A reproducible gas chromatographic mass spectrometric assay for low levels of methylphenidate and ritalinic acid in blood and urine

A rapid, sensitive method of analysis for methylphenidate and ritalinic acid in blood and urine has been developed using gas chromatography mass spectrometry and selected ion monitoring for separation and detection. The methylphenidate is isolated by solvent extraction into chloroform and the ritalinic acid is isolated by salting out into isopropyl alcohol, followed by methylation and subsequent solvent extraction. The method has been applied to the study of methylphenidate metabolism and excretion in adults and hyperactive children under‐going treatment with methylphenidate.