In this work, flowinjection (FI) on-lineprecipitation–dissolution ina knotted reactor (KR)was establishedand combined with a portable tungsten coil electrothermal atomicabsorption spectrometer (W-coil ET-AAS)firstly forpreconcentrationanddeterminationofultra-tracecadmium.Asanewinstrument,theapplicationoftheportable W-coil spectrometer was expanded to carry out on-line preconcentration and detection through the coupling with a KR system. A self-assembled FI system was employed to hyphenate the KR system with W-coil ET-AAS. The instrumental conditions and influencing factors relevant to KR efficiency, such as concentration of ammonia, pH, conditions of sampling and elution were studied systematically. The coupling improved the analyticalperformanceof theportable spectrometerconsiderably.Undertheoptimalconditions,thelimitof detection(LOD)forcadmiumwas0.006μg/L,withsensitivityenhancementfactor(EF)of41.Theestablishedmethod could beexpanded and used for on-line preconcentration and detection of some other trace metal ions.