The official methods1 for the determination of isoprenaline sulphate and methyldopa are based on measurement of the colour produced when these compounds are treated with iron salts in the presence of an alkaline buffer. Other spectrophotometric methods based on the use of sodium molybdate,2 4-nitrobenzenediazonium c h l ~r i d e , ~ thiosemicarbazide4J and sodium hexanitritocobaltate(III)6 have also been reported.Feigl ' and Feigl et aZ. 8 reported that chloranil (tetrachloroquinone) forms coloured condensation products with primary and secondary aryl amines, amino acids, phenols and naphthalene. Birks and Slifking reported that some amino acids form n -T charge-transfer complexes with chloranil in aqueous ethanol (50% V / V ) buffered at certain pH values. Al-Sulimany and Townshendl0 described a procedure for the determination of various amino acids using chloranil. Recently, Al-Ghabsha et aZ.ll investigated the reaction of chloranil with a wide range of arnines and described a method for their determination.This paper deals with the use of chloranil for the spectrophotometric determination of isoprenaline sulphate and methyldopa.
Experimental ApparatusBeckman double-beam spectrophotometer, Model 24.
ReagentsChZoraniZ soZutiort. Bufer solution, pH 9. A 0.05 M solution of d.isodium tetraborate.Prepared drug solution. Dissolve 20 mg of methyldopa or isoprenaline sulphate in 20 ml of 0.1 M hydrochloric acid. Neutralise with 0.05 M disodium tetraborate solution to pH 7 and dilute to 100 ml with water in a calibrated flask.A saturated solution of clhloranil in ethanol.
Keywords ; Acidic drug determination ; ion-pairing reagent ; basic fuchsin reagent ; spectrophotornetryThe basic dyes reported in the literature that could form salts with acidic compounds soluble in certain organic solvents are methylene b l ~e , l -~ rhodamine 6ZH,5 astrophloxim FF extra,596 safranin T,7 crystal violet ,as9 cationic red violet6310 and cationic blue 3.690 Basic fuchsin has been used for the determination of some surface-active agents.ll The underlying principle of the basic-dye technique for the determination of acidic compounds is that at a certain pH, the anion of the acidic compound, A-, reacts quantitatively with the basic dye cation, Bf, to form AB, which can be extracted by a suitable organic solvent. The choice of the solvent and pH is a compromise between minimum blank reading and quantitative extraction of AB. TschoegP2 described AB as a complex between the anionic drug and the cationic dye.However, Mukerjee and M y ~e l s 1 ~~~~ showed that the reaction is a simple salt formation. This paper deals with the use of basic fuchsin for determining picric acid, saccharin, phenylbutazone and probenecid.1967, 14, 6220.
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