**1. Introduction**

The basic electrolytic experiment consists of a homogeneous1 electrolytic solution with two identical electrodes (Fig 1). We know that a homogeneous solution hasn't boundaries or membranes, except the electrodes and the solution receipt.

**Figure 1.** The basic electrolytic experiment

Electrolyte solution selected as the most important of the human body: NaCl aqueous solution with a concentration of 0.9% by weight [i ].

<sup>1</sup> If NaCl is dissolved in water then NaCl is the solute (and the electrolyte), and water is the solvent, together form the solution

© 2012 Rodarte Dávila et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In a homogeneous conductive material the impedance (Z) is proportional to its length and inversely proportional to its cross sectional area (A) (Fig. 2).

**Figure 2.** The impedance (Z) of homogeneous conductive material is directly proportional to its length and resistivity and inversely with its area

$$\mathbf{Z} \mathbf{\overline{q}L/A} \mathbf{\overline{w}QL^2/V} \tag{1}$$

According with the Figure 2 Z=impedance, L=length, A=area, V=volume ρ=resistivity=1/σ (conductivity). An empirical relationship can be established between the ratio (L2 / V) and the impedance of the saline solution which contains electrolytes that conduct electricity through the sample. Therefore impedance (Z) = L / A = L2 / V.

Hoffer et al. [2] and Nyboer [3] were the first to introduce the technique of four surface electrodes Bio-impedance analysis.

A disadvantage presented by this technique is the use of a high current (800 mA) and a high voltage to decrease the volatility of injected current associated with skin impedance (10 000 Ω/cm2)[4]

Harris et al.[5], (1987) uses a four terminals device to measure impedance for the purpose of eliminating the effect of electrodes in an aqueous medium.

Asami et al.[6] , (1999) used a pair of coils submerged for monitoring the current induced in the coil pair, which he called electrode-less method, however still requires physical connections between the coils and electronic instruments.

To measure the complex spectrum of the permittivity of a biological culture solution Ong et al.[7], uses a remote sensor resonant circuit, to obtain the impedance of the environment by observing the resonant frequency and the frequency of zero reactance.

In another case for monitoring the fermentation process Hofmann et al.[8], Use a sensor based on a transceiver, as a way of overcoming the effect of having two metal electrodes to measure the impedance of the culture broth in a fermentation process, as in such processes the behavior of living cells is as small capacitors, then measure the impedance represented by these small capacitors correlates with the number and size of living cells in the system (Hofmann et al., 2005).
