Thermal and elemental analysis – Fidar Shimi Jam

CHNS/O Elemental Analyzer

admin — Tue, 16 Feb 2021 13:30:33 +0000

High-temperature combustion of a sample in the presence of oxygen has been one of the standard methods of elemental analysis for many years, especially for the determination of carbon, hydrogen, nitrogen, and sulphur in organic compounds. In this method, the sample is broken down by the high temperatures, and these elements come out of the sample. In the presence of oxygen, carbon, hydrogen, nitrogen, and sulfur are converted to CO₂, H₂O, NO_2, and SO₃, respectively. All the combustion and oxidation steps take place inside the CHNS analyzer. Helium is the carrier gas and carries with it the resultant CO₂, water, nitrogen oxides, and sulphur trioxides.

The amounts of CO₂, H₂O, and SO₃ are measured by the infrared detection at their respective absorption wavelengths. The NO₂ content is determined by using thermal conductivity measurement. Before analysis, the device is calibrated with standards with known percentages of carbon, hydrogen, sulphur, and nitrogen to ensure the quantification is accurate.

Differential Scanning Calorimeter (DSC)

admin — Tue, 16 Feb 2021 13:18:18 +0000

Thermogravimetric Analysis (TGA)

admin — Tue, 16 Feb 2021 13:13:39 +0000

In Thermogravimetric Analysis, both sample and reference are given an equal amount of energy. The device measures the difference in the temperature of the sample compared to the reference. If the sample is undergoing an endothermic process (absorbing heat), the temperature decreases, and the slope of the peak on the TGA power as a function of temperature curve is downwards sloping. If the sample is exothermic, then the peak is shifted upward. The area below the peak is the enthalpy change, which is proportional to the specific heat capacity of the material.

Temperature ramp rate has a direct effect on the clarity of the peaks. When the heating is too rapid, not all the transitions can be detected properly, and accuracy is reduced. Modern TGA instruments will have a precision of 0.1 C on the peaks. This technique is applied for isothermal or non-isothermal crystallization studies.