so ... you have a solution containing 1000ppm , that means for every million gms of solvent there are 1000 gms of X , so 1 liter contains 1gm
0.5gm powder ...
you want a million gms of this powder to have 500 gms of X
so 1 gm powder will have 0.5 milligrams of X
0.5 gm powder will have 0.25 milligrams that's 0.00025 gms
one cc of your solution contains 1 milligram X
A quarter of a cc (ml) 0.25 milligrams
you need to add one quarter of a cc of solution
