Alizarin Red S as a colored agent for the extraction--photometric and color measurement determination of some local anesthetic organic compounds

The possibility has been considered for using 1,2-dihydroxyantraquinonone-3-sulfoacid (Alizarin Red S, ARS) as a colored agent for the determination of organic bases as of their ion associates. Spectrophotometric and colorimetric properties of the ion associates of cetyltrimethylammonium bromide and local anesthetics Novocaine and Lidocaine with ARS have been studied in aqueous solutions at pH 2-6; the optimal conditions for the formation of ion associates have been determined and the extraction mechanism has been revealed. Calibration curve equations have been obtained for the dependences of the absorbance of extracts and back extracts of organic bases in aqueous and organic phases, as well as the chromaticity functions (CF) of the ion associates on the concentration of the organic bases in aqueous and organic phases. Molar absorption coefficients and CF of the considered ion associates have been determined. The advantages of the color measurement over spectrophotometry for the determination of molar absorption coefficients and CF have been demonstrated. An application of the developed procedure has been proposed. DOI: 10.1134/S1061934810090054
Optical methods based on the absorbance dependence on the pH of the solutions are widely used for studies of equilibriums in solutions, since they provide maximum information on the behavior [...]