What function does after hydrogen phosphate in next preparation and is diNa or monoNa meant? NaF 150mg sodium hydrogen phosphate 750mg citric acid 525mg benzoeic 75mg

I think this is a classic requirement. However, I have to say that the NaF concentration is to the low end. I have here for me two formulas with 600 mg NaF/300 ml; One at pH = 6 and the other pH = 4. Also all other quantities are a quarter of the quantities from my formula. After multiplying with four I get the composition with a pH = 4.
is then immediately explained the role of after hydrogen phosphate. You should use the mono after salt with 2 aq.