Complexometric and argentometric titrations using thread-based analytical devices.

This work describes analytical approaches based on simple complexometric and argentometric titrations leading to the color change of a novel microfluidic thread-based analytical device (µTAD). The device was fabricated from a cotton thread (15 cm) treated with indicator solution, providing an easy-to-use platform for rapid measurement of analyte concentration in aqueous solution. The thread was immobilized onto a support, being a polypropylene sheet or box platform, to facilitate loading of liquid samples. Interaction between the deposited reagents and analytes in the samples then occurred within a few minutes. This resulted in zones of color change with different lengths along the thread depending on the analyte concentration. The interaction zones can be analyzed by human eyes based on comparison of the zone lengths with the printed scales which are correlated with the analyte concentrations. Complexometric titration using µTADs was initially investigated for Mg(II) determination in water and rubber latex samples. These devices consisted of two threads which were pretreated with Eriochrome Black T (EBT) and then treated with ethylenediaminetetraacetic acid (EDTA) in N-cyclohexyl-3-aminopropanesulfonic acid (CAPS) buffer at pH 10. Both threads were tied together with a central knot before being attached to the box platform prior to the analysis. Load of sample solution (6 µL) resulted in the length of red-violet color product on the threads being proportional to the concentration of Mg(II) in waters and rubber latex samples with the working concentration range of 25-1000 mg L-1. In addition, µTAD with a supporting polypropylene sheet consisting of several threads treated with AgNO3 and K2CrO4 indicators was applied for argentometric titration of chloride ion in water and food seasoning samples. After sample loading (3 µL), the initially red-brown threads turned into white corresponding to formation of AgCl(s) on the threads with a working concentration range of 75-600 mg L-1. Greater selectivity towards Mg(II) and chloride compared with potential interference ions was also observed. All the developed μTADs were applied for analysis of real samples which showed results being in agreement with those obtained by classical titrations.