[Determination of plasma theophylline in the newborn by high resolution gas chromatography and specific detection (author's transl)].

The authors describe a micromethod for the determination of blood concentration of theophylline in premature newborn infants. The method includes the specificity of separation in gas phase chromatography on a glass capillary column, and the sensitivity of thermo-ionic detection. After addition of isobutyl-3-methyl-1-xanthine, which constitutes an internal standard, extraction is performed in acid pH, with the mixture dichloromethane-isopropanol. The derivation consists of an N-pentyl reaction. Analysis was carried out on a glass capillary column SE-30 measuring 75 m x 0.5 mm. The technic used is simple and rapid. Its application in pediatrics has been particularly studied; the limit of quantitative detection was 0.1 mg/l. The plasma sample may be 0.05 ml. The reproducibility is about 2% in usual therapeutic doses. The specificity of the method has been widely debated, in particular the stages of extraction, derivation, separation and detection. The authors are convinced that the analyses requiring systems of specific detection, more and more widely used, require a chromatographic apparatus with a high power of resolution; this is illustrated by an example.