Azo dyes, preparation and purification

Various liquid chromatographic techniques have been frequently employed for the purification of commercial dyes for theoretical studies or for the exact determination of their toxicity and environmental pollution capacity. Thus, several sulphonated azo dyes were purified by using reversed-phase preparative HPLC. The chemical strctures, colour index names and numbers, and molecular masses of the sulphonated azo dyes included in the experiments are listed in Fig. 3.114. In order to determine the non-sulphonated azo dyes impurities, commercial dye samples were extracted with hexane, chloroform and ethyl acetate. Colourization of the organic phase indicated impurities. TLC carried out on silica and ODS stationary phases was also applied to control impurities. Mobile phases were composed of methanol, chloroform, acetone, ACN, 2-propanol, water and 0.1 M sodium sulphate depending on the type of stationary phase. Two ODS columns were employed for the analytical separation of dyes. The parameters of the columns were 150 X 3.9 mm i.d. particle size 4 /jm and 250 X 4.6 mm i.d. particle size 5 //m. Mobile phases consisted of methanol and 0.05 M aqueous ammonium acetate in various volume ratios. The flow rate was 0.9 ml/min and dyes were detected at 254 nm. Preparative separations were carried out in an ODS column (250 X 21.2 mm i.d.) using a flow rate of 13.5 ml/min. The composition of the mobile phases employed for the analytical and preparative separation of dyes is compiled in Table 3.33. 

It was further found that the methods separate well the dyes and impurities, as demonstrated on the preparative chromatographic profile of Reactive orange 16 in Fig. 3.115. It was concluded from the results that the method can be used in the future for the purification and analysis of a wide variety of sulphonated azo dyes [171],... 

M. Chen, D. Moir, F.M. Benoit and C. Kubwabo, Purification and identification of several sulphonated azo dyes using reversed-phase preparative high-performance liquid chromatography. J. Chromatogr.A, 825 (1998) 37-44. 

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