How would you properly measure the mass of a liquid

You can consider the density of the water. Thus, in order to properly measure the mass of a liquid, we can first get the volume and density of the liquid material or substance. We can firstly utilize the formula to get the mass from deriving the set formula of density to mass: Since density is mass over the volume,
1.  D=m/v
2.  We can transmute the formula to m = dv
3.  Mass is density times the volume

Because you ate playdough

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck