What is the significance of ph in hplc

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However, due to the reduction in background conductivity of the mobile phase in the suppressor, the Na ions in the mobile phase are replaced by H ions. Consequently, the mobile phase suppressor eluate during detection becomes carbonated water, which is weakly acidic with a pH of 5 or 6. As organic acids have carboxyl groups, the pKa is approximately 4. The diagram shows the differences in peak response for acetic acid and formic acid using both a carbonic acid- and boric acid-based mobile phase.

The boric acid-based mobile phase becomes borated water with pH 6 or 7 after passing through the suppressor. Fluoride, acetic acid, and formic acid samples were prepared with the same concentration.

The boric acid-based mobile phase achieves a higher peak response for acetic acid and formic acid than the carbonic acid-based mobile phase. In addition, it can be seen that the change in response is larger for acetic acid than for formic acid.

This is because the pKa of acetic acid and formic acid are approximately 4. Because the dissociation increases as the mobile phase pH deviates further from pKa, acetic acid, which has a higher pKa, is more susceptible to changes in pH due to switching from a carbonic acid-based mobile phase to a boric acid-based mobile phase. Please confirm that JavaScript is enabled in your browser.