The manifold of flow injection solid-phase extraction is illustrated in Fig. 2. The FI-SPE procedure for GC–MS detection runs through four steps: (1) with pump 2 on and injection valve in the fill position (Fig. 2a), water sample was introduced into the MWCNTs packed micro-column for preconcentration; (2) with pump 2 off and pump 1 on (Fig. 2a), an air flow was introduced to remove the residual solution in the micro-column; simultaneously, a 0.4 mL elute loop was filled with methanol; (3) with the injector valve turned to the injection position (Fig. 2b), an air flow was introduced to drive the methanol in the elute loop into the micro-column for elution; (4) the eluates were collected in an eppendorf tube, and aliquots of 1 μL were manually injected splitless into the gas chromatograph for GC–MS detection.