Monitoring of threo‐methylphenidate enantiomers in oral fluid by capillary electrophoresis with head‐column field‐amplified sample injection

Abstract

Threo-methylphenidate is a chiral psychostimulant drug widely prescribed to treat attention-deficit hyperactivity disorder in children and adolescents. An enantioselective CE-based assay with head-column field-amplified sample stacking for analysis of threo-methylphenidate enantiomers in liquid/liquid extracts of oral fluid is described. Analytes are electrokinetically injected across a short water plug placed at the capillary inlet and become stacked at the interface between plug and buffer. Enantiomeric separation occurs within a few minutes in a pH 3.0 phosphate/triethanolamine buffer containing 20 mg/mL (2-hydroxypropyl)-β-CD as chiral selector. The assay with six point multilevel internal calibration provides a linear response for each enantiomer in the 10-200 ng/mL concentration range, is simple, inexpensive, and reproducible, and has an LOQ of 5 ng/mL. It was applied to oral fluid patient samples that were collected up to 12 h after intake of an immediate release tablet and two different extended release formulations with racemic methylphenidate. Drug profiles could thereby be assessed in a stereoselective way. Almost no levorotary threo-methylphenidate enantiomer was detected after intake of the two extended release formulations, whereas this enantiomer was detected during the first 2.5 h after intake of the immediate release preparation. The noninvasive collection of oral fluid is an attractive alternative to plasma for the monitoring of methylphenidate exposure in the pediatric community.

Microassay for ketamine and metabolites in plasma and serum based on enantioselective capillary electrophoresis with highly sulfated γ-cyclodextrin and electrokinetic analyte injection

“…In order to explore the use of electrokinetic sample injection with cationic separation of the compounds, a 100 mM phosphate buffer (pH 3.0, prepared with disodium hydrogenphosphate and phosphoric acid) comprising 0.6–0.8% HS‐γ‐CD was employed as separation medium. The buffer was the same as used for the monitoring of methylphenidate stereoisomers in oral fluid by CE with head‐column field‐amplified sample injection . The pH 3.0 phosphate buffer was found to have a better baseline stability compared to the pH 2.5 BGE composed of Tris and phosphoric acid employed previously with hydrodynamic sample injection and anionic sample separation .…”

“…A water plug provides a region of very low conductivity. For analyte stacking, its length should be eight to ten times shorter . However, a short water plug does not provide the required barrier for HS‐γ‐CD.…”

Improving the sensitivity in chiral capillary electrophoresis

“…FASS has been employed in several works . On the one hand, submicromolar LODs were obtained for ten cathinone derivatives in a CEC system with amylose tris(5‐chloro‐2‐methyl‐phenylcarbamate) as a chiral stationary phase employing FASS .…”

Chromatographic and electrophoretic strategies for the chiral separation and quantification of d‐ and l‐threo methylphenidate in biological matrices

“…Migration velocities depend on mobility of the analyte, which can be optimized through changes in buffer ionic strength and pH (Boone et al , ). Reported enantiomer separations of d,l‐ threo ‐MPH by CE are performed in CZE mode and involve the addition of chiral selectors (Bach and Henion, ; Boone et al , ; Denk et al , ; Huang et al , ; Lee et al , ; Schneiderman et al , ; Theurillat and Thormann, ). CE chiral separations of d‐l‐ threo ‐MPH utilized cyclodextrins (CD) and their derivatives as chiral selectors (Ward and Hamburg, ).…”

“…Bach and Henion () report a validated LLE procedure for the enantioselective extraction of MPH from human urine samples into cyclohexane using sodium tetraborate buffer. Finally, Theurillat and Thormann () describe an extraction procedure employed for the isolation of MPH enantiomers from oral fluid, again using a hexane organic phase.…”