Instruction Manual Carbon Dioxide Electrode EUTECH INSTRUMENTS PTE LTD. INSTRUCTION MANUAL CARBON DIOXIDE ION ELECTRODE 1 Instruction Manual Carbon Dioxide Electrode TABLE OF CONTENTS GENERAL INSTRUCTIONS ......................................................................................................................................... 3 Introduction ............................................................................................................................................................. 3 Required Equipment................................................................................................................................................ 3 Required Solutions .................................................................................................................................................. 3 GENERAL PREPARATION .......................................................................................................................................... 4 Electrode Preparation .............................................................................................................................................. 4 Checking Membrane ............................................................................................................................................... 4 Changing the Membrane ......................................................................................................................................... 4 Connecting the Electrode to the Meter.................................................................................................................... 4 Electrode Slope Check (with pH/mV meter)........................................................................................................... 4 Electrode Slope Check (with ion meter) ................................................................................................................. 5 MEASUREMENT ............................................................................................................................................................ 5 Measuring Hints ...................................................................................................................................................... 5 Sample Storage........................................................................................................................................................ 6 Sample Requirements.............................................................................................................................................. 6 Units of Measurement ............................................................................................................................................. 6 MEASUREMENT PROCEDURE .................................................................................................................................. 7 Direct Measurement ................................................................................................................................................ 7 Direct Measurement of Carbon Dioxide (using a pH/mV meter) ........................................................................... 7 Direct Measurement of Carbon Dioxide (using an ion meter) ................................................................................ 8 ELECTRODE CHARACTERISTICS ........................................................................................................................... 9 Reproducibility........................................................................................................................................................ 9 Interferences ............................................................................................................................................................ 9 Effect of Dissolved Species..................................................................................................................................... 9 Temperature Influences........................................................................................................................................... 9 Electrode Response ............................................................................................................................................... 10 Limits of Detection................................................................................................................................................ 11 pH Effects.............................................................................................................................................................. 11 Electrode Life........................................................................................................................................................ 11 Electrode Storage .................................................................................................................................................. 11 ELECTRODE THEORY............................................................................................................................................... 11 Electrode Operation............................................................................................................................................... 11 Carbon Dioxide Chemistry.................................................................................................................................... 12 ELECTRODE APPLICATION .................................................................................................................................... 13 Carbon Dioxide Content of Wines and Carbonated Beverages ............................................................................ 13 Carbonate Content in Groundwater....................................................................................................................... 14 Carbonate Measurements in Concentrated Ammonium Hydroxide...................................................................... 14 TROUBLESHOOTING GUIDE................................................................................................................................... 15 Meter ..................................................................................................................................................................... 15 Glassware .............................................................................................................................................................. 15 Electrodes .............................................................................................................................................................. 15 Standards ............................................................................................................................................................... 16 Sample................................................................................................................................................................... 16 Technique .............................................................................................................................................................. 16 TROUBLESHOOTING HINTS.................................................................................................................................... 17 Checking the Electrode Inner Body ...................................................................................................................... 19 SPECIFICATIONS ........................................................................................................................................................ 20 ORDERING INFORMATION ..................................................................................................................................... 20 2 Instruction Manual Carbon Dioxide Electrode EUTECH INSTRUMENTS PTE LTD. CARBON DIOXIDE GAS-SENSING ELECTRODE INSTRUCTION MANUAL GENERAL INSTRUCTIONS Introduction Eutech Carbon Dioxide Gas-Sensing Electrode is used to measure carbon dioxide, carbonate, and bicarbonate in aqueous solutions quickly, simply, accurately, and economically. With a flowthrough cap, the electrode can be used in flow-through applications. Required Equipment 1. 2. A pH/mV meter or an ion meter, either line operated or portable. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the meter in the mV mode. A magnetic stirrer. Eutech Carbon Dioxide Gas-sensing Electrode, Code no. EC-C02-01. 3. 4. Required Solutions 1. 2. Deionized or distilled water for solution preparation. Eutech Carbon Dioxide Standard, 0.1M NaHCO3, Code no. EC-SCS-CO1-BT. To prepare this solution from your own laboratory stock, half fill a 1 liter volumetric flask with distilled water and add 8.40 grams of reagent-grade NaHCO3. Swirl the flask gently to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several times to mix the solution. Eutech Carbon Dioxide Standard, 1,000 ppm NaHCO3 as CO2, Code no. EC-SCS-CO2BT. To prepare this solution from your own laboratory stock, half fill a one liter volumetric flask with distilled water and add 1.91 grams of reagent-grade NaHCO3. Swirl the flask gently to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several times to mix the solution. Eutech Carbon Dioxide Standard, 100 ppm NaHCO3 as CaCO3, Code no. EC-SCS-CO3BT. To prepare this solution from your own laboratory stock, half fill a one liter volumetric flask with distilled water and add 0.084 grams of reagent-grade NaHCO3. Swirl the flask gently to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several times to mix the solution. Eutech Carbon Dioxide Buffer Solution, Code no. EC-ISA-CO1-BT. To prepare this solution from your own laboratory stock, half fill a 1 liter volumetric flask with distilled 3 3. 4. 5. Instruction Manual Carbon Dioxide Electrode water, add 294 grams of Na3C6H5O7.2H2O (sodium citrate dihydrate). Swirl the flask gently to dissolve the solid. Fill the flask to the mark with distilled water. Stir the solution and adjust the pH of the solution to 4.5 with concentrated HCl. This buffer is used to adjust the pH of the solution to the operating range of the electrode. To each 100 ml of sample and standard solution, add 10 ml of carbon dioxide buffer. GENERAL PREPARATION Electrode Preparation This electrode is shipped dry. Before using, unscrew the large cap (See Figure 5), and remove the inner glass electrode from the outer body. Fill the outer body with 2 to 3 ml of internal filling solution. Place inner glass electrode into the outer body, and screw on the large cap until finger tight. Place the assembled electrode in an electrode holder with a 20o angle from the vertical to avoid trapping air bubbles at the bottom of the electrode. Checking Membrane A small hole of any size on the membrane or breakage of the membrane causes failure of the electrode. It is recommended to check the membrane on every newly assembled electrode. 1. 2. 3. 4. Connect a newly assembled electrode to a pH/mV meter. Lower the electrode tip in distilled water. Record the reading after stirring the distilled water for about 15 minutes. Add proper buffer solution (see section Required Solutions) to the distilled water. A drastic change in the reading in a positive direction indicates damage of the membrane. Changing the Membrane Unscrew the small cap from the outer body and remove the old membrane cartridge from the small cap. Insert the new membrane cartridge into place, and re-assemble the electrode. (See Figure 4.) Connecting the Electrode to the Meter Connect the electrode to the meter according to the meter manufacturer's instructions. No external reference electrode is required. To prevent air entrapment, mount the electrode at a 20o angle from the vertical. Electrode Slope Check (with pH/mV meter) (Check electrodes each day) 1. To a clean, dry, 150 ml beaker, add 90 ml of distilled water and 10 ml of carbon dioxide buffer. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the millivolt mode, lower the electrode tip into the solution. Remove air bubbles by redipping probe. 4 Instruction Manual Carbon Dioxide Electrode 2. 3. Using a pipet, add 1 ml of 0.1M or 1,000 ppm standard into the solution. When the reading has stabilized, record the mV value. Using a pipet, add 10 ml of the same CO2 standard used above to the beaker. When the reading has stabilized, record the mV value. Determine the difference between the two readings. The electrode is operating correctly if a difference of 56 ± 3 mV is found, assuming the solution temperature is between 20o and 25oC. See the TROU ...