I'm looking for a theory to calculate the electrical conductivity of electrolytes, namely $\ce{NaCl}$ and tartaric acid ($\ce{C4H6O6}$) dissolved in water, depending on their concentration.
The only equation I could find was the one derived from the Debye-Hückel theory, which I read works great for 1:1 electrolytes like $\ce{NaCl}$ (not sure about tartaric acid 1:2 electrolyte), but only until about 0.1 M.
The concentrations in my case vary from 0.2 M up to 4.0 M.
Is there a theory I can use to calculate conductivities in that range, or is the Debye-Hückel theory the only one?
