Thermal analytical procedures

The performance of powder coatings during fusion and subsequent cure may be followed in detail by thermal analytical procedures such as differential thermal analysis and differential scanning calorimetry. These techniques offer an opportunity for the study of phase transitions and cure behaviour under closely controlled conditions. Differential scanning calorimetry is a requirement in the British Gas standard for epoxy powder coating materials for the external coatings of steel pipes where it is used as a guide to ascertain optimum cure conditions. 

Thermogravimetiy (TG) is one of the oldest thermal analytical procedures and has been used extensively to study pyrolysis, combustion, and gasification of coal, coke, and polymers. The technique involves monitoring the weight loss of a sample in a chosen atmosphere as a function of temperature, whereby the heating rate is kept constant. The usefulness of TG for analyzing kinetic... 

Ozone can be analyzed by titrimetry, direct and colorimetric spectrometry, amperometry, oxidation—reduction potential (ORP), chemiluminescence, calorimetry, thermal conductivity, and isothermal pressure change on decomposition. The last three methods ate not frequently employed. Proper measurement of ozone in water requites an awareness of its reactivity, instabiUty, volatility, and the potential effect of interfering substances. To eliminate interferences, ozone sometimes is sparged out of solution by using an inert gas for analysis in the gas phase or on reabsorption in a clean solution. Historically, the most common analytical procedure has been the iodometric method in which gaseous ozone is absorbed by aqueous KI. 

Analytical procedures sensitive to 2 ppm for styrene and 0.05 ppm or less for other items were used for examining the extracts. Even under these exaggerated exposure conditions no detectable levels of the monomers, of the polymer, or of other potential residuals were observed. The materials are truly non-food-additive by the FDA definitions. Hydrogen cyanide was included in the list of substances for analysis since it can be present at low levels in commercial acrylonitrile monomer, and it has been reported as a thermal decomposition product of acrylonitrile polymers. As shown here, it is not detectable in extracts by tests sensitive to... 

However, pyrolysis is rapid, avoids sample wet chemical workup, avoiding sample loss and contamination, and has a low sample requirement. It allows the determination, in a single step, of polymeric materials (with in situ hydrolysis of the hydrolysable polymers and thermal decomposition of the nonhydrolysable polymers) and low molecular weight components [16]. As a result, pyrolysis is a relatively fast and inexpensive technique, especially if compared with the classical wet analytical procedures that are required prior to GC/MS analyses. 

Certain volatile elements must be analyzed by special analytical procedures as irreproducible losses may occur during sample preparation and atomization. Arsenic, antimony, selenium, and tellurium are determined via the generation of their covalent hydrides by reaction with sodium borohydride. The resulting volatile hydrides are trapped in a liquid nitrogen trap and then passed into an electrically heated silica tube. This tube thermally decomposes these compounds into atoms that can be quantified by AAS. Mercury is determined via the cold-vapor... 

The degree of hydration of the products from these preparations and the water content given by analytical procedures depends upon the heat treatment (method and history) of the product. A sample subjected to TGA (thermal gravimetric analysis) looses water almost continually from room temperature until it becomes the completely anhydrous heteropolytungstate salt at about 400°C. On the other hand, these crystals lose some lattice water rapidly upon removal from the mother liquor and exposure to air even at room temperature. 

Two compns ate as follows a)CCl NC(12.6% N) 37.5, RDX 50.0, butylstearate 12.0 DPhA 0.5 and b)CC2 NC(12.6% N) 36.5, RDX 53.0, butylstearate 10,0 DPhA 0.5% About 0.4% of K nitrate could be added as flash-reducer. The proplnt CC2 was intended for use in high-velocity weapons, such as 90mm AT and T guns. The CC proplnts exhibited superior thermochemical props, showed good velocity relationship and better thermal stability than proplnts contg NG. Their disadvantage was poor uniformity from round to round. The manuf and analytical procedures are described in Ref 2(See also CR Propellants)... 

Isotope ratios provide insight into the physical and chemical processes that cause alteration of their values. Their application is expanding as analytical procedures become more sophisticated and sensitive, and as the extent of scientific knowledge increases. As in many fields, much work done today would have been impossible a few years ago. With the advent of multicollector inductively coupled plasma (ICP) mass spectrometers, it is probable that routine use of thermal ionization will diminish, but it seems that it will always play a role in applications in which utmost sensitivity is required. 

Brine waste represents the largest waste stream at baseline incineration sites. The total volume is estimated to be as much as 24,000 tons per year at ANCDF, PBCDF, and TOCDF.19 At UMCDF, a thermal evaporation brine reduction process is used to concentrate the brine solution to brine salts before disposal. Analytical procedures exist for the characterization of brine solutions and brine salt waste. The procedures are detailed in the waste analysis plan for each site. Most brine waste streams, either liquid or salt, are characterized and shipped off-site for disposal at a permitted TSDF. Therefore, while brine waste is a large stream, readily available off-site disposal options exist for both the spent brine solutions and the brine salts. No brine waste exists at NECDF. 

Whilst gas chromatography has been used for the analysis of many of the lycoctonine-based alkaloids [52], the larger, less volatile, and more thermally labile MSAL compounds require analytical procedures such as TLC and HPLC for separation and detection. For example, both normal phase liquid chromatography [53] and reversed phase liquid chromatography [54] with UV detection have been used for separation, detection, and quantitation of alkaloids from Delphinium species associated with livestock poisonings in the western US and Canada. The introduction of API techniques has allowed the analysis of all types of diterpene alkaloids by direct MS methods and with MS methods coupled to liquid chromatography. 

The requirements for chemical actinometers, listed in the previous sections [such as sensitivity, reproducibility, (thermal) stability, ease of analytical procedure, etc.], reduce the seemingly unlimited number of actinometers reported over the years (9) to a short list of well-established and highly recommended chemical actinometers. In this section, we first present a selected list of such reliable actinometers, which all operate in the liquid phase. After that, a few controversial systems are described and their potential error sources discussed. Finally, actinometric procedures suitable for solid-state applications, polychromatic sources, and laser irradiation will be introduced in section "Special Applications."... 

The MP-3 Thermal Chromatograph (Spex Industries, Inc., Me-tuchen, NJ) facilitates the slow (up to 40°C/min) controlled atmosphere pyrolysis of solid oil shale. The volatile compounds produced are monitored by both flame ionization and thermal conductivity detectors and after trapping, the whole or portions of the evolved organic proflle may be further subjected to GC and other analytical procedures. In contrast, the CDS 100 pyroprobe and associated CDS 820 reaction system (Chemi-... 

Py-GC/MS can be applied for both qualitative and quantitative purposes. One typical use of quantitative analysis using pyrolysis is the determination of the amount of a specific polymer in a given complex matrix, such as a composite material, inorganic matrix, etc. Since solubilization is frequently a very difficult task for these materials, pyrolysis can provide quantitative information based on the level of the polymer marker generated by the thermal decomposition. Calibration is typically necessary in these situations, and similarly to other analytical procedures this can be achieved using a standard addition type procedure (see e.g. [17]) or a calibration with known amounts of polymer in a similar or identical matrix. Another case where the quantitation can be necessary is the determination of the amount of a comonomer in a copolymer sample. Successful quantitation by Py-GC/MS is reported in literature for various copolymers [25-39], etc. 

Other major shale constituents such as C, H, N, and S are determined by thermal decomposition and instrumental detection methods. Oxygen is determined by 14 MeV neutron activation analysis. Parr or Leco BTU bomb combustion and subsequent ion chromatographic determination is used for halogens, sulfate and nitrate. Ion chromatography is also suitable for anionic characterization of shale process waters. Two analytical procedures for oil shales should be used with caution. Kjeldahl nitrogen procedure has been found to give reproducible but considerably low results for certain oil... 

Fine DH, Rounbehler DP, Sawicki E, et al. 1977a. Determination of dimethylnitrosamine in air and water by thermal energy analysis validation of analytical procedures. Environ Sci Technol 11 577-580. 

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