eutech-instruments cadmium epoxy Manual De Usuario

Cadmium Electrode 

 

Instruction Manual

 

 

6

 
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

               moles/liter 

                1124.0 

 

1.0X10

-2 

                 112.4 

 

1.0X10

-3 

                  11.2 

 

1.0X10

-4

 

 
 
MEASUREMENT PROCEDURE 
 

 
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. The temperature of both sample solutions and of 
standard solutions should be the same. 
 

 

1. 

By serial dilution prepare three standard solutions from the 0.1M, 1,000 ppm or 100 ppm 
standard. The resultant concentrations should be 10

-2

, 10

-3

, and 10

-4

M or 1,000, 100 and 10 

ppm standards. Add 2 ml of ISA to each 100 ml of standard. Prepare standards with a 
composition similar to the samples if the samples have an ionic strength above 0.1M. 

 
2. 

Place 100 ml of the most dilute solution (1.0X10

-4

M or 10 ppm) in a 150 ml beaker on the 

magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the 
mV mode lower the electrode tips into the solution. After the reading has stabilized, record 
the mV reading. 

 
3. 

Place 100 ml of the mid-range solution (1.0X10

-3

M or 100 ppm) in a 150 ml beaker on the 

magnetic stirrer and begin stirring at a constant rate. After rinsing the electrodes with 
distilled water, blot dry and immerse the electrode tips in the solution. After the reading 
has stabilized, record the mV reading. 

 
4. 

Place 100 ml of the most concentrated solution (1.0X10

-2

M or 1,000 ppm) in a 150 ml 

beaker on the magnetic stirrer and begin stirring at a constant rate. After rinsing the 
electrodes with distilled water, blot dry and immerse the electrode tips in the solution.  
After the reading has stabilized, record the mV reading. 

 
5. 

Using the semi-logarithmic graph paper, plot the mV reading (linear axis) against 
concentration (log axis). Extrapolate the curve down to about 1.0X10

-5

 or 1 ppm. A typical 

calibration curve can be found in Figure 1.