In-situ droplet assay on wax-modified paper for rapid and trace determination of Fe3+ in water

Doaa Abdulrazzaq Wazuddin, Liyakat Hamid Mujawar*, Tharawat Nabil Abduljabbar, Mohommad Soror El-Shahawi

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


The present study is focused on developing a colorimetric spot assay for direct determination of Fe3+ in water. The established method was based upon the use of wax modified paper as a low-cost platform onto which a droplet-based colorimetric reaction between aqueous Fe3+ and 2-(5-Bromo-2-pyridylazo)-5-(diethylamino) phenol (5-Br-PADAP) was executed. The wax-modified paper was characterized by goniometry that clearly showed a substantial increase in the water contact angle (θ) from 0° to ~123°. Morphological differences in the cellulose fibers of unmodified and modified paper were further confirmed via SEM and AFM analysis. The proposed assay was simple to execute and the resulting color change was readable via naked eyes with total assay time not exceedingly more than 10 min. The limit of detection and linear dynamic range for Fe3+ assay executed on the wax-modified paper were 0.01 ppm and 0.1–100 ppm, respectively. The attractive features of the established assay mainly include its simplicity, fast response time, inexpensive modification/platform, low reagent/analyte volume requirement and instrument-free readout. Hence, the proposed paper-based chemosensor can serve as a promising tool for point-of-use application in resource limiting regions especially dealing with iron contamination.

Original languageEnglish
Article number106723
JournalMicrochemical Journal
Number of pages9
Publication statusPublished - 2021


  • Droplet assay
  • Fe determination
  • Hydrophobic paper
  • Marine water
  • Paraffin wax


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