Flow Analysis with Cerium (IV) Colorimetric Reagent for Determination of Procaine and Elucidation of the Color Species by Computational Investigation

Abstract

Flow injection analysis (FIA) with spectrometric detection was applied to determine procaine hydrochloride (PR) based on the reaction of procaine and cerium (IV) sulfate tetrahydrate produced a red compound that be enhanced sensitivity by adding sodium dodecyl sulfate (SDS). A calibration graph was linear in the range of 1-150 mg L^-1 of PR with R² of 0.9998. The detection limit (3S/N) was 0.75 mg L^-1. Percentage recoveries and relative standard deviation were 100-108 and 2.9, respectively. To help elucidating the colored species, the density functional theory and the time-dependent density functional theory were used to calculate the relative energies and the absorption spectra of all possible complexes involved in the reaction. The calculation suggests that a Ce(IV) could initially form a complex with procaine at the carbonyl oxygen and cause ester hydrolysis leading to a more stable Ce(IV)/PABA complex in solution. The proposed method was applied to determine PR in pharmaceutical and cosmetic preparation and compared to USP 2004. At 95% confidence, there was no significant difference between the results of both methods. The method should provide an accessible and eco-friendly way to determine PR in a typical laboratory.