Thin layer chromatography barbiturates

The utility of the highly soluble 6-cyclodextrin derivatives (soluble polymer and dimethyl-6-cyclodextrin) in RPTLC is illustrated in the separation of barbiturates. The lipophilicity of a barbiturate or any guest decreases when included in a cyclodextrin-cavity. Therefore its mobility is modified in reversed phase thin layer chromatography. With this simple and rapid method, the stability of a complex can be estimated empirically (Table II). The "b" value of the following equation is characteristic for the complex stability (in water ethanol =4 1 solution, R determined at 5 different cyclodextrin concentrations for 21 barbiturates) ... 

The sorption efficiency of MC was determined as the ratio of the quantity of the adsorbed substance to its initial amount (w / w), expressed in % for a certain ratio (w / w) of adsorbent to substance. Optimal ratios of adsorbent to substance equal 15-20 for barbiturates, 20 - 25 for cyanocobalamin and bilirubin, and 40 - 50 for hemoglobin. The initial concentration of absorbed substances was 100 - 200 pg/ml. The substances were incubated for lmin with MC either in physiological solution or in donor plasma and donor blood at room temperature (pH 7.4). The concentration of substances in the solutions was measured by differential visual and UV-spectroscopy. Concentrations of substances in blood and plasma and adsorption of total plasma proteins was determined by thin-layer chromatography with a fluorescent label. 

The method does not distinguish between the common 5,5-substituted barbiturates. If the physician proposes to institute a forced alkaline diuresis or haemodialysis, it is essential to confirm the presence of a long-acting barbiturate (e.g, barbitone, phenobarbitone) by thin-layer chromatog-raphy or gas chromatography. 

Heaton, A.M., and Blumberg, A.G. (1969) Thin-layer chromatographic detection of barbiturates, narcotics, and amphetamines in urine of patients receiving psychotropic drugs. Journal of Chromatography, 41,367-370. Ono, M., and Engelke, B.F. (1969) Procedures for assured identification of morphine, dihydromorphinone, codeine, norcodeine, methadone, quinine, methamphetamine, etc., in human urine. Bulletin in Narcotics, 21, 31-40. 

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