A microfluidic paper-based analytical device for iodometric titration of ascorbic acid and dopamine

Abstract

A simple, rapid, and on-site iodometric titration with minimal preparation was devised utilizing a novel combination of traditional redox titration and microfluidic paper-based analytical devices (μPADs). The star-shaped pattern titration μPADs consists of a central sample loading zone connected to ten lateral reaction/detection reservoirs. The reaction reservoirs contain various concentrations of copper (II) acetate monohydrate with well-defined concentration gradient intervals and a fixed concentration of potassium iodide. This will result in a gradient of yellow color indicating iodine liberation as titrant in lateral reservoirs. The titration is stimulated when the test solution is applied to the central sample zone. As soon as the sample solution reaches the reaction zones (30 sec. after sample introduction), a constant concentration of amylose solution is added to the detection reservoirs, which serves as an indicator. The analyte is oxidized by the liberated iodine and the excess iodine reacts with amylose indicator, characterized by the formation of dark brownish-blue color. Therefore, the concentrations of target analyte solutions can be determined just in 30 sec., totally instrument-free and directly by naked-eye without calibration. The proposed μPADs are capable of determining ascorbic acid and dopamine solutions ranging from 1.0 × 10−5 M to 1.0 × 10−2 M. The detection lower limit is 1.0 × 10−5 M which is too difficult to measure using conventional volumetric iodometric titration. The reproducibility of the proposed method is lower than ± 5 % for five replicate measurements. The feasibility of the designed μPADs was confirmed by analysis of real samples and the results are highly consonant with those obtained from standard methods.