摘要：RPTLC and optimizing mobile phase methods in Rm value determination as one of lipophylicity parameters in drug design Background: The early process to successfully achieve its target is drug penetration or absorption. Of the three physicochemical parameters i.e, lipophyllicity, electronic and steric parameters, the lipophyllicity parameter is the most reponsible in drug absorption process. The research was aimed to determine retention modified (Rm) value of barbituric acid compound derivatives using RPTLC metod and mobile phase optimizing. Methods: This study was conducted on barbituric acid compound derivatives by using reverse phase thin layer chromatography (RPTLC). Silica Gel GF 254 that had been submerget in the mixture of liquid paraffin and petroleum eter (95:5) was used as a stationary phase. The mixture of polar to non polar solvent was used as mobile phase. Results: Research showed that in this method the most optimum of mobile phase was indicated by methanol and acetic acid mixture in the ratio of (1:9). The resulted Rm values of 5,5-diethylbarbituric acid, 5,5-diallylbarbituric acid, 5-allyl-5-isopropylbarbituric acid, 5-allyl-5-isobuthylbarbituric acid, 5-etil-5-(1-methylbutyl) barbituric acid, 5-(1-cyclohexene-1-yl)-1,5-dimethylbarbituric acid and 5-ethyl-5-phenylbarbituric acid were as follow 0.116; 0.144; 0.162; 0.221; 0.262; 0.187 and 0.199. Conclusions: The most optimum mobile phase in this method was the mixed solvents that had lower polarity, i.e, the mix of methanol and acetic acid in the ratio of (1:9). The H1 , H2 and H3 substituens in barbituric acid nuclei showed, the longer carbon chain, the higher the Rm values, howover the existing of double bond in such substituents will decrease the Rm value. Keywords: RPTLC, mobile phase, Rm value ABSTRAK Latar belakang: Proses awal keberhasilan obat dalam mencapai target adalah penetrasi atau absorpsi. Parameter lipofilisitas paling bertanggung jawab terhadap proses absorpsi obat dibanding parameter elektronik dan stearik. Tujuan penelitian ini adalah penggunaan metode RPTLC dan optimasi fase gerak dalam penentuan harga retention modified (Rm) senyawa turunan asam barbiturat. Metode: Penelitian dilakukan terhadap senyawa turunan asam barbiturat, dengan metoda kromatografi lapis tipis fase terbalik. Digunakan fase diam silika gel GF 254 yang telah dibacem dengan campuran parafin cair dan petroleum eter dengan perbandingan (95:5). Fase gerak yang digunakan dipilih campuran pelarut dari yang sangat polar sampai yang kurang polar. Hasil: Fase gerak yang paling optimum digunakan dalam metode ini adalah campuran metanol dan asam asetat dengan perbandingan (1:9). Harga Rm yang diperoleh secara berturutan, asam 5,5-dietilbarbiturat, asam 5,5-dialilbarbiturat, asam 5-alil-5- isopropilbarbiturat, asam 5-alil-5-isobutilbarbiturat, asam 5-etil-5-(1-metilbutil) barbiturat, asam 5-(1-sikloheksen-1-il) 1,5- dimetilbarbiturat dan asam 5-etil-5-fenilbarbiturat adalah: 0,116; 0,144; 0,162; 0,221; 0,262; 0,187 dan 0,199. Simpulan: Fase gerak yang paling optimum dalam metoda ini adalah bukan fase berair, tetapi berupa campuran pelarut yang mempunyai polaritas rendah, yakni campuran metanol dan asam asetat dengan perbandingan (1:9). Substituen atom H1 , H2 dan H3 pada inti asam barbiturat, menunjukkan makin panjang rantai karbon, makin tinggi harga Rm-nya. Adanya ikatan rangkap pada substituen menurunkan harga Rmnya.
