Identification of barbiturates from their infra-red spectra

Abstract

A standardised technique has been. developed for preparing potassium bromide discs of barbituric acids for infra-red analysis, and the spectra obtained do not depend on the methods used for purifying and preparing the samples. The technique is suitable for identifying toxicological samples, as only small amounts are needed. BECAUSE of the importance of barbiturate drugs in medical and toxicological work, numerous physical methods of identification have been examined.l Infra-red absorption and X-ray diffraction techniques have been the most promising, as both methods give many possible points of identification, varying in relative intensities, by which a compound can be distinguished. Both methods suffer from the disadvantages that they are sensitive to barbiturate

Infrared identification of barbiturates with particular reference to the occurrence of polymorphism

“…, 1952) but, owing to the limited solubility of many of the barbituric acids, the spectra obtained were of low intensity and not always clearly distinguishable from each other. In an attempt to overcome the effects of polymorphism on solid phase spectra, Cleverley (1960) used a technique in which the substance, incorporated into a potassium bromide disc, was heated in an oven at about 10" above its melting point, then cooled and the spectrum recorded. This method suffers from the disadvantages that each compound has to be heated to a different temperature (melting points quoted by Cleverley range between 86" and 229"), and that many of the spectra obtained correspond to the amorphous forms of the substances, which again are not always distinguishable from each other (e.g.…”

Analytical chemistry

“…The determination of benzaldehyde in presence of aromatic ketones, and of mixtures of nitrobenzaldehydes, has been carried out ,725 and octylphenoxyethanol additives t o petroleum have been measured.726 Methods of sample preparation are described which give spectra of barbiturates unaffected by the initial crystalline state of the sample. 727 The applications of the longer-wavelengths absorption methods, microwave spectroscopy, nuclear magnetic resonance, and electron spin resonance to analytical problems are still very restricted by specialisation of apparatus and techniques. They will be considered in a future Report.…”