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 themethanol in the elute loop into themicro-column
for elution; (4) the eluates were collected in an eppendorf tube,
and aliquots of 1 L were manually injected splitless into the gas
chromatograph for GC–MS detection.