Lack of in-situ instrumentations made difficult to monitor concentration level of various ions in site for specific management of environmental and agricultural practices. A new fast response and low sample volume soil solution collected in stainless steel solution sampler combining with ion selective electrode (ISE) or Fiber-optic wire probe has been developed to determine in-situ ion concentrations in soil solution. However, the ion exchange between stainless steel sampler and surrounding soil solution is dominated by diffusion process. The concentration of ions diffused into stainless steel solution sampler with time needs to be estimated for establishing accurate monitoring schedule. To accomplish such task, a simplified model to predict the time-varying nitrate concentrations in the inner cup can be developed by using simple electric circuit analogies. The slope of the relative concentration inside the stainless steel cup to overall average ion concentration in equilibrium gives overall resistance to ion diffusion. Employing overall resistance, the sensitivity of diffusion on the properties of sampler cup will be investigated. Moreover, this paper describes the relationships between overall resistance and the mass diffusion coefficient of examined ions using simplified analytical model.