Water and Body Liquids

The addition of electrolytes such as NaCl or KCl lowers the permittivity proportionally to concentration (e.g., with a dielectric decrement, Acr, of 4 for a 250 mmol/L concentration of KCl cf. Section 3.1.1). 

The high permittivity is one reason for the dissociative power of water. Ionic bonds are split up so that ions exist in aqueous solutions in a free but hydrated form. Because of the strong dipolar electric field, water molecules are attracted to ions and local charges. 

Ice has a static relative permittivity of approximately 92 at 0 °C (at low frequencies, but fallen to 10 already at 20 kHz), slightly anisotropic ( 14%), and increasing with lower temperature. The characteristic frequency of the relaxation is much lower than for water, approximately 3 kHz, and with disturbing conductive effects at less than 500 Hz (Hasted, 1973). 

The living cell must contain and be surrounded by aqueous electrolytes. In human blood, the most important cations are H, Na, K, Ca , and Mg +, and the most important anions are HCOf, CP, protein , HPO4, and SO4 . Note that protein in the blood is considered as a negative (macro)-ion. 

The intracellular and extracellular electrolytes are listed in Table 2.6. They cause an electrolytic conductivity on the order of 1 S/m. Up to at least 10 MHz, it is considered to be frequency independent (Cooper, 1946). 

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