Hi there,

Ampicillin and Kanamycin usual working concentration is 50µg/mL (stock x1000 in water)

Tetracyclin and chloramphenicol usual working solutions are 12.5µg/mL and  25µg/mL respectively (stockx1000 in Ethano

The working concentrations may be increased if more stringency is required for selection.

Hi there,

The efficiency of selection on ampicilline is actually very dependent on the structural features and on the copy number of the plasmid, on the bacterial host as well as on the duration of the experiment to be run (ampicillin is actively degraded during the selection phase therefore its concentration is going down with time). 50µg/mL is the minimal dose (I usually do 100µg/mL for E. coli) but it may be up to 500µg/mL if stringent selection is required.

And your calculation is good but to simplify the pipeting just let's say you have prepared a x1000 stock solution so for preparing XmL of LB you have to add XµL of the x1000 stock solution.