Analysis of methylphenidate, ethylphenidate, lisdexamfetamine, and amphetamine in oral fluid by liquid chromatography‐tandem mass spectrometry

Christina R. Smith; Madeleine J. Swortwood

Abstract

Oral fluid is an alternative matrix that has proven to be useful for the detection of drugs. Oral fluid is easy to collect, noninvasive, and may indicate recent drug use. There are limited methods available that analyze cognitive stimulants in oral fluid. Cognitive stimulants are used to treat attention‐deficit/hyperactivity disorder (ADHD), a neurological disorder that emerges from lack of dopamine in the brain. To combat this disorder, medications inhibit dopamine and norepinephrine reuptake by blocking transporters in the brain. Though commonly diagnosed in children, ADHD may extend beyond adolescence and abuse of medications in college students is not uncommon. The goal of this study was to develop and validate a quantitative method for methylphenidate, ethylphenidate, lisdexamfetamine, and amphetamine in oral fluid using liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Analytes were isolated by solid‐phase extraction and analyzed on an Agilent 1290 Infinity II Liquid Chromatograph coupled to an Agilent 6470 Triple Quadrupole Mass Spectrometer. The linear range was 0.5–100 ng/ml (except lisdexamfetamine at 5–500 ng/ml). Bias and between‐run precision were acceptable (±11.0% bias and ±12.2%CV). No interferences or carryover were observed and dilution integrity was sustained. This validated method was applied to four authentic oral fluid samples collected with Quantisal® devices from college students. Lisdexamfetamine was quantified in one sample at 5.8 ng/ml while amphetamine was quantified in all four samples at 6.0–78.8 ng/ml. This is the first known quantitative method in oral fluid that includes these analytes using LC‐MS/MS and may give rise to interpretive value in a forensic toxicology setting.