Figures index

From

Monitoring pH Using Alizarin-modified Commercial Screen-printed Electrodes

Achim Habekost

World Journal of Chemical Education. 2020, 8(4), 163-169 doi:10.12691/wjce-8-4-4
  • Figure 1. Redox of the anthraquinone moiety
  • Figure 2. Redox of the catechol moiety
  • Figure 3. Schematic representation of the alizarin-modified pyrolytic graphite
  • Figure 4. a: Reversible oxidation of alizarin: 2-electron, 2-proton process, b: Nucleophilic attack by water followed by further oxidation and tautomerism [6]
  • Figure 5. CV of alizarin (DRP 110ALI unmodified) and MWCNT-SPE with alizarin / Nafion modified with Nafion). Dotted line: Sampling rate 0.02 V/s, unmodified DRP 110ALI-SPE. Black solid line: Scan rate 0.02 V/s, MWCNT/alizarin/Nafion-SPE. Dashed line: scan rate 0.2 V/s MWCNT/alizarin/Nafion-SPE (see the different current scales). Numbers refer to the above reaction scheme. The star symbolizes the reaction product of the dicarbonyl, see reaction (2). Wide arrow: scan direction
  • Figure 6. pH dependence of MWCNT/alizarin/Nafion-SPE. Solid line: pH 7; dashed line: pH 4; dotted line: pH 1. Numbers refer to the above reaction scheme. The arrows indicate the two oxidation reactions (1) and (2)
  • Figure 7. Comparison of unmodified DRP 110 ALI (dotted line) and modified DRP 110 ALI with less (solid line) and more alizarin (dashed line). Scan rate: 0.05 V/s
  • Figure 8. Ratio between cathodic and anodic current peaks. Black: scan rate 0.05 V/s; dotted: scan rate 0.5 V/s
  • Figure 9. pH dependence of the oxidation potential: Ep = -58 mV/pH + 0,8 V
  • Figure 10. Anodic current peaks as a function of pH. Arrow indicates increasing pH. Insert: Current peak at pH 11. Electrochemical method SWV
  • Figure 11. pH dependence of the oxidation potential: Ep = -64 mV/pH + 0,77 V
  • Figure 12. CV recorded twenty times in a row (black lines). After one week, the same SPE was used for the same procedure (red lines). Scan rate 0.05 V/s