Non-transferrin-bound iron determination in blood serum using microsequential injection solid phase spectrometry – proof of concept

Non-transferrin-bound iron (NTBI) is a group of circulating toxic iron forms, which occur in iron overload or health conditions with dysregulation of iron metabolism. NTBI is responsible for increased oxidative stress and tissue iron loading. Despite its relevance as a biochemical marker in several diseases, a standardized assay is still lacking. Several methods were developed to quantify NTBI, but results show high inter-method and even inter-laboratory variability. Thus, the development of a consistent NTBI assay is a major goal in the management of iron overload and related clinical conditions. In this work, a micro sequential injection lab-on-valve (μSI-LOV) method in a solid phase spectrophotometry (SPS) mode was developed for the quantification of NTBI, using a bidentate 3,4–hydroxypyridinone (3,4-HPO) ligand anchored to sepharose beads as a chromogenic reagent. To attain SPS, the functionalized beads were packed into a column in the flow cell, and the analyte, NTBI retained as iron (III), formed a colored complex at the beads while eliminating the sample matrix. The dynamic concentration range was 1.62–7.16 μmol L−1 of iron (III), with a limit of detection of 0.49 μmol L−1 and a limit of quantification of 1.62 μmol L−1. The proposed μSI-LOV-SPS method is a contribution to the development of an automatic method for the quantification of the NTBI in serum samples.