Iron Determination in Natural Waters Using a Synthesised 3-Hydroxy-4-Pyridione Ligand in a Newly Developed Microfluidic Paper-Based Device

This work describes the development of an iron sensor based on a microfluidic paper-based technique, to attain iron quantification in natural waters. A new water-soluble naphthalene-3-hydroxy-4-pyridione ligand was used as a colour reagent, as it formed an orange complex with iron. As a newly described ligand, several chemical and physical parameters, namely, the sample and reagent volumes and reagent concentrations, were studied related to the formation of the coloured complex. The microfluidic paper-based analytical device (mu PAD) assembly, namely, the use of different types of filter paper and different numbers of layers, was developed to obtain the best performance. Under the optimal conditions, a linear correlation was obtained in the range of 0.25-2.00 mg/L of iron, with a minimum detectable value of 0.07 mg/L. The proposed mu PAD method was validated by an analysis of the certified samples and by a comparison of the tested water samples with the inductively coupled plasma (ICP) results (RE < 10%). Then, the mu PAD device was successfully applied to the determination of iron in tap water, well water, river water, and seawater, with no need for any prior sample pre-treatment; recovery studies were also performed (average = 100.3% with RSD = 4.2%).