problem in preparing minimal media containing chromium - (Sep/17/2017 )

hi, all. I am facing problem in the calculation to prepare minimal media (composition below) that contain 10 ppm chromium. I want to prepare 100 ml minimal media contained 10 ppm of chromium. can anyone help me to do that?

composition of minimal media

solution A

KH2PO4 0.3gr

Na2HPO4 0.6gr

NH4Cl 0.2gr

NaCl 0.5gr

DI water ~80ml

solution B

glucose 0.8gr

MgSO4.7H2O 0.01gr

agar 1.5gr

Di water ~20ml

if I add 10 ppm chromium in solution A, is my media already contain 10 ppm of chromium?

thanks in advance.

No - if you add to a final concentration of 10 ppm to the 80 ml, and then add the extra 20 ml to make your final solution, you will have 8 ppm as a final concentration.

If you want to get 10 ppm in the 100 ml, you need to add a correspondingly higher amount to solution A. The good thing is, the amount you add will not change so long as you have calculated if for the 100 ml solution. For instance as 10 ppm is 0.01g in 1000 ml - for 100 ml this would be 0.01/10=0.001 g (because 100 ml is 1/10th of 1000 ml). If you added this amount to the 80 ml, then topped up to 100 ml with solution B then your concentration would be correct.