Employment of Optimal Mixture Design to Optimize Selective and Sensitive Manganese (II) Potentiometric Sensor in Environmental and Biological Samples

A potentiometric sensor as a selective, straightforward, and sensitive device was prepared based on a carbon paste electrode (CPE) as an indicator electrode for determining manganese (II) ions in environmental water and biological samples. A novel and synthetic ligand, 5,5'-((2E,2'E)-2,2'-(1,2-diphenylethane-1,2-diylidene)bis(hydrazin-1-yl-2-ylidene))bis (4-amino-4H-1,2,4-triazole-3-thiol) (called BBP), which has a selective interaction with Mn2+ ion, was chosen as an ionophore in the CPE composite. An optimal mixture design was generated to optimize the CPE components' percentages, including BBP, MWCNTs, an ionic liquid, and graphite powder, and to investigate binary interactions between the component amounts. Effects of several modifier agents, such as MWCNTs, NH2-MWCNTs, and COOH-MWCNTs, were evaluated in the CPE composite. The ability of two binders (Paraffin oil and an ionic liquid ([Bmim][BF4])) in the CPE composite was compared, indicating that ionic liquid has a better response than paraffin oil due to an increase in electrical conductivity and flexibility of CPE. Under the CPE components optimization, the sensor displayed a wide pH range from 2.8 to 8.2, a short response time (5 s), and a long lifetime (11 weeks) for the Mn2+ ion determination. The sensor also has a wide linear range from 1.0x10-7-1.0x10-1 M with a LOD of 3.1x10-8 M and an R-squared of 0.998 without significant interfering effects of other ions for the Mn2+ ion measurement. The sensor performance was studied by analyzing river water, well water, and human urine samples, and the results were compared with flame atomic absorption spectrometry.