Liquid chromatography (LC) with a hydrophilic polymer gel column and an aqueous mobile phase is a high-performance separation method based on solute partitioning in a polymer-based ATPS. LC with ATPS, ATPS-LC, provides unique methods for separation and/or enrichment of ionic solutes because both phases of ATPS can dissolve them in a charged state without any special derivatization. This chapter describes the principles and practical applications of two ATPS-LC techniques developed for the separation of metal ions, multistep pH-peak-focusing LC, and enrichment of anionic solutes, partition/ion-exclusion chromatographic ion stacking (PIEC ion stacking). It will be demonstrated that multistep pH-peak-focusing LC is useful for separation and enrichment of rare earth metal ions using the mobile phase containing suitable extractants. Each metal ion is concentrated at the respective pH border in the LC column formed by a stepwise pH gradient elution in a manner similar to multistep pH-peak-focusing CCC. However, the metal enrichment and separation performance of LC with a hydrophilic polymer gel column is much better than that of CCC. PIEC ion stacking is a method that enables one to highly concentrate ionic solutes by the synergism of the effect of background co-ion on the partition of target ions into the polymer gel phase and ion-exclusion effect from the gel phase. A novel analytical methodology for simple and efficient online preconcentration of trace inorganic anions in reagent-grade salt samples for ion chromatographic analysis will be proposed using PIEC ion stacking with a hydrophilic polymer gel column containing fixed anionic charges.