EUTECH INSTRUMENTS PTE LTD.
TABLE OF CONTENTS GENERAL INSTRUCTIONS .......................................................................................................... 1 Introduction ..............................................................................................................................................2 Required Equipment.................................................................................................................................2 Required Solutions .......................................
Instruction Manual Lead Electrode GENERAL INSTRUCTIONS ............................................................ Error! Bookmark not defined. Introduction ............................................................................................................Error! Bookmark not defined. Required Equipment...............................................................................................Error! Bookmark not defined. Required Solutions ......................................................
EUTECH INSTRUMENTS PTE LTD. LEAD ION ELECTRODE INSTRUCTION MANUAL GENERAL INSTRUCTIONS Introduction Eutech Instruments Lead Ion Electrode is used to measure lead or sulfate ions in aqueous solutions quickly, simply, accurately, and economically. Required Equipment 1. A pH/mV meter or an ion meter, either line operated or portable. 2. Semi-logarithmic 4-cycle graph paper for preparing calibration curves when using the meter in the mV mode.
Instruction Manual Lead Electrode Pb(ClO4)2·3H2O. Swirl the flask gently to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend several times to thoroughly mix the solution. 5. Eutech Lead Perchlorate Standard, 1,000 ppm Pb(ClO4)2, Code no. EC-SCS-PB2-BT. To prepare this solution from your own laboratory stock, half fill a one liter volumetric flask with distilled water and add 2.30 grams of reagent-grade lead perchlorate, Pb(ClO4)2·3H2O.
3. Adjust the meter to the concentration of the standard and fix the value in the memory according to the meter manufacturer's instructions. 4. Rinse the electrodes with distilled water and blot dry. 5. To another 150 ml beaker, add 50 ml of methanol-formaldehyde solution and 50 ml of the higher value standard. Add 2 ml of ISA. Place the beaker on a magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution. 6.
Instruction Manual Lead Electrode The temperature of the standard solutions and of the sample solutions should be the same and below 80oC. About a 4% error in the slope will occur for each 1oC difference in temperature. Interferences should be absent. If they are present, use the procedure found in the Interferences and Electrode Response sections to remove them. Units of Measurement Lead concentrations are measured in units of ppm as lead, moles per liter, or any other convenient concentration unit.
5. Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against the concentration (log axis). Extrapolate the calibration curve down to about 2.0X10-6M. A typical calibration curve can be found in Figure 1. A calibration curve is constructed on semi-logarithmic paper when using a pH/mV meter in the millivolt mode. The measured electrode potential in mV (linear axis) is plotted against the standard concentration (log axis).
Instruction Manual Lead Electrode Direct Measurement of Lead (using an ion meter) 1. 2. By serial dilution of the 0.1M or l,000 ppm lead standard, prepare two lead standards whose concentration is near the expected sample concentration. Measure out 50 ml of each standard into individual 150 ml beakers. Add 50 ml of methanol-formaldehyde solution and 2 ml of ISA to each beaker. Place the more dilute solution on the magnetic stirrer and begin stirring at a constant rate.
Low Level Lead Determination (using a pH/mV meter) This procedure is recommended for solutions with lead concentrations of less than 1.0X10-6M. If the solution is high in ionic strength, but low in lead ion concentration, use the same procedure, but prepare a calibration solution with a composition similar to the sample. 1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level ISA (1.0M NaClO4) is added at the rate of 1 ml low level ISA to each 100 ml of solution.
Instruction Manual Lead Electrode reading has stabilized, record the mV reading and determine the concentration from the low level calibration curve. Prepare a new low level calibration curve daily. Check the calibration curve every two hours by repeating Steps 3- 7 above. Low Level Lead Determination (using an ion meter) 1. Using 20 ml of standard ISA, dilute to 100 ml with distilled water. This low level (1.0M NaClO4) is added at a the rate of 1 ml low level ISA to each 100 ml of solution.
Titration Titration is a very accurate determination of total lead or sulfate ion concentration. This method makes use of the electrode as an endpoint detector. The endpoint break is enhanced by the use of methanol-formaldehyde solution added to samples to reduce the solubility of the product formed during titration. Titration of Lead The method outlined in this section makes use of the lead ion electrode as a highly sensitive endpoint detector for lead-containing sample. The titrant used is EDTA.
Instruction Manual Lead Electrode Titration of Sulfate Titration of sulfate ion with lead perchlorate make use of the lead ion electrode as a sensitive endpoint detector. Sulfate determinations by the gravimetric or turbidimetric methods are more complicated and more time consuming than titration. Titration offers the same or greater precision in solutions as dilute as 10-4M or 10 ppm sulfate ion.
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Instruction Manual Lead Electrode ELECTRODE CHARACTERISTICS Reproducibility Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated frequently. Factors such as temperature fluctuations, drift, and noise limit reproducibility. Reproducibility is independent of concentration within the electrode's operating range. Interferences A surface layer of silver metal may be formed by strongly reducing solutions.
30 40 50 30.07 31.07 32.06 If changes in temperature occur, the electrodes should be re-calibrated. The temperature range for the Eutech Lead Ion Electrode is 0o-80oC, provided that temperature equilibrium has occurred. If the temperature varies substantially from room temperature, equilibrium times up to one hour are recommended.
Instruction Manual Lead Electrode The lower limit of detection is influenced by the slight water solubility of the electrode pellet. Refer to Figure 1 for a comparison of the theoretical response to the actual response at low levels of lead ion. Neutral solutions containing free lead ions can be measured down to 1.0X10-6M (0.2 ppm). Extreme care must be taken with measurements below 1.0X10-5M (2.0 ppm) to avoid adsorption of lead ions in the sample onto container walls.
The activity, X, represents the effective concentration of free lead ion in the solution. Both bound, Cb, and free, Cf, lead ions are included in the total lead ion concentration, Ct.
Instruction Manual Lead Electrode TROUBLESHOOTING GUIDE The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn: the meter, the glass-ware, the electrodes, the standards and reagents, the sample, and the technique. Meter The meter may be checked by following the check-out procedure in the instrument instruction manual. Glass-ware/Plastic-ware Clean glass-ware is essential for good measurement.
Technique Be sure that the electrode's limit of detection has not been exceeded. Be sure that the analysis method is clearly understood and is compatible with the sample. Refer to the instruction manual again. Reread sections on GENERAL PREPARATION and ELECTRODE CHARACTERISTICS. If trouble still persists, call Eutech Instruments Pte Ltd. at (65) 6778-6876 ask for the Customer Services Department.
Instruction Manual Lead Electrode TROUBLESHOOTING HINTS Symptom Out of Range Reading Possible Causes defective meter Next Step check meter with shorting strap (see meter instruction manual) defective electrode check electrode operation electrodes not plugged in properly unplug electrodes and reset reference electrode not filled be sure reference electrode is filled air bubble on membrane remove bubble by re-dipping electrode electrodes not in solution put electrodes in solution Noisy or defec
Low Slope or No Slope "Incorrect Answer" (but calibration curve is good) standards contaminated or incorrectly made prepare fresh standards standard used as ISA use ISA ISA not used use recommended ISA membrane dirty or oxidized polish membrane; use methanol-formaldehyde solution air bubble on membrane remove bubble by re-dipping probe incorrect scaling of semi-log paper plot millivolts on the linear axis.
Instruction Manual Lead Electrode SPECIFICATIONS Concentration Range: 10-1M to 10-6M Pb+2 (20,700 to 0.2 ppm Pb+2) pH Range: 3 to 8 Temperature Range: 0o - 80oC Resistance: < 1 Mohm Reproducibility: +/- 2% Samples: Aqueous solutions only; no organic solvents Size: 110 mm length; 12 mm diameter; 1 m cable length Storage: Store in lead solution ORDERING INFORMATION CODE NO. DESCRIPTION EC-PB-03 Lead Ion Electrode, epoxy body combination, EC-SCS-PB1-BT Lead Standard, 0.
