Pallmann effect

When a constant ionic strength of the test solution is maintained and the reference electrode liquid bridge is filled with a solution of a salt whose cation and anion have similar mobilities (for example solutions of KCl, KNO3 and NH4NO3), the liquid-junction potential is reasonably constant (cf. p. 24-5). However, problems may be encountered in measurements on suspensions (for example in blood or in soil extracts). The potential difference measured in the suspension may be very different from that obtained in the supernatant or in the filtrate. This phenomenon is called the suspension (Pallmann) effect [110] The appearance of the Pallmann effect depends on the position of the reference electrode, but not on that of ISE [65] (i.e. there is a difference between the potentials obtained with the reference electrode in the suspension and in the supernatant). This effect has not been satisfactorily explained it may be caused by the formation of an anomalous liquid-junction or Donnan potential. It... 

The systems a and b are equivalent and measure the pH of the equilibrium liquid The systems c and d give an E M F which can be alternatively interpreted as the pH of the suspension or as the pH of the equilibrium liquid disfigured by sol concentration effect or Pallmann effect ... 

Loosjes could produce a change in E M F analogous to the sol concentration and the Pallmann effect by placing a liquid junction alternatively in a capillary and in a wide tube ... 

I 10. Potential measurements in colloidal systems Pallmann Effect, sol concentration EFFECT. 184... 

Suspension Effect A finite potential, the Donnan potential, may exist between a suspension and its equilibrium solution. Also referred to as the Pallmann or Wiegner effect. 

This effect has been described and extensively investigated by Pallmann and WiEGNER who determined the pH in suspensions of clays and similar materials De... 

Loosjes (/ c.) has worked this picture out in a very schematized way and deduced the following equation for the Pallmann and sol concentration effect... 

Other data of Pallmann, a series of experiments of Loosjes himself and the sol concentration effect by De Bruyn are equally. well described. 

---