An electrochemically-based submersible probe for in-situ monitoring of the total content of dissolved metal species is described. The flow-through sensor relies on the coupling of an internal on-line acidification of the collected samples with potentiometric stripping detection of the metals released from their complexes. The optimisation and characterisation of the new remote sensor have been carried out with trace measurements of cadmium and lead in the presence of EDTA and NTA. Elevated levels of these ligands (e.g. 0.05 and 1.0 mM EDTA and NTA, respectively) had no effect upon the cadmium and lead peaks, as compared to the complete disappearance of the response without the internal acid delivery. Such real-time measurements of the total form of dissolved heavy metals hold great promise for environmental and industrial monitoring. Other in-situ speciation sensing schemes are anticipated based on the versatility of the renewable-reagent flow probe.