Ionization was performed under electrospray conditions (flow rate 1.0 μL/min, spray voltage 4.8 kV, sheath gas 40 arb). All spectra were acquired at a capillary temperature of 25°C, and all ion guide voltages were tuned to maximize the abundance of the total ion current. The analyte solutions (250 pmol/μL) were prepared in methanol. Methanol was of HPLC grade (Sigma, St. Louis, MO, USA). Fourier transform infrared spectroscopy FTIR spectra were recorded using a FT IR CB-839 supplier NEXUS
spectrometer (Thermo Fisher Scientific Inc., Madison, WI, USA) at room temperature in the frequency range of 4,000 to 400 сm−1 in diffuse reflection mode at a resolution of 4 сm−1, a scan rate of 0.5 сm/s and number of scans of 150. In diffuse reflectance mode, the powdered samples were mixed with freshly calcined and milled KBr (1:100). Method of temperature-programmed desorption mass spectrometry TPD-MS experiments were performed in a MKh-7304A monopole mass spectrometer (Electron, Sumy, Ukraine)
with electron impact ionization, adapted for thermodesorption measurements. A typical test comprised placing a 20-mg sample on the bottom of a molybdenum-quartz ampoule, evacuating to approximately 5 × 10−5 Pa at approximately 20°C and then heating at 0.15°C/s from room temperature to approximately 750°C. For all the samples, the sample vials were filled approximately 1/16 full, which helped limit interparticle diffusion effects PF-562271 purchase [24–28]. Limiting the sample volume along with the high vacuum should further limit readsorption and diffusion resistance as described elsewhere [24–33]. The LB-100 mw volatile pyrolysis products was passed through a high-vacuum
valve (5.4 mm in diameter, a length of 20 cm and a volume of 12 mL) into the ionization chamber of the mass spectrometer where they were ionized and fragmented by electron impact. After mass separation in the mass analyzer, the ion current due to desorption and pyrolysis was amplified with a VEU-6 secondary-electron multiplier (“”Gran”" Federal State Unitary Enterprise, Vladikavkaz, Galeterone Russia). The mass spectra and the P-T curves (where P is the pressure of volatile pyrolysis products, and T is the temperature of the samples) were recorded and analyzed using a computer-based data acquisition and processing setup. The mass spectra were recorded within 1 to 210 amu. During each TPD-MS experiment, approximately 240 mass spectra were recorded and averaged. During the thermodesorption experiment, the samples were heated slowly while keeping a high rate of evacuation of the volatile pyrolysis products. The diffusion effects can thus be neglected, and the intensity of the ion current can be considered proportional to the desorption rate.