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Evaluation of Dimethylformamide (DMF) as an Organic Modifier in Hydrophobicity Index (Rm) Determination Olakunle S Idowu, Adedigbo A Fasanmade and Ajibola A Olaniyi Abstract Purpose: Ideal behaviour of mixtures of organic modifier and water is reflected by a linear relationship between refractive index and fraction of organic modifier in the mixture. This study was carried out to investigate dimethylformamide (DMF) as an organic modifier in hydrophobicity index (Rm) determination. Method: We quantitatively evaluated the problem of partial miscibility of phases associated with the reversed phase thin layer chromatographic (RPTLC) system, using liquid paraffin as stationary phase and acetone/water mixtures as mobile phase. Ideality of behaviour of acetone/water mixtures was investigated by refractive index measurements. Rm values of compounds were determined using mixtures of acetone and water as mobile phase. Results: DMF/water mixture behaved ideally across the whole concentration range investigated (0-100%) while acetone/water mixture deviated from ideal behaviour when the concentration of acetone in the mixture was 80%. DMF also gave a better extrapolation of Rm value from linear regression of partition data than acetone for bezafibrate used as a test-drug molecule. Conclusion: DMF is a better organic modifier than acetone in this RPTLC system. These findings could be extended to drug-receptor and drug design studies. The use of dimethylformamide (DMF) in preference to acetone as organic modifier is proposed in this study. Keywords Drug design dimethylformamide, hydrophobicity index, organic modifiers

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