CHEMISTRY 425

Instrumental Methods of Analysis

ANODIC STRIPPING ANALYSIS

APPARATUS: Hanging Hg drop electrode, Pt counter electrode, saturated calomel reference electrode, ramp generator and stop generator.

Nitrogen tank (oxygen-free)

Timer, stirrer

SOLUTIONS: 0.1 mol/l KC1

1.000 x 10-4 mol/l Cd+2

PROCEDURE: Clean all glassware to be used with nitric acid to remove cations absorbed on the glass.

Parameter Study: Record current potential curves for the following instrument settings using a solution which is 5 x 10-6 mol/l Cd+2 and 0.1 mol/l KC1:

Drop Size Electrolysis Electrolysis Scan Rate,

(# of drops) time, min potential, V mV/min

2 2.50 -0.750 100

2 2.00 -0.750 100

1 2.50 -0.750 100

2 2.50 -1.000 100

2 2.50 -0.750 200

Analysis of Cadmium: Prepare the following standard solutions in 100 ml volumetric flasks. Record a current-potential curve for each solution using optimum parameters determined above. Repeat (if time permits) to obtain duplicate results for each solution.

Solution # mol/l Cd+2 mol/l KC1

1 0 0.1

2 1 x 10-6 0.1

3 2 x 10-6 0.1

4 5 x 10-6 0.1

5 unknown 0.1

Treatment of data: Prepare a calibration curve, by plotting concentration vs. peak current and determine the concentration of your unknown.

QUESTIONS: 1. How do the parameters examined affect the data obtained and why? (i.e. discuss drop size, time, step potential, and scan rate.)

2. If duplicate results were obtained, were the results within 3-5% of each other? If not, why?

3. At what potential does the peak occur? Does it agree with the literature value? Is it the same for all concentrations of cadmium?

4. How does this experiment compare to normal polarography in terms of accuracy and detection limits?

PVKAH