"In all experiments, NAC (final concentration: 20 mM, unless otherwise specified) was dissolved in H2O, and pH was adjusted to 7.4 by adding NaOH. Aliquots were stored at –20°C for 1 month maximum." i think H2O is better than DMSO. but given the maximal concentration, H2O is still unmet.

Pilipow, K. et al. Antioxidant metabolism regulates CD8+ T memory stem cell formation and antitumor immunity. JCI Insight 3, e122299.

NAC is water soluble, so it is easy to use in any solution. I would be careful with standard buffers, since many proteins and vitamins that are added to the buffers make ROS themselves (sugar, for example). Depending on the cells you are using, consider that they may not take NAC up at all, it may work only on the outside of the cell.

Since NAC is acidic, be sure to buffer your solution to a neutral pH with NaOH, to not add an additional stress.

I used an end-concentration of 2.5 mM, but I had packed RBC.

You can dissolve NAC either in Water or in DMSO upto 100mM (stock). I use 100mM stock in DMSO. Optimum concentration of NAC would vary from cell line to cell line. Usually 500uM to 1mM of NAC in the cell culture works with most of the cell lines.

I recently prepared a another batch of NAC. It worked well as well.

(1) Dissolve the NAC power in D-PBS (cell culture level) to a stock concentration of 150mM

(2) Adjust the pH to 7.2-7.4

(3) Filter it through 0.22um sterile syringe filter

(4) Aliquote 1ml in 1.5ml EP tube and stored in -20 freezer (3 weeks at least are absolutely fine)

Hope it helps.