Exeter Analytical has developed an analytical method for determining the percentage Carbon (C), Hydrogen (H) and Nitrogen (N) content of polyfluorinated compounds (PFCs)
Due to their specific technical characteristics, polyfluorinated compounds are used in a number of products such as in textiles, carpets, cosmetics, paper, packaging materials as well as in general in the chemical synthesis.
Generally compounds containing fluorine can be successfully analysed for percentage CHN content on an elemental microanalysis system under standard operating conditions.
However, polyfluorinated samples, which are often difficult to combust, can give incorrect low carbon and high nitrogen data.
For these highly fluorinated compounds, Exeter Analytical have developed a new analytical method based upon their Model 440 Elemental Analyser.
The CE440 Elemental Analyser offers a horizontal design, enabling sample ash removal between each analysis.
According to the company, this eliminates any potential memory effects and ensures consistent high quality.
The samples to be analysed are weighed into disposable tin or aluminum capsules and are then injected into a high temperature furnace and combusted in pure oxygen.
The resulting combustion products pass through specialised reagents to produce from the elemental carbon, hydrogen, and nitrogen; carbon dioxide (CO2), water (H2O) and nitrogen (N2) and N oxides.
These reagents also remove all other interferences including halogens, sulfur, and phosphorous.
The gases are then passed over pure copper wire to remove excess oxygen and to reduce oxides of nitrogen to elemental nitrogen.
After this stage the gases enter a mixing chamber to ensure a homogeneous mixture at constant temperature and pressure.
The mixture then passes through a series of high-precision thermal conductivity detectors, each containing a pair of thermal conductivity cells.
Between the first two cells is a water trap.
The differential signal between the cells is proportional to the water concentration, which is a function of the amount of hydrogen in the original sample.
Between the next two cells is a carbon dioxide trap for measuring carbon.
Nitrogen is measured against a helium reference.
Sulfur is measured separately, as sulfur dioxide, by replacing the combustion and reduction reagents.
Oxygen is also measured separately by pyrolysis in the presence of platinised carbon.
The oxygen is finally measured as carbon dioxide.
