Turbidimetry
In turbidimetry (not to be confused with nephelometry ) the transmission or penetrating light intensity through a suspension of the precipitate is measured during a titration. In contrast to photometry , turbidimetry does not measure absorption. An ideal example would be the reaction of Ba 2+ with SO 4 2− to form BaSO 4 . The reaction mixture becomes more and more cloudy up to the equivalence point. In the cloudy solution, the light is mainly scattered and not absorbed. After the equivalence point, the turbidity (and thus the light scattering) no longer changes, since no further precipitate is formed. Since the scattering depends on the particle size, the reaction must be carried out in a very reproducible manner in order to obtain precise results. A mixture of glycerine and alcohol serves to stabilize the particles and prevents the solids from settling quickly.
Turbidimetric and nephelometric titrations are not very precise as the end point determination depends on the particle size, which is not really reproducible. However, the sensitivity is very good; in the above example, sulphate can still be determined in the ppm range .
Individual evidence
- ↑ Entry on turbidity measurement. In: Römpp Online . Georg Thieme Verlag, accessed on June 13, 2014.
- ↑ Entry on turbidimetry in Flexikon , a wiki from DocCheck , accessed on June 25, 2014.
- ^ Daniel C. Harris, Textbook of Quantitative Analysis 1998