Double-hexyl-trifluoro-alkyl benzene is a common liquid crystal monomer used in the thin film transistor liquid crystal and the first grade tiny twisted nematic liquid crystal. During the manufacturing process

its defluorinated impurity will inevitably appear. Therefore

MS analysis of the monomer and its impurity is highly essential in controlling the fluoride-losing impurity

thus increasing purity of the liquid crystal monomer. By comparing the mass spectrums of n-hexyl 3

5-double loop-2-fluorophenyl and propyl bicyclo hexyl-3

4-difluorophenyl

it is discovered that there are significant differences between the abundance ratio

m/z

127 and 140 in the two mass spectra. The resonance forms of the two matials are compared

providing a reliable basis for the conform of the defluorinated impurities.