Spectrophotometric determination of copper concentration

Context:

A typical lab experiment involves the addition of ammonia in excess to solutions of copper(II) to produce a complex ion whose absorbance at roughly 610 nm varies by the concentration of copper in solution.

Question:

Why is it less practical to simply test the aqueous solution of $$Cu^{2+}$$ rather than complexing it first with ammonia?

Thoughts:

My thoughts on this begin with the Beer-Lambert law: $$A =\epsilon lc$$

If the molar absorptivity of the ammonia complex in the visible spectrum around 600 nm is greater than that of the aqueous complex, [1] then small changes in concentration of copper can be differentiated by large changes in absorbance. This increases the sensitivity of spectrophotometric methods of determining copper(II) concentrations.

References

• If you have data that indicate the absorptivity is higher, you answer is correct. But you might be missing the higher solubilization as a small component to this as well. – Lighthart Aug 14 '15 at 22:02