Discrepancies between the chemical abundance ratios (ΔX = X_opt − X_IR) as a function of their ratios: (a) 12+log(O/H) and (c) log(N/O) both derived from IR emission lines with HCM-IR, and (b) 12+log(O/H) and (d) log(N/O) derived from optical emission lines with HCM. For all plots we present Seyferts as blue circles, ULIRGs as green squares, LIRGs as magenta triangles, and LINERs as red stars.