Multivariate optimized experimental conditions were established for the determination of nickel(II) in 92 grape samples after complexation with ammonium piperidine dithiocarbamate (APDC) and ammonium morpholine dithiocarbamate (AMDC). Differential pulse polarographic (DPP) studies of the wave characteristics indicated that it is of the catalytic hydrogen wave (CHW) type sensitive to pH, concentration and scan rates. A single, sharp peak obtained at −1.22 V allowed for the trace determination of nickel(II) in the range of 3.2 × 10−6 to 1.17 × 10−3 M with a linear calibration and a detection limit of 1.8 × 10−6 and 2.7 × 10−6 M for APDC and AMDC respectively. Mechanistic aspects between APDC/AMDC and nickel(II) were confirmed with cyclic voltammetry and supported by theoretical calculations. The DFT calculations of piperidine adduct reveal a smaller HOMO–LUMO energy gap than morpholine adduct, suggesting that piperidine adduct has a greater tendency to act as an electron donor.