Fig. 2. Optimization of mobile phase for resolution of malate and citrate nickel complexes. (A) Effect of the mobile phase composition on the chromatographic resolution of nickel citrate and nickel malate. In each case, enough amount of an apolar solvent (hexane or toluene) was used to fill up the indicated percentage of alcohol (methanol, ethanol or propanol). The horizontal line indicates the threshold of chromatographic resolution. (B) Effect of the mobile phase composition on the retention times of nickel citrate and nickel malate. Solvent mixtures: hexane/methanol (black bars), toluene/methanol