A safer methylation procedure with boron trifluoride-methanol reagent for gas chromatographic analysis of ritalinic acid in urine.

Ritalinic acid (RITA), the major metabolite of methylphenidate (Ritaline) is extracted with a solid-phase C8 column. Following elution, methylation of the carboxylic group is performed with boron trifluoride-methanol as a reagent. The methyl ester of RITA which structurally corresponds to the parent compound methylphenidate is reextracted at pH 9-11. Each step of the analytical method has been systematically studied, particularly the parameters governing the esterification reaction with BF3-methanol. The recovery from the overall method is 96%. The limit of detection is 0.05 micrograms ml-1 with GC-NPD for a 10-ml urine sample. The method has been successfully applied to the detection and quantitation of RITA in urine specimens. The specificity of the methylated RITA peak has been verified by GC-MS in scan mode. Use of diazomethane or sulphuric acid is thus replaced by the use of a less hazardous reagent.