Development of microfluidic paper based analytical devices (µPADS) for the detection of calcium and magnesium ions

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
Buddhika Liyana Pathirannahel (Creator)
Institution
Western Carolina University (WCU )
Web Site: http://library.wcu.edu/
Advisor
Scott Huffman

Abstract: Microfluidic paper-based analytical devices (µPADs) have been developed using several patterning technologies to reproducibly create inexpensive lab-on-chip type analytical tools. Consequently, these devices are useful for field deployable measurements in the areas of healthcare diagnostics, environmental monitoring, and forensic analysis. These devices are portable, cost effective and easily reproducible. One of the significant characteristics of µPADs is that they are extremely versatile. Thus, they can be modified to any application, particularly in low resourceful settings. The goal of this project was to create novel microfluidic paper-based analytical devices µPADs that were able to detect and quantify the presence of calcium and magnesium ions in water samples using a simple complexometric titration. The work involved in this project can be divided into two parts. The first part was spent on optimizing parameters that are needed to produce µPAD consistently and repeatedly using wax printing method. The parameters studied are the melting temperature, the melting time and their effect on the barrier width and the channel width. Based on the results that were obtained, µPADs were designed with ten reservoirs in the middle of channels and ten reservoirs at the end of the channels. The detection of the calcium and magnesium was performed on the µPADs using typical complexometric titrations. Two separate titration reactions were carried out on µPADs that were prepared separately. The first step was to determine the total water hardness which is the total concentration of magnesium and calcium ions in water. The pH of the µPADs for this analysis was maintained at pH 10 using CAPS buffer. The ten reaction reservoirs contained various amounts of EDTA, whereas a constant amount of EBT was added to all detection reservoirs. When the amount of total calcium and magnesium ions exceeded that of the EDTA in the reaction reservoirs, free metal ions penetrated the detection reservoirs resulting a color reaction from EBT. Therefore, the first detection reservoir with no color change determined the total concentration of calcium and magnesium ions which is equal to total hardness. Next step was to determine the individual calcium ion concentration at pH 13. The pH on the µPADs was achieved using 10 M KOH. Here the ten reaction reservoirs contained various amounts of EDTA while the detection zone contained a constant amount of calcon as the metal indicator. When a water sample containing calcium and magnesium ions are added to the sample zone, magnesium ions get precipitated as a solid while free calcium ions get penetrated to the reaction and detection zones. Here, the calcium concentration is determined based on the concentration of the first reaction zone with no color change. The effects of other metal ions that might be present in the water on the µPADs were also studied. It was found that the presence of Cu2+, Ni2+, Al3+, Mn2+ and Fe3+ ions could interfere with the results. The µPADs determined the concentration of metal ions at orders of magnitude ranging from 0 - 90 mM as well as from 0 - 9 mM. The analysis of unknown water samples obtained from the lakes, wells and rivers was also demonstrated in the field using the µPAD, and the results agreed well with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES).

Additional Information

Publication
Thesis
Language: English
Date: 2018
Keywords
calcium and magnesium, chelate titrations, microfluidic paper based analytical devices, water hardness

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