Electrochemical Detection of Polyanions on Polypyrrole/DMMB Nanowire Composite Film Modified Electrode

Scale inhibitor is a type of water-soluble polyanions with some special anionic group to prevent the water from scaling in a water recirculating system. Usually, a large amount of the polymers was added in order to maintain the good performance. However, overfeeding of the chemicals will result in high operation cost. Therefore, it is necessary to monitor the content of the polyanions in the cooling water to keep the good performance, and at the same time to save the added amount of the scale inhibitor. The common methods of estimating the concentration of the polymer include fluorometric method ¹, turbidimetric method ² and colorimetric method ³. These techniques are often unsatisfactory due to dye contamination, complicated steps, etc. The electrochemical quantification of these polyanions is ever reported based on the ion-selective electrode ⁴. It has been demonstrated that the polyanions HPS-1 presented a strong adsorption on the PPY modified electrode ⁵. The phenothiazine dyes have a good interaction with anionic polymers³, by which the direct polymer detection can be realized. Polypyrrole (PPy) is a particularly interesting ion-exchange material in the development of electrochemically controlled delivery devices and separation systems for charged species. In this report, the solid-state electrochemical device was developed with phenothiazine dye dimethyl methylene blue (DMMB) and conducting polymer PPy simultaneously immobilized on the electrode surface by electrochemical polymerization. The PPy-DMMB composite film presents a uniform nanowire structure. This network structured nano wire was characterized by scanning electric microscopy (SEM) and FTIR. The electrochemical response of polyanions HPS-1 on the PPy-DMMB modified electrode has been studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). This nano wire composite film modified electrode shows a good electrochemical response to HPS-1 due to the large specific surface area of the PPy nanowire structure, and the synergetic function of DMMB and PPy. Under the optimized conditions (such as concentration of pyrrole monomer, concentration of support electrolyte), polyanions quantification was achieved on the PPy-DMMB nanowire modified electrodes by electrochemical impedance spectroscopy with Fe(CN)₆ ^3-/4-   as the electroactive marker. The linear range of HPS-1 is between 2 ppm-35 ppm, with a detection limit down to 0.5 ppm(S/N=3). This method is very promising for monitoring the anionic-charged polymer in the industrial water system.

 Reference.

1. J. E. Hoots, S. Charles, C. C. Pierce, et. al  Monitoring and in system concentration control of polyelectrolytes using fluorochromatic dyes, US patent  US5389548.
2. M.J. Sader, "Turbidity Science", Technical Information Series--Booklet No. 11, from the HACH Technical Center for Applied Analytical Chemistry.
3. C. Steven, H. John, Rapid colorimetric method for measuring polymers in aqueous systems, patent  US6214627.
4. Z. Samec, A. Trojacek, J. Langmaier, E. Samcova, Cyclic voltammetry of biopolymer heparin at PCV plasticized liquid  Electrochem. Commun. 5(2003) 867-870.
5. J. Liu, Z. Zheng, Y. Liang, W. Cai, C. Wei.   Polymer Detection in the Industrial Water System by Electrochemical Method. US patent NO:8025789.