Magnetic immobilization of amine-functionalized magnetite microspheres in a knotted reactor for on-line solid-phase extraction coupled with ICP-MS for speciation analysis of trace chromium

Abstract

The use of magnetic microspheres and nanoparticles for sample extraction in analytical chemistry has received increasing interest. However, previous magnetic particle-based solid-phase extraction (SPE) is usually performed in a batch mode. In this work, we report magnetic immobilization of amine-functionalized magnetite (Fe3O4) microspheres (AF-MMPs) onto the inner walls of a knotted reactor (KR) for on-line SPE coupled with ICP-MS for speciation analysis of trace chromium. A tubular magnet is sufficient to immobilize AF-MMPs onto the inner walls of a KR without the need for any frits or plugs. Sensitive speciation analysis of trace CrIII and CrVI in water was achieved based on selective on-line SPE of either CrIII and CrVI under controlled pH conditions on an AF-MMPs magnetically immobilized KR integrated into a flow injection system with on-line ICP-MS detection without the need for extra oxidation/reduction. On-line SPE of 2.4 mL aqueous solution gave an enhancement factor of 96 for CrIII and 47 for CrVI, a detection limit of 1.5 ng L−1 for CrIII and 2.1 ng L−1 for CrVI at a sample throughput of 23 h−1. The precision (RSD) for eleven replicate measurements of 100 ng L−1 CrIII and CrVI was 1.9% and 4.5%, respectively. The batch-to-batch reproducibility (RSD) for three parallel prepared AF-MMPs packed KRs for the SPE of CrIII and CrVI at 100 ng L−1 was less than 5.5%. One AF-MMPs packed KRs can be used for at least 75 cycles of preconcentration without significant loss of extraction efficiency. The developed method was successfully applied to the speciation analysis of trace CrIII and CrVI in drinking water samples.