Instruction Manual Cadmium Electrode EUTECH INSTRUMENTS PTE LTD.
Cadmium Electrode Instruction Manual TABLE OF CONTENTS GENERAL INSTRUCTIONS .......................................................................................................... 3 Introduction.................................................................................................................................................3 Required Equipment ...................................................................................................................................
Instruction Manual Cadmium Electrode EUTECH INSTRUMENTS PTE LTD CADMIUM ION ELECTRODE INSTRUCTION MANUAL GENERAL INSTRUCTIONS Introduction Eutech Instruments Cadmium Ion Electrode is used to measure cadmium 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. 3. A magnetic stirrer.
Cadmium Electrode Instruction Manual dissolve the solid. Fill to the mark with distilled water, cap, and upend several times to mix the solution. GENERAL PREPARATION Electrode Preparation Remove the rubber caps covering the electrode tips and the rubber insert covering the filling hole of the cadmium combination electrode or the reference electrode. Fill the reference electrode or the combination electrode with the filling solution shipped with the electrode to a level just below the fill hole.
Instruction Manual Cadmium Electrode 5. To a 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution. 6. Adjust the meter to the concentration of the standard and fix the value in the memory. 7. Read the electrode slope according to the meter manufacturer's instructions. Correct electrode operation is indicated by a slope of 90-100%.
Cadmium Electrode Instruction Manual Units of Measurement Cadmium ion concentrations are measured in units of parts per million, moles per liter, equivalents per liter, or any other convenient concentration unit. Table 1 indicates some of these concentration units. TABLE 1: Concentration Unit Conversion Factors ppm Cd+2 1124.0 112.4 11.2 moles/liter 1.0X10-2 1.0X10-3 1.0X10-4 MEASUREMENT PROCEDURE Direct Measurement Direct measurement is a simple procedure for measuring a large number of samples.
Instruction Manual Cadmium Electrode 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). 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. The direct measurement procedures given are for the linear portion of the curve.
Cadmium Electrode Instruction Manual 3. Adjust the meter to the concentration of the cadmium standard and fix the value in the memory according to the meter manufacturer's instructions after stabilization of the reading. 4. Rinse the electrodes with distilled water and blot dry. 5. Place the more concentrated solution on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the solution 6.
Instruction Manual Step 1 2 3 4 5 6 7 Cadmium Electrode Pipet A A A A A B B Added Volume (ml) 0.1 0.1 0.2 0.2 0.4 2.0 2.0 Concentration ppm M 0.01 1.0X10-7 0.02 2.0X10-7 0.04 4.0X10-7 0.06 6.0X10-7 0.10 9.9X10-7 0.29 2.9X10-6 0.48 4.8X10-6 Pipet A = 1 ml graduated pipet Pipet B = 2 ml pipet Solutions: additions of 10 ppm or 1.0X10-4M standard to 100 ml of solution prepared in Step 3 above. 7.
Cadmium Electrode Instruction Manual Titration of Cadmium The method outlined in this section makes use of the cadmium ion electrode as a highly sensitive endpoint detector for cadmium-containing samples. The titrant used is EDTA. EDTA complexes cadmium as well as other cations. The sample pH can be adjusted to pH 10 by adding ammonia to eliminate unwanted ion complexes. Masking agents may be added in some cases. 1. Prepare the stock EDTA titrant as given in the section Required Solutions.
Instruction Manual Cadmium Electrode MCd+2 = ———— VCd+2 where: MCd+2 = concentration of cadmium ion in the sample (moles/liter) Vt = volume of EDTA added at endpoint Mt = EDTA concentration (moles/liter) +2 Cd = volume of unknown sample (100 ml) ELECTRODE CHARACTERISTICS Reproducibility Electrode measurements reproducible to ±2% can be obtained if the electrode is calibrated every hour. Factors like temperature fluctuations, drift, and noise limit reproducibility.
Cadmium Electrode Instruction Manual Temperature Influences Samples and standards should be at the same temperature, since the electrode potentials are influenced by changes in temperature. A 1oC difference in temperature results in a 4% error at the 1.0X10-3M cadmium concentration. Because of the solubility equilibrium on which the electrode depends, the absolute potential of the reference electrode changes slowly with temperature.
Instruction Manual Cadmium Electrode A drifting potential reading or a decrease in electrode slope may mean that the electrode membrane needs polishing. To polish the membrane: 1. If using polishing paper, cut off a 1-2" piece and place it face up on the lab bench. 2. Put a few drops of distilled or deionized water in the center of the paper. 3.
Cadmium Electrode Instruction Manual interference from hydroxide is given by a dashed line to the left of the dotted area on Figure 4. Within this dotted area, cadmium combines with hydroxide to form Cd(OH)2. Since only free cadmium concentration can be measured with the cadmium ion electrodes, a false reading results. Electrode Life A cadmium electrode will last six months in normal laboratory use. On-line measurements might shorten operational lifetime to several months.
Instruction Manual Cadmium Electrode where: Cx = concentration of ion X Zx = charge of ion X Σ = sum of all the types of ions in the solution In the case of high and constant ionic strength relative to the sensed ion concentration, the activity coefficient, γ, is constant and the activity, X, is directly proportional to the concentration. To adjust the background ionic strength to a high and constant value, ionic strength adjuster is added to samples and standards.
Cadmium Electrode Instruction Manual 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 and reagents, the sample, and the technique. Meter The meter may be checked by following the check-out procedure in instrument instruction manual. Glass-ware Clean glass-ware is essential for good measurement.
Instruction Manual Cadmium Electrode Sample Look for possible interferences, complexing agents, or substances which could affect the response or physically damage the sensing electrode (or reference electrode) if the electrodes work perfectly in the standard, but not in the sample. Try to determine the composition of the samples prior to testing to eliminate a problem before it starts. (See Measuring Hints, Sample Requirements, and Interferences.
Cadmium Electrode Instruction Manual TROUBLESHOOTING HINTS Symptom Out of Range Reading Noisy or Unstable Readings (readings continuously or rapidly changing) Drift (reading slowly changing in one direction) 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 bubb
Instruction Manual Low Slope or No Slope Cadmium Electrode incorrect reference filling solution use recommended filling solution standards contaminated or incorrectly made prepare fresh standards ISA not used use recommended ISA standard used as ISA use ISA electrode exposed to complexing agents check section entitled Precipitation and Complexation "Incorrect Answer" (but calibration curve is good) air bubble on membrane remove bubble by redipping probe incorrect scaling of semi-log paper p
Cadmium Electrode Instruction Manual SPECIFICATIONS Concentration Range: 1.0X10-1M to 1.0X10-7M (11,200 to 0.01 ppm) pH Range: 2 to 12 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 cadmium solution ORDERING INFORMATION CODE/NO.
