Gas chromatographic (GC) analysis and high-performance liquid chromatographic (HPLC) analysis of reaction mixtures of phenol hydroxylation on an alpha-Fe2O3 model catalyst are compared. The over-estimated phenol conversion, para-benzoquinone yield and olp selectivity derived from the GC results are caused by the oxidation reactions of phenol and its hydroxylation products with hydrogen peroxide at elevated temperature in the GC system. In the GC system hydroquinone can be oxidized by a trace amount of O-2 in the N-2 carrier gas, so even in the absence of residual hydrogen peroxide the para-benzoquinone yield and olp selectivity obtained might be higher than the real values. Cyclohexane, cyclohexanol and cyclohexanone are less reactive towards hydrogen peroxide at elevated temperature, so the influence of residual hydrogen peroxide on the reaction testing of cyclohexane oxidation by GC is not significant. (C) 2002 Elsevier Science B.V. All rights reserved.