Hello,

is it 50 mg/ml or 50 ug/ml (microgram/ml) ? If it’s equal to ppm so it should be in ug/ml

anyway, to prepare medium contain antibiotics 100 ug/ml, I will prepare antibiotic solution by this procedure :

Stock Concentration: 100 mg/mL dissolved in H2O (e.g. 1g powder in 10 mL H2O), stored at -20°C in aliquots

Working dilution: 1/1000, so you have to put 500 µL stock solution in 500 mL of your medium, for example. Your final working concentration is now 100 µg/mL

goodluck :)

Thank you @wiwiek

C1*V1=C2*V2