[CopperSmurf]

This might seem silly, but I always get into trouble when it comes to ppm. 
I used very dilute solutions for liquid/gas GC coupled with a mass spec for analysis and one of the standard concentrations given to me was in ppm. The problem is that ppm is dimensionless and it was not dissolved in water, it was in methanol with a given density in g/mL and I know how much (in mL) I put in there. So, how would I convert this solution in ppm into something like g/mL?

P.S. there was absolutely no water in any of this.

[sjb]

Depending on what ppm you're using (w/v, v/w, w/w, v/v) simply convert. As your solutions are very dilute, you may be able to assume the density is that of pure methanol.

[Mansouri]

as you know, 1ppm eq. to (1mg/1 Liter) or (1mg/1000 ml),
so if you have density you most convert it to ml by (d=m/v), then calculate your favorate ppm conc.
have a fun.

[sjb]

No, 1 ppm is not equivalent to either 1mg/1 litre or 1mg/1000 ml. This may be close to being true for dilute aqueous solutions, but is not something that holds for everything.