A conventional library search neglects retention parameters, and the process includes only comparison of spectra. Some chemical components such as isomers have similar spectra, which may confuse chemists, but show chromatographic peaks at deferent retention times. The combined use of retention indices when searching libraries makes identification easier and more reliable. To perform this search, spectral libraries with retention indices are required. Using the same column and same analysis method described in the library is recommended to get good results