Preconcentration of poorly volatile impurities in thin-layer chromatography by thermodesorption of a volatile matrix

A method for preconcentration of poorly volatile impurities by continuous thermodesorption of the major component on a TLC plate is proposed. The method provides multiple (200–500) concentration of the organic impurities present in the initial solution. A simple device for such concentration is suggested. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2075–2076, October, 1998.     

The Studies of the Heterogeneous Properties of Solid Surfaces by Means of the Derivatograph Q-1500 D

A simple method has been adopted to obtain an important information on the heterogeneous properties of materials studied, adsorbed liquid films and liquid-solid interactions. The method utilizes Q-TG mass loss and the first derivative Q-DTG mass loss curves with respect to temperature and time obtained during programmed liquid thermodesorption in quasi-isothermal conditions. The values of the adsorption capacity, total porosity of material, the value of active centers, desorption energy distribution and mesopore-size distribution functions obtained by this method are in good agreement with those estimated on the basis of independent methods. The theoretical and experimental results provided novel and unique data on the heterogeneity of solid surfaces, properties of liquid adsorbed films and thermal stability of the liquid/solid interfaces. This paper presents the more important results obtained so far in the studies the liquid/solid systems by means of the Paulik's classical and quasi-isothermal techniques. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measurements Of Biogenic Hydrocarbons And Their Atmospheric Degradation In Forests

Abstract

An analytical procedure for the sampling and quantitative determination of biogenic hydrocarbons in the atmosphere is presented. The method is based on the adsorptive preconcentration of the hydrocarbons using Tenax TA/Carbopack B filled sampling tubes followed by thermodesorption of the trapped compounds and gas chromatographic analysis. To avoid losses of the biogenic alkenes as a consequence of their reaction with ozone on the adsorbents during the sampling step, an ozone scrubber is used in front of the adsorption tubes. Diurnal variations of the monoterpene- and ozone-concentrations are determined at different heights in and above a forest stand (coniferous and deciduous trees) in the Vosges (Col du Donon, 760 m a.s.l.) in order to elucidate the importance of terpene-oxidation reactions on the formation of peroxidic products in forest air.     

Study of Heterogeneous Properties of Solids by Means of a Special Thermal Analysis Technique

Thermogravimetry (TG) was successfully applied in order to study the heterogeneous properties of solid surfaces and adsorbed liquid films. The method utilized the thermogravimetric mass-loss Q-TG and differential Q-DTG curves with respect to temperature and time for the desorption of liquidus from solid surfaces under quasi-isothermal conditions. Evaluation of the experimental data revealed the heterogeneous properties of the tested samples. It appears that this modern special TG technique is very useful for the study of liquid/solid systems and can be competitive with traditional techniques because of the speed and accuracy with which the data are obtained and the simplicity of the experimental operations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodesorption studies of ammonium nitrate prills by high-resolution thermogravimetry

High-resolution thermogravimetry was used to study the thermodesorption of octane from ammonium nitrate (AN) prills with different porosities. The samples were wetted by immersion in octane. Multiple steps were obtained from the measured mass-loss curves, which reflect the evaporation of the excess liquid, as well as the thermodesorption of octane from the pores and the surface of the AN prills. The quantity of octane desorbed in these steps was correlated with the volume in the pores and the amount adsorbed on the surface, and used to estimate the adsorption capacity, porosity and surface area of AN prills. The results were also compared to observations from scanning electron microscopy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Application of CRTA to the study of microporosity by thermodesorption of pre-adsorbed water

Thermodesorption is here considered for its possibility of giving access to the microporosity of adsorbents. The requirements of this application (good separation of successive desorption steps, good control of the desorption pressure and temperature throughout the sample, possibility of a safe kinetic analysis of each step) are here fulfilled by carrying out the thermodesorption in the Controlled transformation Rate Thermal Analysis (CRTA) mode. The method is applied to 4 zeolites (3A, 4A, 5A and 13X) and a well characterized charcoal, from ?25 to 325°C, after pre-adsorption of water.     

Studies on Water and Ammonia Programmed Thermodesorption of Mixed M(III)-vanadyl Phosphates

Hydrated M(III)-vanadyl phosphates (M (III)=Mn, Fe, Ga, Al) have been prepared and studied for water and ammonia adsorption properties by TG/DTA, NH₃ TPD, FTIR and XRD techniques. The compounds have the same tetragonal layered structure of VOPO₄ ⋅2H₂ O, but shorter interlayer distances. Ammonia adsorption leads to intercalation of large amounts (0.19–0.39 mol/mol) of base between the layers of the materials, without displacement of water. The ammoniated phases obtained from these compounds have interlayer distances shorter than that of the corresponding precursors. In this connection an interaction mechanism NH₃ -host is proposed. Treated at 450°C the materials adsorb ammonia only on the external surface because of the large decrease of the interlayer distance that prevents NH₃ from entering the interlayer space. All M(III)-vanadyl phosphates present a wide distribution of strength of ammonia adsorbing sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Aluminium Oxide Samples by Means of Special Thermal Analysis Techniques

Thermodesorption of benzene and water from alumina samples saturated in vacuum dessicator were studied under quasi-isothermal conditions. The Q-TG and Q-DTG curves show multi-step mass losses associated with the evaporation of liquids from pores and physisorbed liquid films from active sites with different energies. The isotherms of adsorption-desorption of nitrogen on porous alumina samples were measured using sorptomatic method and pore size distribution functions have been calculated. The correlation between porosity parameters and the volume of desorbed liquids is presented. A good agreement between above data was obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sample enrichment in high speed narrow bore capillary gas chromatography

Reduction of the column diameter has proved to be a highly efficient tool to increase the speed of analysis. Unfortunately, the requirements for instrumental design with respect to sample input band width, low dead volume interfacing, and time constants of detection and registration systems are the more critical the smaller the inside diameter. Recently we reported input band widths as low as 1 ms [1] for gaseous samples at ppm concentration levels, without any preconcentration, in a study with narrow bore columns and thermal conductivity detection. In this study a simple versatile micro on-column cold trap/thermodesorption enrichment system for narrow bore columns is introduced and evaluated. The combination of considerable sample enrichment and preservation of the compatibility of the required input band width with column dimensions is critically examined. The process of thermodesorption (reinjection) which is the most critical step, is particularly emphasized. The system consists of a short aluminum coated fused silica or metal capillary with a low mass and a low cost electrical heating. Input band widths down to 1 ms are obtained without extreme demands on electrical power (300 watt). The potential of the system is illustrated with some extremely fast separations.