Micromethod for the determination of bupivacaine in maternal and foetal blood during obstetric analgesia

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Abstract
A method for the determination of bupivacaine in maternal and foetal blood during obstetric analgesia is described. The drug and the internal standard, 1-pentyl-2-(2,6-xylylcarbamoyl)-piperidine, are initially extracted into methylene chloride. Perchloric acid is added to retain bupivacaine and the standard as Perchlorates in the organic phase accomplishing a selective separation from less hydrophobic amines. Bupivacaine and the standard are then re-extracted into sulphuric acid, followed by a purification with methylene chloride. The aqueous extract is finally made alkaline and the compounds extracted into 10 μl methylene chloride. This extract is analysed by gas chromatography using a 3% OV-17 column. The standard deviation of the method at therapeutic concentrations is about 10% and the lowest level which can be determined with reasonable accuracy is 15 ng ml−1.