You need the concentration in #g*L^-1#, and convert this to #"ppm"#. How?
Explanation:
#"ppm"# as you know is parts per million; literally #"milligrams per litre"#, i.e. #10^(-3) g*L^-1# (ppm because there are a million mg in #1*L# of water). It is typically used for trace quantities, and the density of the solvent (usually water) is almost identical to that of the pure solvent.