Intercalates of organics with montmorillonites (MMT) are perspective sorbents for scavenging organic pollutants (chlorophenols, dioxines) from water environment. Easily exchangeable interlayer cations in MMT can be replaced by organoammonium or organophosphonium cations. A simple and fast isotachophoretic method for determination of tetramethyl- (TMA⁺), trimethyl(phenyl)- (TMPA⁺), and tetrabutylammonium (TBA⁺) cations in water solution based on MMT intercalation was proposed and verified. The tested method yielded reproducible and correct data. The achieved detection limits and sensitivity match the requirements of the batch equilibrium technique used for adsorption experiments. Sorption curves showed the following sorption maxima for the cations per g of Na-MMT: 0.98 mmol TMA⁺, 0.97 mmol TMPA⁺, and 0.84 mmol TBA⁺. These values are in a very good agreement with elemental analyses of saturated TMA-MMT, TMPA-MMT and TBA-MMT.