The non-linear calibration in quantitative determinations by high performance thin-layer chromatography utilizing a fibre optic fluorescence detector is examined. Dansyl derivatives of polyamines, as model compounds, are separated in HPTLC silica-gel plates with chloroform:triethylamine (TEA):polyoxyethylene-10-lauryl ether (POLE) (8:4:5%) (v:v:m) as solvent. The obtained calibration graphs show a non-linear relationship between the fluorescence intensity and the quantity of the amine (0-150ng).