Simple colorimetric ammonium assay employing well microplate with gas pervaporation and diffusion for natural indicator immobilized paper sensor via smartphone detection

Abstract

© 2019 Elsevier B.V. A simple and cost-effective analytical device based on gas pervaporation and diffusion method for determination of ammonia is proposed. The proposed device is consisted of a well microplate as a donor chamber and a natural indicator-immobilized paper (butterfly pea flower extract) as an acceptor sensor. This allows microliter-scale solution handling. The sample preparation step involved conversion of ammonium ion to ammonia using an alkaline solution, following by gas pervaporation and then diffusion of ammonia across a PTFE membrane into a natural indicator-immobilized paper. The colorimetric change on the paper then was detected by either a smart phone camera or naked eye for quantitative or semi-quantitative analysis, respectively. Under the optimal condition, a linear calibration with a range of 10–100 mg/L ammonium-nitrogen was obtained. The method has a detection limit (3σ) of 4 mg/L ammonium-nitrogen, n = 9. This proposed device was successfully applied for determination of ammonia in swine farming wastewater and chemical fertilizer samples. It could simultaneously perform triplicate run of 18 samples in 15 min (72 samples/hr). The proposed device with pervaporation and diffusion method offers on-site assay and green chemical analysis with relatively high throughput.