The recommended concentration of acidulated phosphate (APF) fluoride gel is:

An aqueous solution of acidulated phosphate fluoride is prepared by dissolving 20 grams of sodium fluoride in 1 liter of 0.1 M phosphoric acid and to this is added 50% hydrofluoric acid to adjust the pH at 3.0 and fluoride ion concentration at 1.23%. It is also called as Brudevold's solution. Essentials of preventive and community dentistry Soben Peter 5th edition page no. 258