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Alkaline cleaning agents and disinfectants containing chlorine can be determined by their alkalinity concentration. The chlorine present destroys most indicators by oxidation. Before adding the indicator, the chlorine must be eliminated by adding sodium thiosulphate to the sample.

Determination of the quicklime (CaO) or sodium hydroxide (NaOH) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding equivalent concentration (normality) up to the color change of phenolphthalein (pH 8.2).

Quicklime

Sodium hydroxide

If the alkaline solution is likely to be strongly influenced by carbonic acid or if the cleaning solutions are used over a longer period of time ('batch cleaning'), the degree of carbonation must be taken into account to determine the exact concentration or pH value, as the resulting soda has a greatly reduced cleaning effect, but simulates an excessively high concentration of the active cleaning agent.

Determine the sodium hydroxide (NaOH) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding normality up to the color change of phenolphthalein (pH 8.2).

   NaOH + HCl           →         NaCl      +   H₂O             colorless against phenolphthalein

2 NaOH + H₂SO₄      →         Na₂SO₄ + 2 H₂O

Determination of the soda ash (Na₂CO₃) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding normality up to the color change from methyl orange (pH 4.3).

   Na₂CO₃  + HCl        →       NaHCO₃  + NaCl

   NaHCO₃  + HCl        →      NaCl      + H₂O + CO₂    yellowish brown against methyl orange

2 Na₂CO₃   + H₂SO₄   →   2 NaHCO₃ + Na₂SO₄

2 NaHCO₃  + H₂SO₄    →  2 Na₂SO₄ + H₂O + 2 CO₂

The sodium hydroxide bound as aluminate and titrated in the p-value determination is calculated by subsequent determination of the aluminum and deducted, as it is no longer available for purification.

The aluminum determination itself is based on the reaction between aluminum hydroxide and sodium fluoride, in which sodium hydroxide is released and thus serves as a measure for calculating the aluminum.

Carbonates interfering with the titration are precipitated with Ba²⁺ ions.

The sodium hydroxide bound as aluminate and titrated in the p-value determination is calculated by subsequent determination of the aluminum and deducted, as it is no longer available for purification.

The aluminum determination itself is based on the reaction between aluminum hydroxide and sodium fluoride, in which sodium hydroxide is released and thus serves as a measure for calculating the aluminum.

Titration against methyl orange instead of the Tashiro indicator leads to incorrect results. When sodium fluorif (NaF) is added to the alkaline solution, hydrofluoric acid (HF) is formed. The hydrofluoric acid destroys the methyl orange indicator.

The same principle applies here as for determining the concentration of alkaline cleaning solutions, except that titration solutions of corresponding normality are used.

Since the titration here is performed from the acid side (and not from the alkali side as in the determination of the p-value for alkaline detergents), the "minus p-value" (-p-value) is determined for acidic detergents.

  H⁺ +  NaOH     →  H₂O  +  Na⁺     very slightly pink against phenolphthalein