How can a half drop of naoh solution be added from the buret?

Hello!

It's actually easy to add a half drop of NaOH from the buret, you'll only need to be careful.

For doing that, you'll need to first open the flow of the buret until a little drop appears, and close it before it falls to the titrating flask. Then, you'll need to rinse the tip of the buret with deionized water to make the half drop fall into the titrating flask. 

Don't worry about diluting your sample with the deionized water, since you are titrating the total moles of your analyte in the solution, and those won't change with concentration.

Have a nice day!