Sequential speciation analysis of heavy metals on suspended particulate matter in water using electrochemical mass spectrometry

Abstract

Speciation analysis of heavy metals in suspended particulate matter (SPM) in water helps evaluate health risks, understand pollution status, trace pollution sources, and select a remediation approach. In this study, electrochemical mass spectrometry (EC-MS), which combines extraction, reaction and electrolysis with in situ electrospray ionization mass spectrometry (ESI-MS), is established to directly analyze heavy metal speciations in SPM. The samples were first collected in a homemade electrolytic cell by filtration, followed by sequential extraction. Water and methanol were first used to extract water-soluble and organic metal speciations, respectively. EDTA-2Na was used to react with the insoluble metal to form a soluble EDTA-metal chelate. For elemental speciation, electrolysis was used to convert them into metal ions. The extracted speciations were online and transferred to ESI for ionization. Four kinds of speciations, including water-soluble, organic, insoluble, and elemental could be detected in 1 hour with high sensitivity. A proof-of-concept application was carried out to sequentially analyze metal speciation in the SPM in a lake. The experimental results indicated that the SPM from the lake water contained Zn, Cu, Mn, Pb, and Fe in a water-soluble state, Pb, Zn, Cu, and Ni were in an insoluble state, and no heavy metals in organic and elemental states were found. Compared with the traditional methods, this method featured no complex matrix separation process, less sample consumption, and high analysis throughput, offering unique possibilities for advanced applications in environmental monitoring and risk assessment.