The effect of a non‐swelling (toluene) and a swelling (ethylene glycol (EG)) solvent on the grafting of an organophilic silane (octyltriethoxisilane) onto a smectitic clay was investigated. XRD patterns of the resulting materials reveals that the grafting occurred exclusively on the edges of the clay particles without intercalation, as evidenced by the non‐variability of the d‐value before and after the grafting. FTIR and TGA characterizations show that higher amount of silane was grafted when toluene was used as solvent. With EG, the clay particles were well‐dispersed and the grafting well controlled. These functionalized materials were used as carbon paste electrode modifiers to evaluate their abilities for electrochemical detection of organophilic pollutants at trace level. Carbendazim (cbz), a widely used fungicide was used as model compound. The clay functionalized in EG was the most efficient modifier, due to the combined effect of the characteristics of the pristine clay and the grafted silane. The electroanalysis experimental parameters were carefully optimized (pH 6.8, 15 min of accumulation time and 10 % of the modifier in the carbon paste). By varying cbz concentration, a 0.03 μM detection limit was obtained. The sensor provide very reproducible response but strongly affected by some metal ions interferences. By varying cbz concentration in river water, used as environmental sample model, higher detection limit was obtained (0.2 μM), due to interfering species.