The Analysis of Some Sulphonated Azo Dyes by Mixed Mode HPLC

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Abstract
A mixed mode (anion exchange/reverse phase) column for the analysis of some commercial sulphonated azo dyes was investigated as an alternative to simple reverse phase columns which require the use of either somewhat aggressive acidic elution solvents or the inclusion of ion pair reagents. Good separations of structural isomers were obtained using isocratic elution with solvents containing acetonitrile and near neutral phosphate buffers. A pattern of pH dependence for the retention times distinguished dyes according to the number of sulphonate groups present in their structure. Low levels of impurities in the commercial dyes could be observed by using a methanol/water solvent which did not elute the principal component.