I prepared rifampicin (150 mg/ml stock) in methanol and stored at 4 C but after some day methanol gets evaporated so it makes difficult to pipette out rifampin for next use. If i add more methanol so it will change the concentration of rifampin from 150 mg/ml to something else kindly suggest for this to reuse the same antibiotic with 150 mg/ml concentration.
It appears that the vial you are using is not air tight. We prepare stock solutions that stay good through a full whole year and have never had a problem of evaporation from screw capped vials. Just curious what container are you using to make the standards?
if methanol is evaporated, your stock was 150mg/ml so just see how much volume is there and makeup it to 1ml (if it was 1ml in your stock) or volume that was in your vial after your last use. possibly it will not change the concentration.
Thank you Anubhav...... but I know very well whatever you explained. My problem is not that. I am using Rifampin from MP biomedicals which should be dissolved in methanol but it is not easily pipettable for 150 mg/ml stock some amount is going to stick to the wall of tip so I can not exactly add methanol to maintain the same concentration (150 mg/ml stock).
Thank you Manish.. I am using 1.5ml microcentrifuge tubes from Thermofisher for 150 mg/ml stock solution and it is air tight.
Kindly tell me what concentration of rifampicin you are using and with which solvent ?
Is methanol ok for rifampicin?
If it helps, we prepare 50 mg/mL solutions in methanol 100%, but storage is at -20 ºC instead of 4 ºC.
https://www.goldbio.com/documents/1088/Rifampicin+Stock+Solution.pdf
https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Product_Information_Sheet/1/r3501pis.pdf
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