pH adjustment

[fractionated]

Why do we need to adjust the pH of the liquid sample to less than 2 prior to hydrocarbon extraction?
Thank you

[Johnny Rod]

Either to protonate acidic species and make them hydrophobic so they extract into the solvent, or to make basic species ionised to keep them in the water phase. So it depends what you're trying to achieve.

[Don Shelly]

Johnny Red is correct. In the case of heavy fuels such as Diesel and kerosene, you are protonating fatty acids.

[fractionated]

thank you for your reply. But why do we have to include fatty acids in TPH extraction when the aim is to extract the hydrocarbons present in the liquid samples?

[Don Shelly]

If your goal is to extract fuel, fatty acids are part of that fuel.

[fractionated]

thanks for the reply. To my understanding, fatty acids are one of the metabolic products of hydrocarbon degradation my microorganisms. if we include them in the total hydrocarbon extraction, will this not create a bias in measurement?

[Don Shelly]

Some refineries actually add fatty acids to the heavy fuels that that produce. I have no idea why. Try extracting a "fresh" diesel fuel with and without pH adjustment and you will see for yourself.