Polarography - Application principles and implementation of polarographic techniques

Polarographic techniques cover a wide range of analytical applications, and can be used in particular in the fields of the environment, water and wastewater analysis, the pharmaceutical, food, cosmetics, oil and nuclear industries, electroplating, biological fluid analysis and the plastics and polymers industry. They are applied to the analysis of main constituents and to trace and ultratrace analysis. They are used for solution analysis of metals, inorganic, organometallic or organic molecules, or molecules of biological and biochemical interest. They enable multi-element analyses and are non-destructive of the solutions analyzed, since the quantities of solutes involved in polarographic measurements are negligible compared with the quantities in solution, thus enabling repetitive measurements on the same solution. They require from a few milliliters to around fifty milliliters of solution, depending on the size of the electrochemical cell used, and can be applied either directly to the sample in the case of a solution, possibly with adaptation of its chemical conditions (addition of an electrolyte carrier, modification of pH, addition of a complexing agent) or concentration adjustment with a dilution step, or after a sample pre-treatment step (filtration, extraction, digestion, oxidation, solubilization, dissolution, purification) for complex or solid matrices, as is the case for many other analytical methods.

In practice, the application of polarographic analysis methods results in the measurement of a current, or sometimes a quantity of charges, at a potential characteristic of the analyte, proportional to its concentration in solution. For quantitative analyses, either a calibration line is established from known concentrations of the solute, to which reference is made for the determination of an unknown concentration, or, to avoid measurement errors due to matrix effects, the dosed addition method is used, whereby additions of known concentrations are made to the solution containing the solute(s) to be analyzed.

The second part of this booklet describes the various polarographic techniques currently in use, explaining how they are implemented, their performance (detection limit, accuracy, repeatability of measurements, selectivity and separating power) and their applications, illustrated by a few practical examples. Classical polarography and pulse polarography techniques using a falling mercury droplet electrode (DME or SMDE) will be discussed, adapted to the concentration range from hundreds of mg · L ^–1 to hundreds of μg · L ^–1 . For trace and ultratrace analysis, anodic and cathodic redissolution methods using a static mercury electrode (HMDE, TFME) will also be...