Determination of hydrofluoric acid, ammonium fluoride, and maleic acid in acid cleaning solutions

A direct thermometric titration (TET) with 2 mol/L NaOH is used to determine the HF, NH₄F, and maleic acid (C₄H₄O₄) contents of acid cleaning solutions. Three endpoints (EPs) are obtained, which may be assigned as follows:

EP1: C₄H₄O₄ (pKa1 = 1.9), HF (pKa = 3.17)
EP2: C₄H₄O₄ (pKa2 = 6.07)
EP2: NH₄F (pKa = 8.2)

The HF content is determined by subtracting the difference (EP2-EP1) from EP1.

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