ABSTRACT
Microextraction by packed sorbent (MEPS) has been directly hyphenated with ESI-MS for the rapid screening of opiates and codeine metabolites in urine. This study introduces a novel format of MEPS that incorporates a two-way valve in the barrel of the syringe enabling the direction of liquid flow to be manipulated. Controlled directional flow (CDF) MEPS allows sharp, concentrated sample bands to be delivered directly to the MS in small volumes and effectively eliminates the need to optimize elution. The method optimization assessed the recovery, matrix effects, and the speed of infusion, all critical variables for optimum ESI performance. Matching extraction workflows demonstrated a reduction in carryover from 65% for conventional MEPS to only 1% for CDF MEPS. The recovery (<89% for 50 µL sample), matrix effects (<42%), linearity (r(2) > 0.99), and LODs (<5 ng/mL) were determined to demonstrate method performance. The optimized approach was employed for the screening of codeine metabolites in urine. The ion trace revealed sharp sample bands corresponding to the codeine metabolites. At-line MEPS-ESI-MS allowed both sample preparation and analysis to be completed in only 5 min facilitating high throughput and alleviating the burden of method development.
