Search: Phosphat

Phosphate ions form a yellow color in the presence of the molybdovanadate reagent. The color is determined using a photometer.

Refer to W-000.28.111 Phosphate in Water, Reaction with Vanadate-Molybdate Reagent (Rapid Test)

Separation of bromide, chloride, fluoride, nitrate, nitrite, oxalate, phosphate and sulfate through ion chromatography followed by conductivity detection

The anions chloride, sulfate, nitrate and phosphate are separated by means of ion chromatography. The conductivity detection with a suppressor provides quantitative information about the anions. The concentrations are calculated by means of the individual areas under the peaks from the chromatogram with reference to calibration factors.

Separation using ion chromatography and subsequent conductivity detection (of other anions as well)

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.