Estimation of nickel ions I was doing experiment of estimation of copper and nickel ions by means of volumetric and gravimetric analysis respectively.

Suppose we analysed $\ce{Cu^2+}$ ions by precipitating with $\ce{H2S}$
But still there are some copper ions remaining in solution.

Is there possibility that they ($\ce{Cu^2+}$) can form complex with DMG
and interfere with Ni-DMG complex.
Copper can form a stable DMG complex (if it is there in the mixture in high concentration), it may also effect the color of the resultant Ni-DMG complex. Just go through Vogel's quantitative inorganic analysis book once.