Skip to main content
- Last updated
- 12:48, 15 Sep 2016
Save as PDF
- An analog or computer-controlled potentiostat with appropriate data acquisition capability (ask you laboratory instructor about potentiostat and data recorder).
- Electrochemical cell
- 1 - 3mm diameter flat tipped glassy carbon electrode
- Ag/AgCl reference electrode
- Pt auxiliary electrode
- Electrode polishing kit
- 100 ml of 10 mM AA in 0.10 M phosphate buffer at pH 2 containing 0.5 g/L Na2EDTA to prevent the oxidation of AA. It is recommended that the solution be deaerated to remove oxygen prior to adding AA. Store solution in a refrigerator when not in use. It is important to use high purity water and clean glassware. Record the concentration to three significant figures.
- 250 ml of stock 0.1 M phosphate buffer at pH 2.
- 50 ml of 2.0 mM AA in pH 2 phosphate buffer by dilution of stock solutions 1 and 2. Keep tightly sealed when not in use. Prepare daily from stock.
- 50 ml test sample by diluting 1:20 commercial fruit drink with the pH 2 phosphate buffer. Use immediately.
- Recommend the use of a 3.0 ml cell, with a 1.0 mm or 3.0 mm disk GC electrode, an Ag/AgCl reference and a Pt auxiliary electrode. It is recommended that rubber gloves be used to handle the cell and electrodes.
- Run #1: Fill the cell so that the electrodes are immersed in the 2.0 mM AA solution. Connect the electrodes to the potentiostat. All scans will be from 0.0 V to +0.6 V and back to 0.0 V at scan rates of 20 mV/s, 100 mV/s and 200 mV/s. Use the GC electrode without polishing (this will serve as the “inactive” electrode). Wait 2 minutes between scans to allow the concentration at the electrode surface to equilibrate with the bulk solution.
- Run #2: Repeat after removing and polishing the GC electrode with 0.05 μm alumina on a clean glass plate and rinse with pure water prior to use. Please refer to “Activation of Glassy Carbon Electrode” that is available as a Technical Note. Add the scan rates of 200 mV/s and 1.0 V/s and set the number of scans to 2. If the CV wave at 100 mV/s does not exhibit a sharp peak, as seen in Trace C of Figure 2, it may be necessary to polish the electrode first on a fine grit 0000 paper followed by alumina.
- Set the scan rate to 100 mV/s and obtain CV of AA at concentrations of 0.50 mM, 1.0 mM, 2.0 mM and 4 mM in pH 2 phosphate buffer. Run a background CV of the buffer without AA at these scanning rates to correct for the peak heights.
- Run duplicates of the fruit juice sample and determine its concentration by comparing the peak height to a calibration plot of concentration versus peak height, as determined in step #3. If the CV peaks are not sharp and well defined, re-polish with alumina to activate the electrode.
- It is recommended that you save all CV data on the hard drive or memory card with file names or in a folder with your name for future reference. If data are saved as an ASCII file, transfer data to a Microsoft EXCEL program and re-plot the data files. Excel gives you options to make different formatted graphs.