply the I.U. value for your material by the ratio 798ug/785IU to obtain ug streptomycin base per mg streptomycin sulfate weighed. In the above example,
749IU x 798/785 = 761ug/mg
or 76.1% streptomycin base. Adjusting for moisture, 1000ug  6% = 940ug anhydrous sulfate x 761/1000 = 715ug pure streptomycin base for each mg of sulfate weighed.
Hope this helps...
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Originally posted by adios View Post@ Mr.Guest Do you have any record of info or reference source about streptomycin free base content in 100% pure anh.and std I.U. for potency for salt;etc etc actually i needed to know all this info  so that i could apply the same conversion protocol in case of potency for kanamycin.
http://apps.who.int/iris/bitstream/1...WHO_TRS_36.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2554118/
You are welcome to post back if you require further info
You will need to check the protocol for kanamycin if it is different from from the various forms of sulfarsphenamine
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Originally posted by mogalsadiq View PostHello I also a same problem we prepared a stock solution 40 % in a tank we dose this solution 20 ltrs per hour to effluent flowrate is 6000 ltrs per hour then how we adding the solution in ppm?
This analysis is likely wrong, but if we assume 40% is volume/volume and that volumes are additive (both assumptions likely wrong), then the active ingredient is 8 L/h, and the output mixture is 6020 L/h or 8 L/6020 L x 10^{6} = 1330 ppm.
That figure could be substantially in error depending on what basis the 40% stock is computed, what kind of ppm you want, and the densities of the stock solution and effluent. With better information, we could give a better answer.
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