[Xiaoling]

Thanks JGK. Whenever a certificate stated a purity value from TLC or HPLC, is that the purity of the salt or the free base? For instance in the previous case, the purity is 100% is the purity of streptomycin or streptomycin sulfate. Is it that everytime I see a purity value given, I can assume its the free base? Thanks for helping.

[JGK]

No, you cannot always assume that the purity value applies is free base. You have to consider all available information

However given the potency value you gave as 749 for the streptomycin base (dried). This value is within the range quoted in the USP for the pure material. I therefore assumed 100% from the TLC applied to the base.

(I'm not sure wether you got the correct potency units should it be µg/mg and not U/mg? the USP quotes potency in terms of µg/mg)

[Xiaoling]

The potency is indeed in units/mg. Actually, I found something from the USDA protocol regarding the calculation of both this problematic Penicillin and streptomycin (which is in unit/mg) but cannot comprehend it. Please refer to http://www.fsis.usda.gov/PDF/MLG_34_02.pdf page 21-22. As you can see, for streptomycin, they actually convert the units/mg to ug per mg. Which is quite confusing for me. Same goes to Penicillin. They convert the units/mg into percentage. Is the working correct? Please advise. Thanks 

[JGK]

The potency is indeed in units/mg. Actually, I found something from the USDA protocol regarding the calculation of both this problematic Penicillin and streptomycin (which is in unit/mg) but cannot comprehend it. Please refer to http://www.fsis.usda.gov/PDF/MLG_34_02.pdf page 21-22. As you can see, for streptomycin, they actually convert the units/mg to ug per mg. Which is quite confusing for me. Same goes to Penicillin. They convert the units/mg into percentage. Is the working correct? Please advise. Thanks 

The paper states pure streptomycin is 785 unit/mg yours is 749 unit/mg it is therefore 749*100/785 = 95.4% pure.

so the calculation should now be:

For 10 mL of a 1000 ppm STD (1 mg/mL, 10 mg/10 mL)

Starting at 100% purity subtract the percentage water content 100 - 6 = 94%

With streptomycin purity at 95.4%

you just need to use the following calculation =(10 x 100/94) *(100/95.4) = (10/0.94)/0.954

= 11.15 mg disolved in 10 mL

[Xiaoling]

Thanks alot JGk....Please help me ...
Q1) Whats the difference between Purity and Assayed.
Q2) In the following example, I need to prepare 1000ppm of Chlortetracycline. But what I have is Chlortetracycline Hydrochloride. MF is C22H23ClN2O8.HCl. MW is 515.34. Moisture content is 0.4%. Purity by HPLC is 83% and Assay (Brit. Phar.) is 97.3%.
I shall need 10mg of PURE Chlortetracycline. So should i divide 10 by 83% or 97.3%?

Q3)The purity 83% is it pure chlortetracycline or pure chlortetracyline hydrochloride? With or without water content?

Q4) After the adjustment with one of this % value, do i need to convert using MW data ? And adjust the water content?

Please please help . Thank you Thank you .

[JGK]

Thanks alot JGk....Please help me ...
Q1) Whats the difference between Purity and Assayed.
Q2) In the following example, I need to prepare 1000ppm of Chlortetracycline. But what I have is Chlortetracycline Hydrochloride. MF is C22H23ClN2O8.HCl. MW is 515.34. Moisture content is 0.4%. Purity by HPLC is 83% and Assay (Brit. Phar.) is 97.3%.
I shall need 10mg of PURE Chlortetracycline. So should i divide 10 by 83% or 97.3%?

Q3)The purity 83% is it pure chlortetracycline or pure chlortetracyline hydrochloride? With or without water content?

Q4) After the adjustment with one of this % value, do i need to convert using MW data ? And adjust the water content?

Please please help . Thank you Thank you .

With the Information you have:
Step 1: Subtract the % water from 100%
Step 2: The purity 83% is pure chlortetracyline hydrochloride (if it was base chlortetracyline it should state that), adjust the value from step 1 for the purity.
Step 3: Apply the % value to the target weight
Step 3: adust target weight for pure chlortetracyline content= x (mw chlortetracyline hydrochloride/mw chlortetracyline)

If you are unsure of terminology on CoAs I would suggest you first call/e-mail the maufacturer/supplier for clarification rather than assuming anything (or even asking an opinion from someone who has hot seen the document.  The primary rule is never assume anything that is not specifically stated.

[Xiaoling]

Thanks for your help and advice 

[ubin85]

Hi,

I have bought this from sigma.

erythromycin

potency: NLT 850µg/mg
water by karl fischer: NMT 10% (4.5mol/mol)
elemental analysis: 59.2% to 61.8% carbon
                             1.6% to 2.2% nitrogen
(anhydrous basis)


Can i use this to prepare my standard solutions for LCMS/MS to test my recovery of my sample?

[JGK]

Hi,

I have bought this from sigma.

erythromycin

potency: NLT 850µg/mg
water by karl fischer: NMT 10% (4.5mol/mol)
elemental analysis: 59.2% to 61.8% carbon
                             1.6% to 2.2% nitrogen
(anhydrous basis)


Can i use this to prepare my standard solutions for LCMS/MS to test my recovery of my sample?

I don't see why not, however I'm not sure what the abbreviation "NLT" means on the potency statement. That could affect your calculations.

[Marma]

Hi
I need to prepare antibiotic stock solutions of 10 mg/ml for Doxycycline hyclate and for Minocycline hydrochloride, crystalline (both purchased from Sigma). I would be really greateful if someone would help me with this..  I am a microbiologist, not a chemist or a pharmacist, so I have great troubles calculating this . I have tried for a long time, but I always get too confused, so I really hope someone can help me (if so, only by suggesting some litterature)!

Minocycline hydrochloride, crystalline:
MW: 493.94, water by Karl Fischer: < OR = 10% (3MOL/MOL) , Purity by TLC: > OR = 98%, Elemental Analysis (anhydrous basis): 54.5 TO 57.3% Carbon  8.2 TO 8.8% Nitrogen, Potency (anhydrous basis): 890 TO 950 micrograms minocycline/mg

Doxycycline hyclate:
MW: 512.94, water by Karl Fischer: NMT 5%, Solvent content: NMT 7% Ethanol by Gas Chromatography, Elemental analysis(anhydrous basis): 5.5 TO 6.1% Nitrogen, Purity by TLC: 98% minimum

[Marma]

Just to make sure - I need 10 mg/ml solutions of the active drugs.

[Arkcon]

In order to begin to solve this for yourself, you can first forget about the elemental analysis.  Now, if these reagents were 100 % pure, you'd know how to make a 10 mg per ml solution, right?  You'll need more, because you know there are slight impurities -- water, ethanol, etc.  Can you try to first off, decide what info to use, to determine how much more you need?

[Marma]

Thank you for answering! I will try to explain where I get confused.. (and yes, if they were pure even I could figure out how to dissolve them;))

I have tried to use this formula: Potency = Assay purity * active fraction * (1-water content)

For minocycline, where I get in trouble is what the potency on the label refers to, since it is on anhydrous basis. In the formula above, you use the water content to calculate the potency.. Also, how do I know the active fraction? And should I consider Minocycline hydrochloride as one, or seperately (exclude the HCl) ? I guess I should calculate the lowest and highest possible potency since the values for water content and potency are within a range.

For doxycyline, I am confused about the ethanol content, since the formula above only tells me to exlude water in the potency calculation. Shouldn't ethanol be excluded also?

Thanks again for helping me out, I really appreciate it 

I hope this wasn't to confusing..

[Marma]

Is there anyone who can help me with this?? It would be tremendously appreciated 

[Arkcon]

It really depends on your application.  If you're in a cGMP analytical laboratory, there are rules to follow, detailed in the correct pharmacopeia (USP, EUP, JP, and others.)  If you're following someone else's research, you should follow their protocol, which may be in their original citation, or referenced in it.  You might also want to ask whoever gave you access to these stock antibiotics.