Objective: To develop a routine method for detecting methylphenidate (Ritalin) use among drug abusers using liquid chromatography-tandem mass spectrometry (LC/MS/MS). The new methodology was designed to replace less reliable and/or more expensive and time-consuming techniques (GC/MS and ELISA) currently employed in our laboratory, and to provide a combined one-step screening and confirmation LC/MS/MS method.
Design and methods: Because methylphenidate abuse is very prevalent in Saskatchewan, there is a demand to provide high volume urine screening both to detect abuse, and to monitor compliance. Random urine samples sent for drugs of abuse testing, standards, and controls were diluted 1:100 in methanol. Diluted specimens were injected directly into an Agilent 1100 liquid chromatograph coupled to a Sciex API 2000 mass spectrometer. The method utilized selected reaction monitoring (SRM) as well as an electrospray ionization source (EIS) to detect both urinary methylphenidate and the more prevalent metabolite, ritalinic acid (RA).
Results: There appeared to be little or no sacrifice in sensitivity because the higher dilutions exhibited much less matrix effect. Limit of quantitation (LOQ) for methylphenidate was 100 nM and 500 nM for RA. Linear calibration curves from 100 to 1000 nM for Ritalin and 500 to 5000 nM for RA were acquired. Imprecision of spiked and true specimens did not exceed 10% and at the LOQ, it was less than 20%.
Conclusions: A rapid, sensitive, reliable, and highly specific method by LC/MS/MS for detecting methylphenidate and its metabolite, RA, were developed. Both the cost and performance of the LC/MS/MS method were superior to GC/MS or ELISA, and it allows use of a single rapid procedure for both screening and confirmation.