Abstract: GC was applied to the determination of related substances, i.e., 3,5-(trifluoro-dimethyl)-aceto-phenone, R and S-3,5-(trifluoro-dimethyl)-phenyl-ethanol, in reaction liquid of synthesis of R-3,5-(trifluoro-dimethyl) phenyl ethanol. Chiral capillary chromatographic column of cp-chirasil-Dex CB (25 m×0.25 mm, 0.25 μm) was used for separation with programmed temperature elevation from 100 ℃ to 140 ℃, and FID was used in the GC-analysis. p-Fluoroacetophenone was used as internal standard. Linear relationships between values of Ai/As and mass concentration of the 3 related substances were found in definite ranges, with detection limits (3S/N) in the range of 0.1-0.2 mg·L-1. Tests for recovery and precision were made, giving values of recovery in the ranges of 94.2%-104% and RSD′s (n=7) in the range of 2.1%-3.5%.