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

Retention index under the programmed temperature gas chromatography (PTGC) conditions (I^T) is widely accepted despite of its unsatisfactory reproducibility. Effects of heating rate (r_T), stationary liquid film thickness (d_f), inlet pressure (p_i), initial temperature (T_o) and polarity of stationary phase (s_p) on I^T reproducibility were studied in the present work. We found that excellent reproducibility and regularity of I^T values are obtainable at conditions of relatively low T_o and relatively high r_T and p_i, 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 T_o and relatively low r_T for thin-film columns). The I^T 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 I^T reproducibility.