Enantiomeric quantification of ( S)-(+)-methamphetamine in urine by an immunoaffinity column and liquid chromatography–electrospray-mass spectrometry

Abstract

A method using an immunoaffinity column (IAC) and liquid chromatography–electrospray ionization mass spectrometry (LC/MS) for on-line detecting the presence of MA in the effluent was developed for the quantitative and enantiomeric determination of ( S)-(+)-methamphetamine ( d-MA) in urine. The IAC was made in our laboratory and utilized in the LC/MS to simultaneously extract and separate enantiomers of MA from urine samples. An aqueous ammonium acetate buffer was used as the mobile phase. Urine samples were spiked with racemic deuterated methamphetamine (MA-d 14) as internal standard (IS), filtered through a membrane, and injected into the LC/MS without any further pre-treatment. Protonated molecular ion of MA and MA-d 14 ( m/ z 150 and 164) were isolated and further fragmented, the respective product ions, m/ z 119 and 130, were collected for quantitative determination. This is an improvement of our previous method (A.C. Lua, Tsong-Yung Chou, J. Chromatogr. A 967 (2002) 191). In the previous method, MA was separated with HPLC, the efflux was fractionated and each fraction was either determined with an immunoassay or GC/MS. Monitoring of MA in the efflux is tedious and time consuming. Urine samples spiked with different concentrations of d-MA were measured by this method. A linear relationship exists in the 150–1050 ng/mL range, and the detection limit (defined as signal-to-noise ratio 3) of d-MA was determined to be 18 ng/mL. The linearity of the method for d-MA can be described by the equation ( Y = 1.415 × 10 −3 X + 0.034, correlation coefficient: r 2 = 0.999). Within run, accuracy and precision ( n = 6, relative error: −7.2 to +4.0% and relative standard deviation: 3.8–9.3%) of the method are fairly good.