Phenylacetone was chromatographed on alumina with mixture of toluene and 1,4-dioxane as a mobile phase in a thin-layer chromatography (TLC) system. All the chromatograms were scanned with a densitometer. It was found that for such a binary mobile phase, there is a range of stronger component concentration that gives both peaks of Gaussian shape and triangle-like shape as well. Non-Gaussian peaks of phenylacetone chromatographed on alumina with a mixture of toluene and 1,4-dioxane were observed in the case of relatively low concentration of the latter in the mobile phase. Appropriate model describing the observed retention process is suggested.