[Assay of plasma xanthine and hypoxanthine by coupled gas chromatography-mass spectrometry and sampling problems].

The differential assay of xanthine and hypoxanthine in plasma, serum and erythrocytes was performed using a combination of GC and MS with chemical ionisation. The influence of sampling conditions was studied, in particular the latency period between the collection of the blood and the separation of the plasma and the cells, the nature of the anticoagulant used and the method of storage of the samples. Firstly, this study confirms that EDTA is the most appropriate anticoagulant. It also showed that an immediate deproteinisation is necessary after separation of the plasma and the cells, in order to prevent any "in vitro" modification of the oxypurines, in particular erythrocyte hypoxanthine.