All alkaline cleaning solutions or "stack solutions" that contain sodium hydroxide (NaOH) as well as dissolved aluminum and/or soda (Na2CO3) in addition to free chlorine.
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 concentration of alkaline cleaners in sodium hydroxide (NaOH) and soda (Na2CO3).
All alkaline cleaning solutions or "batch solutions" that contain soda (Na2CO3) as a cleaning component in addition to sodium hydroxide (NaOH).
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
Determination of the concentration of alkaline cleaners in sodium hydroxide (NaOH) and aluminum (Al).
All alkaline cleaning solutions or "stack solutions" that contain dissolved aluminum (Al3+) and/or soda (Na2CO3) in addition to sodium hydroxide (NaOH) as a cleaning component.
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.
Determination of the concentration of alkaline cleaners in sodium hydroxide (NaOH), soda (Na2CO3) and aluminum (Al).
All alkaline cleaning solutions or "stack solutions" that contain dissolved aluminum (Al3+) and/or soda (Na2CO3) in addition to sodium hydroxide (NaOH) as a cleaning component.
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.
Consideration of phosphates and impurities, especially hydrolysis products of proteins in the concentration determination of alkaline cleaners on sodium hydroxide (NaOH) and soda (Na2CO3).
All alkaline cleaning solutions or "batch solutions" that contain soda (Na2CO3) as a cleaning component in addition to sodium hydroxide (NaOH).
Additives containing phosphoric acid in particular - but also other types of additive - can simulate a more or less significant Na2CO3 content due to their buffering effect. Firstly, phosphoric acid significantly blunts the p-value by forming sodium phosphate (Na3PO4) and secondly, the difference between the m-value and the p-value is increased because sodium dihydrogen phosphate (NaH2PO4) is largely formed from disodium hydrogen phosphate (Na2HPO4) in the pH range 8.2 to 4.3. The same applies - but to a lesser extent due to the molecular sizes - to typical phosphonic acids or their salts, but not, for example, to most surfactants.
To determine the exact concentration or pH value, the content of buffering substances - phosphates and impurities - must be taken into account in addition to the degree of carbonation, as otherwise the concentration of the active cleaning agent will be too high.
Determination of the p-value 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 most important step is the expulsion of CO2. This is to ensure that no more hydrogen carbonates or carbonates can form during the subsequent back titration with NaOH. For this purpose, a significant acidification below pH 4.3 must be carried out with acid in order to be able to drive out CO2 using an inert gas.
The proportion of buffering substances can then be determined by back titration with NaOH to pH 4.3 or 8.2.