Instruction Manual Carbon Dioxide Electrode EUTECH INSTRUMENTS PTE LTD.
Instruction Manual Carbon Dioxide Electrode TABLE OF CONTENTS GENERAL INSTRUCTIONS ......................................................................................................................................... 3 Introduction ............................................................................................................................................................. 3 Required Equipment................................................................................................
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. A pH/mV meter or an ion meter, either line operated or portable. 2.
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.
Instruction Manual 2. 3. 4. Carbon Dioxide Electrode 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.
Instruction Manual Carbon Dioxide Electrode All samples and standards should be at the same temperature for precise measurement. A difference of 1oC in temperature will result in approximately a 2% error. All samples must be aqueous. Always rinse the electrode with distilled water and blot dry between measurements. Use a clean, dry tissue to prevent cross-contamination. Constant but not violent, stirring is necessary for accurate measurement.
Instruction Manual 10-2 10-3 10-4 Carbon Dioxide Electrode 440.0 44.0 4.4 1,000.0 100.0 10.0 MEASUREMENT PROCEDURE Direct Measurement Direct measurement is a simple procedure for measuring a large number of samples. A single meter reading is all that is required for each sample. The ionic strength of samples and standards should be made the same by adjustment with ISA for all carbon dioxide solutions. The temperature of both sample solutions and standard solutions should be the same.
Instruction Manual Carbon Dioxide Electrode A calibration curve is constructed on semi-logarithmic paper when using the pH/mV meter in the millivolt mode. The measured electrode potential in mV (linear axis) is plotted against the standard concentration (log axis). In the linear region of the curve, only three standards are necessary to determine a calibration curve. In the non-linear region, additional points must be measured.
Instruction Manual Carbon Dioxide Electrode ELECTRODE CHARACTERISTICS Reproducibility Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every hour. Factors like temperature fluctuation, drift, and noise limit reproducibility. Reproducibility is independent of concentration within the electrode's operating range. Interferences Certain volatile weak acids are potential electrode interferences.
Instruction Manual Carbon Dioxide Electrode temperature. Table 3 gives values for the "S" factor in the Nernst equation for the carbon dioxide ion. Gases are expelled from a solution at a faster rate as the temperature increases. TABLE 3: Temperature vs. Values for the Electrode Slope Temp.(oC) 0 5 10 15 20 25 30 35 40 "S" 54.20 55.20 56.18 57.17 58.16 59.16 60.15 61.14 62.
Instruction Manual Carbon Dioxide Electrode Limits of Detection The upper limit of detection in pure carbon dioxide solutions is 1X10-2M. Carbon dioxide is rapidly lost to the air above a concentration of 1X10-2M. Dilution may be used if carbon dioxide concentrations are above 1M. Also dilute samples between 1M and 10-2M or calibrate the electrode at 4 or 5 intermediate points. The lower limit of detection is around 1X10-4M.
Instruction Manual Carbon Dioxide Electrode [H+] [HCO3-] ⎯⎯⎯⎯⎯⎯⎯ = constant [CO2] The bicarbonate ion level can be considered constant since the internal filling solution contains a high level of sodium bicarbonate: [H+] = [CO2] X constant The electrode sensing element's potential, with respect to the internal reference element, varies in a Nernstian manner with changes in the hydrogen level.
Instruction Manual Carbon Dioxide Electrode ELECTRODE APPLICATION Carbon Dioxide Content of Wines and Carbonated Beverages Wines and carbonated beverages have a high (greater than 2X10-2M or 880 ppm) carbon dioxide concentration. As a result, samples are measured after dilution. When samples are collected, they must be made basic immediately or CO2 will escape into the atmosphere (see Sample Storage section). After diluting the sample, it must be acidified with carbon dioxide buffer.
Instruction Manual Carbon Dioxide Electrode Carbonate Content in Groundwater Free CO2, bicarbonate, and carbonate - the total amount of carbonate - in ground water or seawater, will depend on location, temperature, depth, and pH. Using the measurement procedure in the MEASUREMENT section, the carbonate level in groundwater or seawater can be measured. Grab samples taken in the field or ocean can be preserved for laboratory testing by following the procedures given in the Sample Storage section.
Instruction Manual Carbon Dioxide Electrode TABLE 4: Step-wise Calibration for Measurement Step 1 2 3 Pipet A A B Added Volume 0.1 ml 0.9 ml 10.0 ml Concentration 109.9 ppm 1,089 ppm 10,900 ppm A = 1 ml graduated pipet; B = 10 ml volumetric pipet TROUBLESHOOTING GUIDE The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn: the meter, the glassware, the electrodes, the standards, the sample, and the technique.
Instruction Manual Carbon Dioxide Electrode Standards The quality of results depends greatly upon the quality of the standards. ALWAYS prepare fresh standards when problems arise. It could save hours of frustrating troubleshooting! Error may result from contamination of prepared standards, accuracy of dilution, quality of distilled water, or a mathematical error in calculating the concentrations. The best method for preparation of standards is by serial dilution.
Instruction Manual Carbon Dioxide Electrode TROUBLESHOOTING HINTS Symptom Out of Range Reading Noisy or Unstable Reading (readings continuously or random changing.
Instruction Manual Carbon Dioxide Electrode incorrect internal filling solution refill outer body of electrode using filling solution shipped with electrode total sample level dilute sample of dissolved species above 1M electrode in sample too long; CO2 loss reduce surface area-tovolume ratio, slow down rate of stirring, avoid high temperatures membrane failure (wet, perforation, discoloration) replace membrane samples and standards not at constant temperature allow samples and standards to come
Instruction Manual "Incorrect Answer" (but calibration curve is good) Carbon Dioxide Electrode incorrect scaling of semi-log paper plot millivolts on the linear axis.
Instruction Manual Carbon Dioxide Electrode SPECIFICATIONS Concentration Range: 1 x 10-2M to 1 x 10-4M CO2 (440 ppm to 4.4 ppm CO2) pH Range: 4.8 to 5.2 Temperature Range: 0o to 50oC Inner Body Resistance: ~1,000 Mohm Reproducibility: ± 2% Size: 110 mm length; 12 mm diameter; 1 m cable length Storage: Store electrodes in 0.1M NaCl ORDERING INFORMATION CODE NO.
