Simultaneous thermal (TG-DSC) and mass spectrometry analyzes of volatiles in geological materials

• Grant number: 23/17332-8
• Support Opportunities: Research Infrastructure Program - Small Medium Sized
• Start date: September 01, 2024
• End date: August 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Fabio Ramos Dias de Andrade
• Grantee: Fabio Ramos Dias de Andrade
• Host Institution: Instituto de Geociências (IGC). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: Brenda Chung da Rocha ; Colombo Celso Gaeta Tassinari ; Miguel Angelo Stipp Basei ; Renato de Moraes ; Ricardo César Aoki Hirata ; Rogério Guitarrari Azzone ; Valdecir de Assis Janasi

Abstract

Thermal analyzes are used to characterize volatile-bearing materials, including minerals, pharmaceuticals, organic compounds, among others. The principle of analysis is heating the sample at a controlled rate and controlling its mass and enthalpy variations during heating. In mass variation analyzes (TG, thermo-gravimetric), the sample holder is coupled to a precision balance that records the mass variations of the sample during heating, also recording the temperatures at which mass loss events occur. . The classic application in mineralogy is based on the fact that some minerals contain volatiles in their structure (e.g. H2O, OH, C, CO2, S, SOx), in defined proportions and which are released at characteristic temperatures, which allows their identification. Thermodifferential analysis (TD) and its derivative DSC (differential scanning calorimetry), is carried out by measuring the variations in enthalpy or thermal flow between the sample and an inert standard substance. The reactions exhibited by the sample during heating can be endo- or exothermic, which causes the sample to become colder or hotter than the reference material, respectively, during the course of the reaction. Another possible control is the atmosphere of the heating chamber, so that oxidation or reduction reactions are induced or inhibited. The analysis atmosphere is controlled using a flow of gas mixtures.A recent advance in this method was the combination of thermal analyzes with mass spectrometry, which performs real-time chemical analysis of the volatiles emitted by the sample. This evolution of the technique has opened new frontiers for material analysis, allowing the precise identification of volatiles contained in samples.The equipment EMU is a Simultaneous Thermal Analyzer coupled to a mass spectrometer. Currently, only the company Netzsch has equipment with the desired configuration, the STA 449 F5 Jupiter Netzsch model being coupled to the QMS 403 Aëolos Quadro spectrometer. This equipment performs thermal analyzes with heating up to temperatures of 1600 oC at controlled rates. Mass and enthalpy variations are recorded simultaneously, while the chemical compounds in the volatile fraction of the sample are identified by the mass spectrometer. The device is equipped with a high-sensitivity microbalance with a precision of 0.1 microgram, and allows analyzing samples between 5 mg and 35 g. The system heats the sample in a static, dynamic, inert or oxidizing atmosphere, with the system atmosphere being controlled by a mixture of gases. Vacuum pump and gas adapters come with the set. Heating rates are adjustable between 0.001 and 50 K/min. The system is controlled by a computer with calibration and control software, for data acquisition and processing in a Windows environment (Proteus basic software, ExpertMode user interface), both for thermal and mass spectrometry analyses. It comes with a set of seven pure substances for enthalpy and temperature calibration (In, Sn, Zn, Al, Ag, Au, Ni) in Al2O3 sample holders, and a set of sapphire discs of certified purity for enthalpy calibration. (AU)