An improved “heart-cut” column-switching method combining ion-exclusion column, monolithic anion exchange concentrator and capillary anion-exchange column is developed and successfully applied for the determination of inorganic anions (Cl−, Br−, NO3− and HPO42−) at trace level in weak acids. The quantitative determination of selected inorganic anions in the samples of fifteen weak acids and hydrogen peroxide are accomplished with analysis time of 45 min per sample. The obtained limits of detection (LODs) are in the range of 2.1–32.6 ng/L based on the s/n = 3 and injection volume of 50 μL. RSDs for retention time and peak area were all ≤1.89%. A spike-recovery study was performed under these conditions and satisfactory recoveries between 85.3 and 103.9% for all studied anions were obtained.