A Simple and Green Approach for Colorimetric Ammonia Determination by Combining Pervaporation With Paper Impregnated Anthocyanins Extracted From Red Cabbage

This work reports on the development of a simple, green and inexpensive analytical method utilizing a microwell plate for ammonia determination by combining pervaporation with a paper-based colorimetric sensor. The method is based on the conversion of ammonium ions to ammonia gas by alkalinization of water samples using powdered calcium hydroxide. The generated ammonia gas diffuses freely across the headspace to a paper-based sensor impregnated with natural anthocyanins extracted from red cabbage using deionized water as a non-toxic solvent. The reaction causes the paper sensor to change color from pink to blue, and the sensor is then scanned on a flatbed scanner to quantify ammonia by correlation to the reflectance of the blue spot on the paper sensor. Under the optimal conditions, a working range of 1.0-25.0 mg N l^-1 was obtained. The limit of detection and the limit of quantification were found to be 0.29 and 0.98 mg N l^-1, respectively. The method was successfully applied for determining total ammonia in water samples with recoveries in the range of 89.6-110.5%. No significant difference was observed between this method and the phenate spectrophotometric standard method.

Keywords: ammonia; calcium hydroxide powder; red cabbage anthocyanins; paper-based colorimetric sensor

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                                           E-mail: wiboon.pra@kmitl.ac.th