Raman Spectral Analysis for Quality Determination of Grignard Reagent

Grignard reagent is one of the most popular materials in chemical and pharmaceutical
reaction processes, and requires high quality with minimal adulteration. In this study, Raman
spectroscopic technique was investigated for the rapid determination of toluene content, which
is one of the common adulterants in Grignard reagent. Raman spectroscopy is the most suitable
spectroscopic method to mitigate moisture and CO2 interference in the molecules of Grignard reagent.
Raman spectra for the mixtures of toluene and Grignard reagent with different concentrations
were analyzed with a partial least square regression (PLSR) method. The combination of spectral
wavebands in the prediction model was optimized with a variables selection method of variable
importance in projection (VIP). The results obtained from the VIP-based PLSR model showed the
reliable performance of Raman spectroscopy for predicting the toluene concentration present in
Grignard reagent with a correlation coefficient value of 0.97 and a standard error of prediction (SEP)
of 0.71%. The results showed that Raman spectroscopy combined with multivariate analysis could be
an effective analytical tool for rapid determination of the quality of Grignard reagent.
Keywords: Grignard reagent; chemical adulteration; Raman spectroscopy; variable importance in
projection; multivariate analysis; quality determination