How to meausre ion interferences in solution? Is there a way to quantitatively measure the interference of different metal ions in solution? I plan to measure concentration of Pb(II), Fe(II), and Cu(II) in solution together using a spectrophotometer. 

I know that I can put multiple samples of two ions together to test for the interference trends/effects, but can I do this for all three? e.g. measure interference effects of both iron/copper on lead? Or are there too many variables to measure concentrations?

If not feasible, are there other accessible ways (besides mass-spec) to measure multiple concentrations of all three at once? 

EDIT: I already plan to measure concentrations using reagents, specifically Hach TnTplus 850 and 858, and Hach CuVer 1, as they seem easy to get and use. My purpose is to accurately measure concentrations of one ion when in the presence of two other interfering ions.
What you can do is to add a reagent which forms a highly coloured complex with one of the metals, this will allow you to make a measurement which is good for one of the metals. You may need to do three different experiments on three seporate aliquats from the same solution.

For example for the iron, I would suggest that you use 2,2'-bipyridine, or 2,2'-bipy as it is sometimes known. This forms a very deep red complex with ferrous iron. This would allow you to measure the iron.

You would need a series of calibration samples with different amounts of iron, please do be aware that the matrix can sometimes interfere with this measurement. I have found that oxalic acid does inhibit the formation of the iron tris bipy complex.

Maybe you should read this paper which is about 2,9-dimethyl-4,7-diphenyl phenanthroline. This is a reagent which has been reported to be good for copper determination.