Hello Jiangtao Xing

The retention index can be easily found in commercial MS databases such as NIST or Wiley as additional information to the spectrum. It is not given there for all stored spectra, but it is available for many entries.

Otherwise you can calculate the index yourself by taking the number C X 100, for functional groups you can pick the increment for this particular structure from the database of a single substituted compound and calculate the index given there minus the C number times 100. This way you get the indices for almost every functional group and from this you can just as easily calculate any index.

Good luck and best regards

Joachim Horst

Several free software options for predicting gas chromatographic retention indices include

1-DeepReI:which uses deep learning for accurate predictions.

2-Mordred: an R package for molecular descriptor calculations.

3-ChemmineR: can also be adapted for retention index predictions through machine learning.

4-ACD/Labs offers trial versions of their software for users seeking advanced features.