This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.
Operation method
Experimental determination of lead by oscillometric polarography
Principle
The principle of single-scan oscillographic spectroscopy is basically similar to that of ordinary spectroscopy, which is to apply a voltage that changes in a straight line from time to time to the two electrodes of the electrolytic cell containing the ions to be measured (known as the scanning voltage), and to display the current and voltage curves on the fluorescent screen of the oscilloscope. The difference is that single-scan oscillometric polarography is a drop of mercury is scanned at a rate of 0.25 V-S-1 at the late stage of growth, and because the rate of scanning is very fast (ordinary polarography is generally 0.2 V-min-1), when the decomposition voltage of a reducible substance is reached, the substance is rapidly reduced at the electrodes, and a very large current is generated. Since the concentration of the reducible substance in the vicinity of the electrode decreases sharply, and the reducible substance in the solution body is too late to diffuse to the electrode, the current decreases rapidly until the electrode reaction rate and diffusion rate reach equilibrium. The polarographic curve of the oscillometric polarography thus takes the shape of a sharp peak. For the reversible electrode reaction, the relationship between the peak current ip and reducible substances can be expressed in the following formula for the mercury drop electrode: where tp is the growth of mercury droplets to the peak of the time (s); V is the scanning speed (V-S-1), and the other with the Ilkovic equation. It can be seen that the peak current is proportional to the concentration of the depolarizing agent when other conditions are the same, which is the basis for quantitative analysis. In this experiment, Pb2+ was determined by single sweep oscillometric method in tartaric acid, KI substrate. In the presence of KI, Pb2+ forms complex ions with I-, which are adsorbed on the electrode and then reversibly reduced to form a sensitive complex adsorbate with a peak potential of -0.59V (for S.C.E.) nearby. This method is suitable for the determination of lead in human hair, mineral samples and some chemical reagents.
Materials and Instruments
1% Ascorbic Acid Solution 10% Tartaric Acid Solution 10% Potassium Iodide Solution Lead Standard Solution Move Tune up the oscillometric polarimeter. For more product details, please visit Aladdin Scientific website.
JP-2 Oscillometric Polarimeter
In seven 10 mL volumetric flasks, add 1.0 mL of 10% tartaric acid, 0.3 mL of 1% ascorbic acid, 0.5 mL of 10% KI solution, and then add 0, 0.1, 0.2, 0.4, 0.6, 0.8 mL of 50 μg / mL of lead solution, dilute it with water to the scale, and then shake well. From low concentration to high concentration for the oscillogram, note down the height of the peak current.
Take 5.0 mL of water sample, add tartaric acid and other reagents as above, and finally dilute with water to the scale, shake well. Make an oscillogram under the same conditions as above and note down the peak height.