“…It indicated that these IP reagents have enough abilities to form ion-pair with the dye components in the ink entries, but the retention times of the dye components were relatively shorter and the chromatographic peaks were sharper when TBABr was used as the IP reagent, so TBABr was selected as the IP reagent for the IP-HPLC analysis of the red stamp-pad ink entries. The buffer solutions (pH 7.0) with different concentrations of TBABr from 10 to 80 mmol/L (10,20,40, and 80 mmol/L, respectively) and the effect of pH value (5.0, 7.0, and 9.0) on the separation of the ink dye components were also investigated individually. Considering the separation, selectivity, and retention time of the dye components in the red ink pastes of seals, the mobile phase was selected as follows: 20 mmol/L TBABr buffer solution (pH 7.0) with ACN as organic modifier for the IP-HPLC analysis and a programmable gradient proportion of the buffer and ACN (from buffer/ACN v/v = 45:55 to 5:95 in 12 min) at the flow rate of 1.0 mL/min was used.…”