CHARGE-TRANSFER COMPLEXES OF BARBITURATES AND PHENYTOIN

Simple and sensitive spectrophotometric methods are described, for the first time, for the determination of sodium salts of phenobarbital (1 ), thiopental (2), methohexital (3) and phenytoin (4). The methods are based on the reaction of these drugs as n-electron donors with the si gma-acceptor iodine and various pi-acceptors: 7,7,8,8-tetracyanoquinod imethane; 2,3-dichloro-5,6-dicyano-1,4-benzoquinone; 2,3,5,6-tetrachlo ro-1,4-benzoquinone; 2,3,5,6-tetrafluoro-1,4-benzoquinone; 2,5-dichlor o-3,6-dihydroxy-1,4-benzoquinone; tetracyanoethylene and 2,4,7-trinitr o-9-fluorenon. Depending on the solvent polarity, different coloured c harge-transfer complexes and radicals were developed. Different variab les and parameters affecting the reactions were studied and optimized. The formed complexes were examined by UV/VIS, infrared and H-1-NMR. D ue to the rapid development of colours at ambient temperature, the obt ained results were used on thin layer chromatograms for the detection of the investigated compounds. Beer's plots were obeyed in a general c oncentration range of 1-400 mu g ml(-1) for the investigated compounds with different accepters. Interference from some co-formulated drugs was also studied. No interference was observed due to additives common ly present in the pharmaceutical preparations. The proposed methods co uld be applied successfully to the determination of the investigated c ompounds in pure and pharmaceutical dosage forms with good accuracy an d precision, the recoveries ranged from 98.7 +/- 0.5 to 101.1 +/- 0.5% . The results were compared favourably with the official methods. (C) 1997 Elsevier Science B.V.