Spectrophotometric and Fluorometric Methods for the Determination of Fe(III) Ions in Water and Pharmaceutical Samples

Chemical sensors based on mesoporous silica nanotubes (MSNTs) for the quick detection of Fe(III) ions have been developed. The nanotubes' surface was chemically modified with phenolic groups by reaction of the silanol from the silica nanotubes surface with 3-aminopropyltriethoxysilane followed by reaction with 3-formylsalicylic acid (3-fsa) or 5-formylsalicylic acid (5-fsa) to produce the novel nanosensors. The color of the resultant 3-fsa-MSNT and 5-fsa-MSNT sensors changes once meeting a very low concentration of Fe(III) ions. Color changes can be seen by the naked eye and tracked with a smartphone or fluorometric or spectrophotometric techniques. Many experimental studies have been conducted to find out the optimum conditions for colorimetric and fluorometric determining of the Fe(III) ions by the two novel sensors. The response time, for the two sensors, that is necessary to achieve a steady spectroscopic signal was less than 15 s. The suggested methods were validated in terms of the lowest limit of detection (LOD), the lowest limit of quantification (LOQ), linearity, and precision according to International Conference on Harmonization (ICH) guidelines. The lowest limit of detection that was obtained from the spectrophotometric technique was 18 ppb for Fe(III) ions. In addition, the results showed that the two sensors can be used eight times after recycling using 0.1 M EDTA as eluent with high efficiency (90%). As a result, the two sensors were successfully used to determine Fe(III) in a variety of real samples (tap water, river water, seawater, and pharmaceutical samples) with great sensitivity and selectivity.