Evaluation of sources of irreproducibility of retention indices under programmed temperature gas chromatography conditions.

•The mathematic difference method was used to study PTGC retention index (IT).•This study described suitable conditions to obtain reproducible IT.•Studies parameters included heating rate (rT), stationary liquid film thickness (df), inlet pressure (pi), initial temperature (To) and polarity of stationary phase (sp).•IT varied minimal when rT, df and pi are chosen at a greater value.