User manual EUTECH INSTRUMENTS IODIDE EPOXY

[. . . ] Instruction Manual Iodide Electrode EUTECH INSTRUMENTS PTE LTD. INSTRUCTION MANUAL IODIDE ION ELECTRODE 1 Instruction Manual Iodide Electrode TABLE OF CONTENTS GENERAL INSTRUCTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Required Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Required Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 GENERAL PREPARATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrode Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrode Slope Check (with a pH/mV meter). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Electrode Slope Check (with an ion meter). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 MEASUREMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Measuring Hints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Sample Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Units of Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 MEASUREMENT PROCEDURE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [. . . ] Rinse the electrodes with distilled water and blot dry. 7 2. 3. 4. Instruction Manual Iodide Electrode 5. Place the more concentrated solution on the magnetic stirrer and begin stirring at a constant rate. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions after stabilization of the reading. For low level iodide measurements, place the rinsed, dried electrodes into a solution containing 100 ml of distilled water and 2 ml of ISA. After stabilization, fix the blank value into the meter according to the meter manufacturer's instructions. Place 100 ml of the sample and 2 ml of ISA in a 150 ml beaker, place it on the magnetic stirrer, and begin stirring. Immerse the electrode tips in the solution and wait for the reading to stabilize. Assuming no change in ambient temperature, place the electrode tips in the first iodide standard. After the reading has stabilized, compare it to the original reading in Step 3 above. A reading differing by more than 0. 5 mV or a change in the ambient temperature will necessitate the repetition of steps 2-6 above. The meter should be re-calibrated daily. 6. 7. 8. 9. 10. Low Level Iodide Determinations (using a pH/mV meter) For the iodide electrodes, no special low level determination is necessary. Linear response is possible down to 2. 0X10-8M. ELECTRODE CHARACTERISTICS Reproducibility Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every hour. Factors such as temperature fluctuations, drift, and noise limit reproducibility. Reproducibility is independent of concentration within the electrode's operating range. Interferences A layer of silver may form on the electrode surface in the presence of strong reducing agents. Insoluble salts of silver may be deposited on the membrane, causing electrode malfunction if high levels of ions forming these salts are present in the sample. Solutions containing oxidizing agents such as MnO4-1, Fe+3, and Cu+2, may be measured without problem. The maximum allowable ratio of interfering ion to iodide ion is given in Table 2. This ratio is expressed as the ratio of the interfering ion molarity to the iodide molarity. Neither accuracy of the measurement nor surface of the electrode membrane will be affected if the ratio is less than that listed in the table. 8 Instruction Manual Iodide Electrode TABLE 2: Maximum Allowable Ratio of Interfering Ion to Iodide Ion Interference Cl-1 (1) S2O3-2(2) Br-1 (1) CN-1 (3) S-2 (3) Maximum Ratio 1. 0X106 1. 0X105 5. 0X103 4. 0X10-1 1. 0X10-6 (1) Gran's plot titration can be used to measure mixed halides in solution. (2) These substances represent complexing species whose maximum level can be exceeded without electrode damage. As an example of Table 2's use when using the iodide ion electrode: What is the maximum level of iodide tolerable in a sample whose iodide concentration is 10-4M?Using Table 2, the maximum ratio is: [Br-1] = 5X103 [I-1] or [Br-1] = 5X103 [I -1] = 5X103 (1X10-4) [Br-1] = 5X10-1M maximum bromide concentration for no interference Complexation Total concentration (Ct) consists of free ions (Cf) and complexed or bound ions (Cc) in solutions: Ct = Cf + Cc Since the electrode only responds to free ions, any complexing agent in the solution reduces the measured concentration of ions. TABLE 3: Levels of Complexing Agents Causing a 20% Error at 1. 0X10-4M Iodide Ion Bi+3 Cd+2 Pb+2 Concentration 2. 0X10-5M ( 4 ppm) 5. 0X10-4M ( 50 ppm) 5. 0X10-3M (1, 000 ppm) 9 Instruction Manual Iodide Electrode Temperature Influences Samples and standards should be at the same temperature since electrode potentials are influenced by changes in temperature. [. . . ] The composition of the liquid junction filling solution in the reference electrode is most important. The speed with which the positive and negative ions in the filling solution diffuse into the sample should be equitransferent. No junction potential can result if the rate at which positive and negative charge carried into the sample is equal. Strongly acidic (pH = 0-2) and strongly basic (pH = 12-14) solutions are particularly troublesome to measure. [. . . ]