Analytical Sciences

Microfluidic Analysis with Front-Face Fluorometric Detection for the Determination of Total Inorganic Iodine in Drinking Water

Prawpan INPOTA,*1,*2 Kamil STRZELAK,*3 Robert KONCKI,*3 Wisaroot SRIPUMKHAI,*4 Wutthinan JEAMSAKSIRI,*4 Nuanlaor RATANAWIMARNWONG,*2,*5 Prapin WILAIRAT,*2,*6 Nathawut CHOENGCHAN,*2,*7 Rattikan CHANTIWAS,*1,*2 and Duangjai NACAPRICHA*1,*2

*1 Center of Excellence for Innovation in Chemistry and Department of Chemistry, Faculty of Science, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
*2 Flow Innovation Research for Science and Technology Laboratories (FIRST Labs.), Thailand
*3 University of Warsaw, Department of Chemistry, Pasteura 1, 02-093 Warsaw, Poland
*4 Thai Microelectronics Center (TMEC), Chachoengsao 24000, Thailand
*5 Department of Chemistry, Faculty of Science, Srinakharinwirot University, Sukhumwit 23, Bangkok 10110, Thailand
*6 National Doping Control Centre, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
*7 Department of Chemistry and the Applied Analytical Chemistry Research Unit, Faculty of Science, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road, Bangkok 10520, Thailand

A microfluidic method with front-face fluorometric detection was developed for the determination of total inorganic iodine in drinking water. A polydimethylsiloxane (PDMS) microfluidic device was employed in conjunction with the Sandell–Kolthoff reaction, in which iodide catalyzed the redox reaction between Ce(IV) and As(III). Direct alignment of an optical fiber attached to a spectrofluorometer was used as a convenient detector for remote front-face fluorometric detection. Trace inorganic iodine (IO₃⁻ and I⁻) present naturally in drinking water was measured by on-line conversion of iodate to iodide for determination of total inorganic iodine. On-line conversion efficiency of iodate to iodide using the microfluidic device was investigated. Excellent conversion efficiency of 93 – 103% (%RSD = 1.6 – 11%) was obtained. Inorganic iodine concentrations in drinking water samples were measured, and the results obtained were in good agreement with those obtained by an ICP-MS method. Spiked sample recoveries were in the range of 86%(±5) – 128%(±8) (n = 12). Interference of various anions and cations were investigated with tolerance limit concentrations ranging from 10⁻⁶ to 2.5 M depending on the type of ions. The developed method is simple and convenient, and it is a green method for iodine analysis, as it greatly reduces the amount of toxic reagent consumed with reagent volumes in the microfluidic scale.

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