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The main components of alkaline and acidic detergent solutions are strong electrolytes with a high degree of dissociation. If an electric field is applied in an aqueous system, the ions take over the current transport. This depends, among other things, on the concentration of the electrolyte. By measuring a defined value - the so-called specific conductivity - a linear dependency is given in the concentration range commonly used in cleaning practice and the concentration can be easily determined. The specific conductivity is specified in the unit Siemens or millisiemens per centimeter (S/cm; mS/cm).

Alkaline cleaning solutions, especially for automatic bottle cleaning, consist of sodium hydroxide and so-called active ingredient concentrates. Concentration losses caused by carryover or carbonization can be determined by determining the alkaline component in accordance with
T-740.01.041 Electrolytic conductivity of acidic and alkaline cleaning agents
T-741.02.032 Alkaline cleaning agents - sodium hydroxide only
T-741.03.032 Alkaline cleaning agents containing carbonate - sodium hydroxide and soda
T-741.04.023 Alkaline cleaning agents containing carbonate in the presence of phosphates and soiling - sodium hydroxide and soda
T-741.05.032 Alkaline cleaning agents containing aluminum - sodium hydroxide, aluminum
T-741.06.032 Alkaline cleaning agents containing aluminum - sodium hydroxide, aluminum, soda
can be controlled. However, the active ingredient concentrates are only recorded if it is ensured that the required concentration of the desired active ingredient has been added or dosed using appropriate dosing equipment (proportional dosing). If this is not the case, i.e. if the active ingredient concentrates are prepared and dosed manually, a separate check of the active ingredient concentration is advisable. The determination methods are very different and are specific to a particular active ingredient concentrate*. The method should be requested from the manufacturer.

* e.g. P 3-stabilon; Henkel Hygiene GmbH, D-40554 Düsseldorf, https://www.henkel.de/

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

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