RP TLC of some newly synthesized azo-dye derivatives

Abstract

The chromatographic behavior of series of azo-dye derivatives has been studied by RP C 18 TLC with water-methanol, water-acetone, water-dioxane, and water-acetonitrile mobile phases. The mechanism of retention was investigated and the retention constants, R M 0 , were determined by extrapolation. Correlations between retention constants, R M 0 , and lipophilicity, C 0 ( C 0 = R M 0 /m) and log P (ACD log P ) were investigated. Better correlations were obtained between C 0 and log P than between R M 0 and log P . These C 0 values may be use as a measure of the lipophilicity of the compounds investigated.The effect of mobile phase pH on retention of azo-dye derivatives was studied in RP C 18 TLC with diluted acetic acid-methanol, 20 + 30 ( v/v ) as mobile phase. Different methods were used to measure mobile phase pH. p K a values were determined on the basis of the relationships between analyte retention and mobile phase pH. Because the investigated azo dyes are newly synthesized compounds these p K a value...