| Vitamin C(Vit C) as a kind of essential nutrients for people, plays a vital role in disease prevention and treatment, but people can not synthesize of Vit C by themselves. People get Vit C only from diet and medication. Therefore, there is a vital significance to accurately determine the Vit C content in daily food and drug for maintaining good health, diet nutrition, health care, etc. At present, the methods used to test Vit C include titration, voltammetry, high performance liquid chromatography(HPLC), spectrophotometry and so on. These methods can meet the requirements in detecting Vit C, but they have different degrees of defects. For instance, titration has a low detection accuracy for non-ferrous material, the modified process of voltammetry electrode is complex and time consuming; HPLC method needs specialist operations, and the equipment is expensive, liquid phase spectrophotometry has a poor portability. Based on the above key problems above, relying on electrostatic spinning nanofiber membrane with high specific surface area, abundant pore structure, controllable packing density and the polyaniline with good redox activity and optical properties, this paper proposes to design and construct the polyaniline/polyamide 66 nano-fibers/nets membrane based colorimetric seneor for Vit C and hopes to develop a sensitive, accurate, easy operating, portable, low cost and suitable for on-site inspection system for Vit C detect. Specific work is as follows:Through chemical oxidation method we synthesized the polyaniline with good redox activity and optical properties. Electrospinning technology was used to prepare polyaniline/nylon 66 nanofibers/nets membrane. We investigated the influence of the concentration of polyaniline of the solution properties, fiber membrane morphology structure and the Vit C color response. By adopting field emission scanning electron microscopy and ultraviolet-visible diffuse reflection spectrum, determining the optimal concentration of polyaniline is 2.5%, and in this polyaniline concentration, the nanofibrous membrane has a larger specific surface area(31.23 m2/g) to provide favorable conditions for detecting Vit C in high sensitive. By optimizing the sensor detection process parameters of oxidation time(60 s) and reaction time(30 min), we manage to make the polyaniline/nylon 66 colorimetric test strip achieve optimal detection effect of Vit C.In addition, under the optimum testing conditions, with the aid of ultraviolet-visible diffuse reflection spectrum characterization, we research the sensitivity, selectivity and regeneration of repeated use of colorimetric test strip for Vit C detection. Results show that color change of colorimetric test strip by 50 ppb Vit C can be easily perceived by naked eyes and the strip has good selectivity and regeneration.Finally, we use the color reading application of smartphone to obtain the color parameters(R, G, B) of standard concentration of Vit C response data, and produce standard color-difference map. The measured concentration range is 50 ppb to 400 ppm, we provide a quantitative analysis for Vit C. Based on principal component analysis(PCA), and obtain the first principal component(PC1) of R, G and B, then PC1 is used to elaborate standard curve. In the two concentration range 50 ppb to 3 ppm and 4 ppm to 400 ppm, PC1 has a good linear relationship with Vit C concentration logarithm, the correlation coefficients are 0.953 and 0.974. The PC1-Vit C standard curve can be used to quantify the concentration of Vit C. This method provides a new way for colorimetric quantitative analysis. |
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