The effect of NaCl on the ability of an acid to protonate benzoate I've been doing several experiments using soda to quantify the amounts of caffeine and benzoate. Because of our methods of analysis, we had to decarbonate our soda. The experiment offered two ways for decarbonating the soda: shaking it or heating it. Then, to make sure all the benzoate in the soda is converted to benzoic acid, we add a small amount of $\ce{HCl}$ (to protonate it.)

Several years ago, I did a similar experiment to quantify the amount of caffeine. To decarbonate the soda, I added salt ($\ce{NaCl}$.)

I'm wondering if adding salt would be inappropriate in the more recent experiment. None of the lab procedures mention adding salt and, to me, this is the easiest way to decarbonate soda. Therefore, I'm thinking there may be a specific reason the salt method was left out of the procedure.

My thought is there could be some interaction between $\ce{Na+}$ and $\ce{Cl-}$ that could "neutralize" the $\ce{HCl}$ so to speak, making the protonation of benzoate less effective.

Perhaps it would make sodium benzoate instead of benzoic acid? Perhaps they just didn't think to add salt. Any thoughts on this?
Some salts added obviously will alter the pH value of the soda ($\ce{NaHCO3}$, for example), and others not (like the example provided by you, $\ce{NaCl}$). Changing the ionic strength by addition of salts may render your mathematical model to describe the composition of the analyte more complex.

Hence, let me I suggest an alternative to outgassing the soda: immerse the open container into an ultrasound bath.  This works rapidly, however ensure the container is widely open and may accommodate the foam briefly generated.  Otherwise, it may surprise you as a sticky geyser.  Second hint: gently approach the active regions in the ultrasound bath to moderate the gas evolution.

(Degassing solvents with ultrasound is a common preparation for HPLC, too.)