A technique for the speciation analysis of metal-chelator complexes in aqueous matrices using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

Abstract

Chelators, capable of creating soluble complexes with metals, may disrupt the natural speciation of metals in environmental matrices. Detection of environmental speciation of such complexes has remained challenging as obtaining the precise inherent nature of metal-chelator complexes is difficult by using routine techniques. Herein, we report a rapid and sensitive technique for the speciation analysis of complexes of five metal ions (Ni, Pb, Co, Fe and Ca) with two aminopolycarboxylate chelator variants, namely, EDTA (ethylenediaminetetraacetic acid) and EDDS (ethylenediamine-N,N'-disuccinic acid), including the simultaneous quantification of those complexes. EDTA is characterized as environmentally persistent among the chelators used in the current work whereas EDDS is biodegradable. The speciation analysis was performed using ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The separation was achieved by using hydrophilic interaction liquid chromatographic column. The effect of various operating parameters on analytes such as mobile-phase composition, buffer concentrations and pH, sample diluents, sample injection volume, and column temperature on the peak shape and sensitivity were systematically optimized. The dilution was the only requirement for preparing the samples for analysis. The average relative uncertainty was 2.4% with the average precision (as RSD, n= 7) of 3.5%. For the metal-EDTA complexes, LOD range was 3 to 76 nmol L–1 with satisfactory recovery from a simulated mix matrix (recovery: 79–97%) and river water by standard addition (recovery: 82–94%). For metal-EDDS complexes, LOD range was 66 to 293 nmol L–1 with recovery from a simulated mix matrix (recovery: 56–97%) and river water by standard addition (recovery: 61–91%). The proposed method will be applicable in speciation analysis and simultaneous detection of metal-chelator complexes from environmental samples.