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.

Retention index under the programmed temperature gas chromatography (PTGC) conditions (IT) is widely accepted despite of its unsatisfactory reproducibility. Effects of heating rate (rT), stationary liquid film thickness (df), inlet pressure (pi), initial temperature (To) and polarity of stationary phase (sp) on IT reproducibility were studied in the present work. We found that excellent reproducibility and regularity of IT values are obtainable at conditions of relatively low To and relatively high rT and pi, as well as use of quality thick-film column under an operation in a single-retention behavior region (i.e., cubic equation model region). Most solutes were eluted in the dual-retention behavior region under the commonly used conditions described in the literature (i.e., relatively high To and relatively low rT for thin-film columns). The IT reproducibility under the optimum condition was approximately 37 times better than that under the commonly used conditions. The present work further validated the concept about dual- and single-retention behaviors of solutes in PTGC and proposed a principle to improve IT reproducibility.