The schematic of the polyethylene Pasteur pipette-based USAEME procedure is shown in Fig. 1. Briefly, an aliquot of 6 mL sample solution was placed in an 8-mL Pasteur pipette using a 10-mL plastic syringe. Thirty microliters of the extraction solvent
(isooctane) were injected into the sample solution. After the injection, the pipette was placed in an ultrasonic water bath. An emulsion formed during the ultrasonication. After a 30 s sonication at 35 kHz of ultrasound frequency and 0.32 kW of power at 25
±2 ◦C, the emulsion was separated into two phases by centrifugation at 4000 rpm for 5 min. The pipette bulb was then squeezed slightly, and the upper layer comprising the organic extract moved into the narrower stem of the pipette. This permitted the convenient retrieval of the extract using a 10-L GC microsyringe. One microliter of the extract was injected into the GC–MS system for analysis. The used pipette was discarded to avoid carryover problems.