To adjust the equilibrium pH, you can add a buffering agent to the system. For example, if you need to maintain a pH of 3-4 for the acidic extractant, you can use a buffer such as acetate buffer, which has a pKa of around 4.76. Similarly, if you need to maintain a pH of 9-10 for the basic extractant, you can use a buffer such as carbonate-bicarbonate buffer, which has a pKa of around 10.33.

Here are the general steps to adjust the equilibrium pH using a buffer system:

Choose a buffer system with the desired pH range for your extraction experiment.

Prepare the buffer solution according to the protocol.

Adjust the pH of the buffer to the desired pH range using a pH meter.

Add the buffer solution to your extraction system in the desired concentration.

Mix the extraction system thoroughly to ensure uniform pH throughout the solution.

It's essential to validate the buffer's performance under the specific conditions of your experiment as the buffering capacity of the buffer may be affected by the presence of other components in the extraction system. Therefore, it's recommended to perform a blank control experiment to evaluate the buffer's buffering capacity and the potential interference with the analysis.