Electrochemical signals can be obtained without obstacle of solution resistance when solution contains indifferent electrolytes. But, recently, some novel electrochemical technologies prefer salt free or hypohaline cell. In which exemplified by: salt free electrolysis, electric double layer capacitor etc. Unfortunately, electrochemical behavior at low ionic concentration is difficult to be observed because current-voltages are complicated by solution resistance. The difficulty is predicted to be overcome by use of large multi-charged ions such as polyoxometalate and ionic polymers during amplification effect of ionic strength. The effective amplification of the conductivity is extended to measurements of electric double layer capacitance at extremely low ionic concentrations. The observed capacitance is composed of the Helmholtz layer capacitance, CH, and the diffuse layer capacitance, CD, in a series connection, in which the observed capacitance is determined by the smaller of CH or CD. Use of PSS allows us to evaluate CD although CH is predominant to CD in conventional measurements. So we can discuss the composition of electric double layer at diffusion layer farther.