Green Microextraction, Paper-Based Technique, and Smartphone Sensing for Sustainable Determination of Nicotinamide in Pharmaceuticals and Blood Samples.

This study presents the development of two simple, sensitive, and selective microextraction and preconcentration procedures for determining nicotinamide (NAM) in pharmaceutical formulations and blood samples. The methods utilize the König reaction, where cyanogen chloride, formed by reacting potassium thiocyanate with sodium hypochlorite in an acidic medium, interacts with NAM and couples with buffered barbituric acid at pH 3.5 to form a pink polymethine dye. This dye is extracted into an isobutanol layer using tetrabutylammonium bromide and exhibits maximum absorption at 560 nm for spectrophotometric quantification. In the smartphone paper-based (SPB) method, the dye is applied to a paper strip, captured by a smartphone, and analyzed for red, green, and blue components. Both methods were thoroughly evaluated for key parameters, demonstrating adherence to Beer's law over a NAM concentration range of 1.0-7.8 µg/mL, with limits of detection of 0.76 µg/mL for the spectrophotometric method and 0.91 µg/mL for the SPB method. Our SPB combines paper-based analysis, smartphone detection, and microextraction for the first time, offering a cost-effective, portable, and sensitive solution for NAM assay in plasma. A comparison with the established high-performance liquid chromatography method, using statistical tests, showed no significant differences, confirming the reliability of these novel methods.