Multi Species Problem (mass fraction)
 

i have multi species problem with initial concentration. It is basically a Continuous flow PCR proble. for example:
P1 species has initial concentration 3x10^-7 mol/m^3
properties of P1 species is taken as water (molecular mass =18 and density = 1000 kg/m3)
Volume of fluid is 5.3x10^-6 liter.

If i calculate mass fraction of P1 species with following formula:
w (mass fraction = molar concentration * Molecular mass/density

mass fraction of species P1 = 5.4x10^-9

Is it correct? because mass fraction of all species dont give 1. Do i need to add main fluid (water) + species (5 species) to configure problem? Now i am considering only species in my problem.