SEQUENTIAL-INJECTION EXTRACTION FOR SAMPLE PREPARATION

This report introduces a flow-based extraction method where an aqueous sample and organic solvent are injected sequentially into an extracti on coil, then mixed and separated due to the differential flow velocit ies of the aqueous and organic phases. A 500 mu l aqueous sample is pr opelled through a 50 mu l segment of organic solvent whose how is impe ded due to hydrophobic interactions with the walls of a Teflon extract ion coil. This wall drag allows the faster moving aqueous sample to pe netrate through and ultimately separate from the slower organic solven t. These steps are repeated with a back extraction into a second aqueo us segment (100 mu l) that is collected and analyzed with high-pressur e liquid chromatography (HPLC). The configuration of this novel sequen tial-injection extraction (SIE) system allows ease of changing reagent s and uses minimum organic solvent volumes, as it avoids continuous pu mping of reagents. Barbiturates (phenobarbital, amobarbital, pentobarb ital and secobarbital) and serotonin re-uptake inhibitors (SRIs) - ven lafaxine, paroxetine, sertraline and norsertraline - were extracted as model acidic and basic compounds from urine into a 1:4 (v:v) mixture of l-octanol and butyl chloride and back extracted into 0.45 M NaOH an d 0.18 M H3PO4, respectively. Absolute recoveries of the analytes were : venlafaxine 29%; paroxetine 30%; norsertraline 25%; sertraline 20%; phenobarbital 11%; amobarbital 24%; pentobarbital 23%; and secobarbita l 27%. The sample throughput, including extraction and back extraction , was 20 samples h(-1).